Engine Controls - Tests W/codes - (G Series) Chevrolet Chevy Van G3500

INTRODUCTION

Most engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the computer system as a possible cause of problems, perform checks and inspections covered in the F - BASIC TESTING - 5.7L article. Failure to do so may result in lost diagnostic time.

If no faults found performing procedures in the BASIC TESTING - 5.7L article, proceed with DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no fault codes are present and driveability problems exist, proceed to the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in the TESTS W/O CODES article.

SELF-DIAGNOSTIC SYSTEM

Note. For On-Board Diagnostic System Check see the F - BASIC TESTING - 5.7L article.

Note. Powertrain Control Module (PCM) may also be referred to as Vehicle Control Module (VCM) in some diagnostic text and illustrations. Terms may be used interchangeably.

PCM/VCM is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, PCM/VCM will store a Diagnostic Trouble Code (DTC) and, in most cases, illuminate the Malfunction Indicator Light (MIL) located on instrument cluster. Malfunctions are recorded as hard failures or as intermittent failures.

There are 4 types of DTC category

1. Type "A" - Emissions related, turns on MIL the first time DTC sets.
2. Type "B" - Emissions related, turns on MIL if fault is active for 2 consecutive driving cycles.
3. Type "C" - Non-emissions related, does not turn on MIL, but will turn on SERVICE light.
4. Type "D" - Non-emissions related, does not turn on MIL or SERVICE light.

HARD FAILURES

Most hard failures cause MIL to illuminate and remain on until malfunction is repaired. If MIL comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined. See DIAGNOSTIC PROCEDURE .

If a sensor fails, PCM/VCM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but it will most likely display degraded driveability.

INTERMITTENT FAILURES

Intermittent failures cause MIL to flicker or glow and go out about 10 seconds after intermittent fault goes away. Corresponding DTC, however, will be retained in PCM/VCM memory. If related fault does not reoccur within 50 engine starts, trouble code will be erased from control module memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in the TESTS W/O CODES article.

Note. OBD II vehicles have options available in the scan tool DTC mode to display enhanced information available. However, to fully utilize information and procedures requires the use of a Tech 1 or 2 scan tool. See scan tool operator's manual for additional information.

The following are Tech 1 or 2 scan tool sub-menus in the DTC INFO and SPECIFIC DTC modes

DTC INFO MODE

Used to search for a specific type of stored DTC information. There are 7 choices in this mode. Technician may be instructed to test DTC(s) in a certain manner. Follow the affected DTC test procedures. To get complete description of any status, hit ENTER key before pressing the desired F-key.

DTC STATUS

This selection will display any DTC(s) that have not run during the current ignition cycle or have reported a test failure during this ignition up to a maximum of 33 DTCs. DTC test which run and passed will cause that affected DTC to be removed from scan tool screen.

FAIL THIS IGN.

This selection will display all DTCs that have failed during the present ignition cycle.

HISTORY

This selection will display only DTC(s) that are stored in the control module's history memory. It will not type "B" DTCs. It will display all type "A" and type "B" DTCs that have the MIL illuminated and have failed within the last 40 warm-up cycles. It will also display type "C" DTCs that have failed within the 40 warm-up cycles.

LAST TEST FAIL

This selection will display only DTCs that have failed the last time the test ran. The last test may have ran during the previous ignition cycle, if a type "A" or "B" DTC is displayed. For type "C" DTCs, the last failure must have occurred during the current ignition cycle to be displayed as LAST TEST FAIL.

MIL REQUEST

This selection will display only DTCs that are requesting the MIL. Type "C" DTCs cannot be displayed using this option. This selection will report type "B" DTCs only after the MIL has been requested.

NOT RUN SCC

Not Run Since Code Clear option will display up to 33 DTCs that have not run since DTCs were last cleared. Since any displayed DTCs have not run, their condition (passing or failing) is unknown.

TEST FAIL SCC

Test Fail Since Code Clear selection will display all active and history DTCs that have reported a test failure since the last time DTCs were cleared. DTCs that last failed over 40 warm-up cycles before this option is selected will not be displayed.

FAILED SINCE CLEAR

This message indicates the DTC has failed at least once within the last 40 warm-up cycles since the last time DTCs were cleared.

NOT RUN SINCE CL.

Not Run Since Cleared message indicates that the selected diagnostic test has not run since the last time DTCs were cleared. Therefore, the diagnostic test status (passed or failed) is unknown. After DTCs are cleared, this message will continue to be displayed until the diagnostic test runs.

NOT RUN THIS IGN.

Not Run This Ignition message indicates the selected diagnostic test has not run this ignition cycle.

TEST RAN AND PASSED

This message indicates the selected diagnostic test has

1. Passed the last test.
2. Ran and passed during this ignition cycle.
3. Ran and passed since DTCs were last cleared.
4. Test has not failed since DTCs were last cleared.

If this message is displayed, repair is done. If FAILED THIS IGN. message is displayed, repair is incomplete and further diagnosis is required.

DIAGNOSTIC PROCEDURE

Diagnosis of computerized engine control system should be performed in following order

1. Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK must be performed before using specific DTC testing procedure. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
2. If DTC(s) were displayed, determine whether codes are hard or intermittent trouble codes. Hard codes will cause MIL to illuminate continuously while engine is running. See «HARD OR INTERMITTENT TROUBLE CODE DETERMINATION»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__hard-or-intermittent-trouble-code-determination) . For diagnosing hard codes, proceed to appropriate DTC test. For diagnosing intermittent codes, proceed to INTERMITTENTS in the TESTS W/O CODES article.
3. If no DTCs are present and a driveability problem exists, refer to SYMPTOMS in the TESTS W/O CODES article. Doing so will help identify proper system or component to check in the SYSTEM/COMPONENT TESTS article.
4. After necessary repairs are made, clear DTCs, verify vehicle will enter "closed loop" operation and ensure DTC does not reset.

READING TROUBLE CODES

Note. Use of Tech 1 or 2 scan tool is required to retrieve DTCs. Refer to user reference manuals supplied with scan tool.

TROUBLE CODE DEFINITIONS

TROUBLE CODE DEFINITION

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, determine if DTC(s) are hard failure codes or intermittent failure codes. Diagnostic procedures will not always help analyze intermittent codes. To determine hard codes and intermittent codes

1. Enter diagnostic mode. Read and record all stored DTCs. Exit diagnostic mode, and clear DTCs. See «CLEARING DIAGNOSTIC TROUBLE CODES (DTC)»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__clearing-diagnostic-trouble-codes-dtc) .
2. Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. MIL should go out. Operate warm engine at specified RPM for 2 minutes and note MIL.
3. If MIL illuminates, enter diagnostic mode. Read and record DTCs. This will reveal hard failure codes. Oxygen sensor related codes may require a road test to reset hard failure after DTCs were cleared.
4. If MIL does not illuminate, all stored DTCs were intermittent failures, except as noted above. NOTE: DTCs will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer at normal operating temperature, vehicle speed and load. Therefore, some DTCs may not set in a service bay operational mode and may require road testing vehicle in order to duplicate conditions under which code will set.

CLEARING DIAGNOSTIC TROUBLE CODES (DTC)

To clear DTCs from memory, either to determine if malfunction will occur again or after making necessary repairs, disconnect power supply to ECM/PCM/VCM for at least 30 seconds or clear codes using a scan tool.

ECM/PCM/VCM LOCATION

On most models, ECM/PCM/VCM is located behind right or left side of dash, behind right or left kick panel, or on left or right side of engine compartment. For more precise location, see COMPONENT LOCATIONS in the SYSTEM/COMPONENT TESTS article.

Diagnostic Aids

Diagnostic aids are additional tips used to help diagnose trouble codes when inspected circuit is okay. Diagnostic aids may help lead to a definitive solution to trouble code problem.

SPECIAL TOOLS (DIAGNOSTIC)

Note. A scan tool plugged into DLC is used to read DTCs and check voltages in system on serial data line. A scan tool is REQUIRED to retrieve vehicle information.

Computerized engine control system is most easily diagnosed using scan tool; however, other tools may aid in diagnosing problems. These tools are a tachometer, test light, ohmmeter, digital voltmeter with a 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connectors at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic test. In addition, special jumper harnesses or testers may be required by manufacturer to facilitate diagnosis.

SCAN TOOL USAGE

Note. Before connecting scan tool to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received will be accurate. This is done by performing ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK located in the F - BASIC TESTING - 5.7L article. If vehicle does not pass OBD system check, information received may be invalid.

Scan tool is a specialized tester which, when plugged into DLC, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.

Scan tool cuts down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN DATA . They may also furnish information on output device (solenoids and motors) status. However, status parameters only indicate output signals have been sent to devices by PCM/VCM; they do not indicate whether devices have responded properly to signal. Verify proper response at output device using a voltmeter or test light.

A problem may exist even if DTCs are not present. About 80 percent of driveability problems occur without DTCs. Sensors that are out of calibration will not set a DTC but will cause driveability problems.

Using a scan tool is the easiest method of checking sensor specifications and other data parameters. Scan tool is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN DATA.

Note. If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, DO NOT use scan tool for diagnosis. Contact tester manufacturer for additional information.

SCAN DATA

Note. For scan data values, refer to scan tool manufacturer owner's manual or compare values with a known good component or vehicle.

SUMMARY

If no hard fault codes are present, driveability symptoms exist or intermittent DTC(s) exist, proceed to the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

CONNECTOR IDENTIFICATION

Note. For additional connector and terminal identification, see CONNECTOR IDENTIFICATION -- G VANS article

Scheme 13

Scheme 14

Scheme 15

Scheme 16

Scheme 17

Scheme 18

DIAGNOSTIC TROUBLE CODES

Note. Before clearing DTCs, perform On-Board Diagnostic (OBD) System Check. See the F - BASIC TESTING - 5.7L article. Record FREEZE FRAME and FAILURE RECORDS for reference during testing. Data will be erased when DTCs are cleared. If PCM/VCM is replaced, NEW PCM/VCM must be programmed using special manufacturer's equipment.

DTC P0101 - MAF SENSOR SYSTEM PERFORMANCE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Circuit Description

Mass Air Flow (MAF) sensor measure amount of air entering engine at a given time to determine fuel delivery. MAF sensor produces a frequency signal of about 2000 Hz at idle to 8000 Hz at maximum engine load. DTC will set if MAP signal does not match expected value based on barometric pressure, throttle position and engine speed parameters.

DTC will set when the following conditions are present

1. Engine is running.
2. No TP sensor DTCs are set.
3. No MAP sensor DTCs are set.
4. No EVAP DTCs are set.
5. EGR DTC P0401 is not set.
6. MAF DTCs P0102 or P0103 is not set.
7. System voltage is greater than 11 volts but less than 16 volts.
8. Canister purge duty cycle is less than 99.6 percent.
9. Change in throttle position is less than 3.9 percent.
10. EGR duty cycle is less than 89.9 percent.
11. EGR pintle position is less than 89.9 percent.
12. Engine vacuum is less than 90 kPa.
13. Throttle position is less than 89.8 percent.
14. Listed conditions are met for greater than 2 seconds.
15. Change in MAF sensor is greater than a calculated value.

Diagnostic Procedures

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC for DTC P0101. If scan tool indicates DTC P0101 FAILED THIS IGN, go to next step. If scan tool does not indicate DTC P0101 FAILED THIS IGN, see DIAGNOSTIC AIDS.
3. Check for the following conditions and repair as necessary: Objects blocking throttle body inlet screen. Intake manifold vacuum leaks. Vacuum leaks at throttle body. Vacuum leaks at EGR valve flange and pipes. Crankcase ventilation valve faulty, missing or incorrectly installed. If a problem was found, go to step 17). If a problem was not found, go to next step.
4. Turn ignition on, with throttle closed. Using scan tool, observe THROTTLE AT IDLE display. If scan tool displays YES, go to next step. If scan tool does not display YES, go to «DTC P0121»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0121-tp-sensor-system) test.
5. Turn ignition off. Disconnect MAF sensor connector. Turn ignition on, with engine off. Using DVOM, check voltage between ground and MAF sensor connector signal circuit. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 7).
6. Connect test light between MAF ignition feed circuit and ground circuit of MAF sensor connector. If test light illuminates, go to step 10). If test light does not illuminate, go to step 9).
7. If voltage is less than 4.5 volts, go to step 11). If voltage is not less than 4.5 volts, go to next step.
8. Turn ignition off. Disconnect VCM connector. Turn ignition on, with engine off. Check voltage between MAF signal circuit of VCM connector and ground. If voltage is zero volts, go to step 16). If voltage is not zero volts, go to step 14).
9. Connect test light between MAF ignition feed circuit of MAF sensor connector and ground. If test light illuminates, go to step 12). If test light does not illuminate, go to step 13).
10. Check for poor connection at MAF sensor and repair as necessary. If poor connection is present, go to step 17). If poor connection is not present, go to step 15).
11. Check for open, short to ground or short to MAF sensor ground circuit in MAF signal circuit between MAF sensor and VCM. Repair as necessary. After repairs, go to step 18). If circuit is okay, go to step 16).
12. Locate and repair open in ground circuit between MAF sensor and VCM. After repairs, go to step 18).
13. Locate and repair open in MAF ignition feed circuit to MAF sensor. After repairs, go to step 18).
14. Locate and repair short to voltage in MAF signal circuit between sensor and VCM. After repairs, go to step 18).
15. Replace MAF sensor. After replacing sensor, go to step 17).
16. Replace VCM. After replacing VCM, go to next step.
17. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select SPECIFIC DTC, then enter DTC P0101. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
18. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A faulty TP sensor or TP sensor circuit can cause VCM to incorrectly calculate predicted mass airflow value. Observe throttle angle with throttle closed. If throttle angle is not zero, check for throttle plate sticking or excessive deposits on throttle plate or throttle bore, TP signal circuit shorted to voltage, or for poor connection or high resistance in TP sensor ground circuit. If a problem is not found and TP sensor angle at closed throttle is not zero, replace TP sensor.

Inspect VCM connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection. Inspect MAF sensor harness routing to ensure it is not too close to high-voltage wires such as spark plug leads. Inspect wiring harness for damage. If harness is okay, observe scan tool while wiggling MAF sensor related connectors and wiring harness. A change in display will indicate location of fault.

A Wide Open Throttle (WOT) acceleration from a stop should cause mass airflow displayed on scan tool to increase from about 4-7 gm/s at idle to 100 gm/s or greater at 1-2 shift. If mass airflow does not indicate as specified, check for a plugged intake air duct or dirty air filter element. A skewed MAP sensor can cause BARO reading to be incorrectly calculated. To check MAP sensor, compare BARO reading on vehicle being diagnosed to a BARO reading on a normally operating vehicle. If a large difference is noted (over 8 kPa), replace MAP sensor. This may cause abnormally high IAC counts. If a comparison vehicle is not available, check IAC counts with engine running just off idle. If IAC counts are high, replace MAP sensor.

IF DTC P0101 can not be duplicated, FAIL RECORDS data can be useful in determining vehicle mileage since DTC was last set. This may determine how often DTC sets.

DTC P0102 - MAF SENSOR CIRCUIT LOW FREQUENCY

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Mass Airflow (MAF) sensor measure amount of air entering engine at a given time to determine fuel delivery. MAF sensor produces a frequency signal of 2000 Hz at idle to 8000 Hz at maximum engine load. DTC will set if MAF signal is less than possible range of a normally operating MAF sensor. DTC will test when the following conditions are present

Power up test

1. Engine not running.
2. Ignition is on for 2 seconds.

Low frequency test

1. Engine is running.
2. Engine run time is greater than 0.4 second.
3. System voltage is greater than 8 volts.
4. Throttle position is less than 89.8 percent.
5. Conditions present for greater than zero seconds.
6. MAF signal frequency is less than 100 Hz.

1. Perform Powertrain On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. With engine idling, monitor MAF display on scan tool. If MAF display is less than 2 gm/s, go to step 4). If MAF display is not less than 2 gm/s, go to next step.
3. Turn ignition on, with engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC for DTC P0102. If scan tool indicates DTC P0102 FAILED THIS IGN, go to next step. If scan tool does not indicate DTC P0102 FAILED THIS IGN, see DIAGNOSTIC AIDS.
4. Check for the following conditions and repair as necessary: Objects blocking MAF sensor inlet screen. Intake manifold vacuum leaks. Vacuum leaks at throttle body. Vacuum leaks at EGR valve flange and pipes. Crankcase ventilation valve faulty, missing or incorrectly installed. If a problem was found, go to step 14). If a problem was not found, go to next step.
5. Turn ignition off. Disconnect MAF sensor connector. Turn ignition on, with engine off. Using DVOM, check voltage between MAF signal circuit of MAF sensor connector and ground. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 9).
6. Connect test light between MAF ignition feed and ground circuits at MAF sensor connector. If test light illuminates, go to step 8). If test light does not illuminate, go to next step.
7. Connect test light between MAF ignition feed circuit at MAF sensor connector and battery ground. If test light illuminates, go to step 10). If test light does not illuminate, go to step 11).
8. Check for poor connection at MAF sensor. Repair as necessary. After repairs, go to step 14). If connection is okay, go to step 12).
9. Check for open, short to ground, short to MAF ground circuit or short to voltage in MAF signal circuit between MAF sensor and VCM. Repair as necessary. If MAF signal circuit is open or shorted, go to step 14). If MAF signal circuit is not open or shorted, go to step 13).
10. Locate and repair open in the ground circuit to MAF sensor. After repairs, go to step 14).
11. Locate and repair open in MAF ignition feed circuit to MAF sensor. After repairs, go to step 14).
12. Replace MAF sensor. After replacing sensor, go to step 14).
13. Replace VCM. Program replacement VCM using required equipment. After replacing and reprogramming VCM, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0102. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Inspect VCM connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connection. Inspect MAF sensor harness routing to ensure it is not too close to high-voltage wires such as spark plug leads. Inspect wiring harness for damage. If harness is okay, observe scan tool while wiggling MAF sensor related connectors and wiring harness. A change in display will indicate location of fault.

A Wide Open Throttle (WOT) acceleration from a stop should cause mass airflow displayed on scan tool to increase from about 4-7 gm/s at idle to 100 gm/s or greater at the time of the 1-2 shift. If mass airflow does not respond as specified, check for restrictions.

IF DTC P0102 cannot be duplicated, FAIL RECORDS data can be useful in determining vehicle mileage since DTC was last set. This may determine how often DTC sets.

DTC P0103 - MAF SENSOR CIRCUIT HIGH FREQUENCY

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Mass Airflow (MAF) sensor measures amount of air entering engine at a given time to determine fuel delivery. MAF sensor produces a frequency signal of 2000 Hz at idle to 8000 Hz at maximum engine load. DTC will set if MAF signal is greater than possible range of a normally-operating MAF sensor. DTC will set when the following conditions are present

1. Engine is not running.
2. Ignition is on for 2 seconds.

High frequency test

1. Engine is running.
2. Engine run time is at least 0.4 second.
3. System voltage is at least 8 volts.
4. Throttle position is less than 89.8 percent.
5. MAF sensor is at least 10.44 Hz.
6. Conditions are present for zero seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. With engine idling, monitor MAF display on scan tool. If MAF display is greater than 20 gm/s, go to step 4). If MAF is not greater than 20 gm/s, go to next step.
3. Turn ignition on, with engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC for DTC P0103. If scan tool indicates DTC P0103 FAILED THIS IGN?, go to next step. If scan tool does not indicate DTC P0103 FAILED THIS IGN?, see DIAGNOSTIC AIDS.
4. Turn ignition off. Disconnect MAF sensor connector. Start engine. With engine idling, monitor MAF frequency display on scan tool. If scan tool display is zero gm/s, go to next step. If scan tool display is not zero gm/s, go to step 7).
5. Check for poor connection at MAF sensor. Repair as necessary. After repairs, go to step 10). If connection is okay, go to next step.
6. Replace MAF sensor. After replacing sensor, go to step 10).
7. Check MAF sensor harness for incorrect routing near secondary ignition wires or coils, or other high voltage components such as solenoids, relays or motors. Repair/reroute wiring as necessary. After repairs, go to step 10). If routings are okay, go to next step.
8. Check for poor connection at MAF signal circuit terminal of VCM. Repair as necessary. After repairs, go to step 10). If connection is okay, go to next step.
9. Replace VCM. Program replacement VCM using required equipment. After replacing and reprogramming VCM, go to next step.
10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0103. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Inspect VCM connectors for backed-out terminals, improper mating, broken locks, improperly-formed or damaged terminals and poor terminal-to-wire connection. Inspect MAF sensor harness routing to ensure it is not too close to high-voltage wires such as spark plug leads. Inspect wiring harness for damage. If harness is okay, observe scan tool while wiggling MAF sensor related connectors and wiring harness. A change in display will indicate location of fault.

DTC P0106 - MAP SENSOR SYSTEM PERFORMANCE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). A 5-volt reference is applied to sensor. A variable resistor moves in relation to manifold pressure and a voltage signal is returned to VCM through MAP signal circuit. Voltage signal varies from 1-1.5 volts at closed throttle (high vacuum) to 4-4.5 volts at wide open throttle (low vacuum). A change in throttle position and engine speed should precede change in MAP. If change does not occur, MAP malfunction is present. VCM utilizes MAP signal and throttle position to determine fuel delivery.

1. Engine is running.
2. No TP sensor DTCs are set.
3. No IAC sensor DTCs are set.
4. No EGR DTCs are set.
5. Change in engine speed is less than 100 RPM.
6. Change in throttle position is less than 1.95 percent.
7. Change in EGR flow is less than 5 percent.
8. Change in IAC is less than 5 counts.
9. No change in brake switch status.
10. No change in clutch status (manual transmission).
11. No change in power steering switch status.
12. No change in A/C clutch status.
13. Conditions have stabilized for 2 seconds.
14. Conditions are met for 24 consecutive tests in a sample of 100 tests.
15. Change in MAP sensor is greater than .68 volt.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Monitor MAP sensor voltage on scan tool. If voltage is 0.4 volt, go to next step. If voltage is not 0.4 volt, go to step 6).
3. Disconnect and plug MAP sensor vacuum source. Connect a vacuum pump to MAP sensor. Start engine. Observe MAP sensor voltage on scan tool. Apply 10 in. Hg vacuum and observe MAP sensor voltage. Subtract this reading from voltage reading noted in step 2). If difference is greater than 1.5 volts, see DIAGNOSTIC AIDS. If difference is not greater than 1.5 volts, go to next step.
4. Check MAP sensor connections. If problem is found, go to next step. If connections are okay, go to step 7).
5. Repair connections as necessary. After repairs, go to step 7).
6. Replace MAP sensor. After replacing sensor, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0106. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check MAP sensor vacuum source for leaks, restrictions or faulty connections. Ensure vacuum source only supplies MAP sensor and not other systems such as cruise control, auxiliary vacuum gauges, etc.

DTC P0107 - MAP SENSOR CIRCUIT LOW VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). A 5-volt reference is applied to sensor. A variable resistor moves in relation to manifold pressure and a voltage signal is returned to VCM through MAP signal circuit. Voltage signal varies from 1.0-1.5 volts at closed throttle to 4.0-4.5 volts at wide open throttle (low vacuum). VCM utilizes MAP signal and throttle position to determine fuel delivery.

1. Engine running.
2. No TP sensor DTCs are set.
3. Throttle position is at least zero percent when engine speed is less than 800 RPM or throttle position is at least 12.5 percent when engine speed is greater than 800 RPM.
4. MAP sensor voltage is less than .25 volt.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is less than .5 volt, go to next step. If MAP sensor voltage is not less than .5 volt, go to step 5).
3. Turn ignition off. Disconnect MAP sensor connector. Connect a jumper wire between 5-volt reference circuit and signal circuit of MAP sensor connector. Turn ignition on. Monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4.7 volts, go to step 6). If MAP sensor voltage is not greater than 4.7 volts, go to next step.
4. Turn ignition off. Remove jumper wire. Using test light connected to battery voltage, probe MAP sensor connector signal circuit. Turn ignition on. Monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4.7 volts, go to step 9). If MAP sensor voltage is not greater than 4.7 volts, go to step 7).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for poor connection at MAP sensor. If a problem is found, go to step 12). If connection is okay, go to step 11).
7. Check for open in MAP sensor signal circuit. If a problem is found, go to step 12). If circuit is okay, go to next step.
8. Check for short to ground in MAP signal circuit. If a problem is found, go to step 12). If circuit is okay, go to step 13).
9. Check for open in MAP 5-volt reference circuit. If a problem is found, go to step 12). If circuit is okay, go to next step.
10. Check for short to ground in MAP 5-volt reference circuit. If a problem is found, go to step 12). If circuit is okay, go to step 13).
11. Replace MAP sensor. After replacing sensor, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Replace VCM. Program replacement VCM using required equipment. After replacing and reprogramming VCM, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0107. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent open in MAP signal circuit or 5-volt reference circuit will result in DTC P1107 setting. With ignition on and engine off, manifold pressure is equal to atmospheric pressure with signal voltage high. VCM uses information as an indication of vehicle altitude.

To test accuracy of a suspect sensor, compare reading with a known good vehicle. If DTC is intermittent, see the TESTS W/O CODES article. To check for intermittent connection, disconnect sensor from bracket and twist sensor by hand. Output changes greater than .1 volt indicate a poor connection or connector. If okay, replace sensor. Ensure electrical connection remains securely connected. If sensor is removed from intake manifold, sensor-to-manifold seal must be replaced.

DTC P0108 - MAP SENSOR CIRCUIT HIGH VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). A 5-volt reference is applied to sensor. A variable resistor moves in relation to manifold pressure and a voltage signal is returned to VCM through MAP signal circuit. Voltage signal varies from 1.0-1.5 volts at closed throttle to 4.0-4.5 volts at wide open throttle (low vacuum). VCM utilizes MAP signal and throttle position to determine fuel delivery.

1. No TP sensor DTCs are set.
2. Throttle position is less then .4 percent when engine speed is less than 1000 RPM or throttle position is less than 19.9 percent when engine speed is greater than 1000 RPM.
3. MAP sensor voltage is equal to or greater than 4.34 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. If engine idle is unstable, incorrect, or if manifold vacuum at idle is less than 15 in. Hg, repair as necessary. After repairs, install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is less than 4 volts, go to next step. If MAP sensor voltage is not less than 4 volts, go to step 4).
3. Turn ignition off. Disconnect MAP sensor connector. Turn ignition on. Monitor MAP sensor voltage using scan tool. If MAP sensor voltage is less than one volt, go to step 5). If MAP sensor voltage is not less than one volt, go to step 9).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Using a DVOM connected to ground, probe MAP sensor connector 5-volt reference circuit. If voltage is greater than 5.2 volts, go to step 10). If voltage is not greater than 5.2 volts, go to next step.
6. Using a test light connected to battery voltage, probe MAP sensor connector ground circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 14).
7. Check for restriction in MAP sensor vacuum source. If a problem was found, go to step 15). If a problem was not found, go to next step.
8. Replace MAP sensor. After replacing sensor, go to step 19).
9. Check for short to voltage in MAP signal circuit. If a problem was found, go to step 15). If circuit is okay, go to step 18).
10. Turn ignition off. Unplug VCM harness connector. Turn ignition on. Using DVOM connected to ground, check voltage on VCM harness 5-volt reference circuit. If voltage is greater than 5.2 volts, go to next step. If voltage is not greater than 5.2 volts, go to step 13).
11. Unplug EGR connector. Check voltage on EGR connector 5-volt reference circuit terminal. If voltage is greater than 5.2 volts, go to next step. If voltage is not greater than 5.2 volts, go to step 16).
12. Repair short to battery voltage in 5-volt reference circuit. After repairs, go to step 19).
13. With DVOM to ground, check voltage at VCM connector 5-volt reference circuit terminal. If voltage is greater than 5.2 volts, go to step 17). If voltage is not greater than 5.2 volts, go to step 18).
14. Repair MAP ground circuit. After repairs, go to step 19).
15. Repair as necessary. After repairs, go to step 19).
16. Replace EGR valve. After replacing EGR valve, go to step 19).
17. Repair short to voltage on the 5-volt reference circuit. After repairs, go to step 19).
18. Replace VCM. Program replacement VCM using required equipment. After replacing and reprogramming VCM, go to next step.
19. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0108. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
20. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent ground in MAP signal circuit or 5-volt reference circuit will result in DTC P1106 setting. With ignition on and engine off, manifold pressure is equal to atmospheric pressure with signal voltage high. VCM uses information as an indication of vehicle altitude.

To test accuracy of a suspect sensor, compare reading with that of a known-good vehicle. Reading should be 3.6-4.9 volts and 2 readings should be within .4 volt of each other. If DTC is intermittent, see the TESTS W/O CODES article. To check for intermittent connection, disconnect sensor from bracket and twist sensor by hand. Output changes greater than .1 volt indicate a poor connection or connector. If okay, replace sensor. Ensure electrical connection remains securely connected. If sensor is removed from intake manifold, replace sensor-to-manifold seal.

DTC P0112 - IAT SENSOR CIRCUIT VOLTAGE LOW

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Intake Air Temperature (IAT) sensor is a thermistor located in fresh air duct to throttle body. It is used to monitor temperature of air entering throttle body. VCM supplies and monitors 5 volts to sensor. When air is cool, sensor resistance will be high and VCM will sense a high voltage signal. When air is warm, sensor resistance will be low and VCM will sense a low voltage signal.

1. No VSS DTCs are set.
2. Vehicle speed is greater than 2 MPH.
3. Engine run time is greater than 100 seconds.
4. IAT voltage is less than .82 volt.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Monitor IAT sensor voltage on scan tool. If voltage is less than .82 volt, go to next step. If voltage is not less than .82 volt, go to step 5).
3. Turn engine off. Disconnect IAT sensor connector. Turn ignition on. Monitor IAT sensor voltage on scan tool. If voltage is greater than 4 volts, go to step 7). If voltage is not greater than 4 volts, go to next step.
4. Turn ignition off. Using DVOM, check resistance between IAT sensor connector terminals. If resistance is infinite, go to step 8). If resistance is not infinite, go to step 6).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Repair short to ground in IAT signal circuit. After repairs, go to step 9).
7. Replace IAT sensor. After replacing sensor, go to step 9).
8. Replace VCM. Program replacement VCM using required equipment. After replacing and reprogramming VCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0112. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool indicates temperature of ambient air entering throttle body. Air temperature should be very close to temperature of outside air and should gradually rise as engine warms and underhood temperature increases. If DTC P1112 is set, problem is intermittent. Check for short to ground in IAT signal circuit by wiggling wiring harness at various locations and monitoring IAT temperature or voltage on scan tool. Check for short to ground at point where scan tool display changed. Also, check for a skewed or mis-scaled sensor. See IAT TEMPERATURE-TO-RESISTANCE VALUES.

IAT TEMPERATURE-TO-RESISTANCE VALUES

DTC P0113 - IAT SENSOR CIRCUIT HIGH VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Intake Air Temperature (IAT) sensor is a thermistor located in fresh air duct to throttle body. It is used to monitor temperature of air entering throttle body. VCM supplies and monitors 5 volts to sensor. When air is cool, sensor resistance will be high and VCM will sense a high voltage signal. When air is warm, sensor resistance will be low and VCM will sense a low voltage signal.

1. No ECT sensor DTCs are set.
2. No VSS DTCs are set.
3. No MAF sensor DTCs are set.
4. Vehicle speed less than 2 MPH.
5. Engine coolant temperature is greater than 184.5°F (84.7°C).
6. Engine run time is greater than 100 seconds.
7. IAT voltage is greater than 4.9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Monitor IAT sensor voltage on scan tool. If voltage is greater than 4.9 volts, go to next step. If voltage is not greater than 4.9 volts, go to step 6).
3. Turn engine off. Disconnect IAT sensor connector. Turn ignition on. Connect a jumper wire between IAT sensor terminals. Monitor IAT sensor voltage on scan tool. If voltage is less than .82 volt, go to step 7). If voltage is not less than .82 volt, go to next step.
4. Connect a jumper wire between IAT signal circuit of IAT sensor connector and ground. Monitor IAT sensor voltage on scan tool. If voltage is less than .82 volt, go to step 8). If voltage is not less than .82 volt, go to next step.
5. Check if «DTC P0123»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0123-tp-sensor-circuit) is also set. If DTC P0123 is set, go to DTC P0123. If DTC P0123 is not set, go to step 9).
6. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
7. Check for poor connections at IAT sensor and VCM. If a problem was found, go to step 10). If a problem is not found, go to step 11).
8. Check for open in IAT ground circuit between IAT sensor and VCM. If IAT ground circuit is open, go to step 10). If IAT ground circuit is not open, go to step 12).
9. Check for open in IAT signal circuit between IAT sensor and VCM. If IAT signal circuit is open, go to step 10). If IAT signal circuit is not open, go to step 12).
10. Repair as necessary. After repairs, go to step 13).
11. Replace IAT sensor. After replacing sensor, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing and reprogramming VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0113. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool indicates temperature of ambient air entering throttle body. Air temperature should be very close to temperature of outside air and should gradually rise as engine warms and underhood temperature increases. If DTC P1111 is set, problem is intermittent. Check for poor connections at IAT sensor and VCM by wiggling wiring harness at various locations and monitoring IAT temperature or voltage on scan tool. Check for poor connection at point where scan tool display changed. Also, check for a skewed or mis-scaled sensor. See the IAT TEMPERATURE-TO-RESISTANCE VALUES table.

DTC P0117 - ECT SENSOR CIRCUIT LOW VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Engine Coolant Temperature (ECT) sensor is a thermistor located in intake manifold cooling system passage used to monitor engine coolant temperature. VCM supplies 5 volts to sensor. When engine coolant is cool, sensor resistance will be high and VCM will sense a high voltage signal. When engine coolant is warm, sensor resistance will be low and VCM will sense a low voltage signal.

1. Engine is running.
2. ECT voltage is less than .78 volt for 5 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Monitor ECT sensor voltage on scan tool. If voltage is less than .82 volt, go to next step. If voltage is not less than .82 volt, go to step 5).
3. Turn engine off. Disconnect ECT sensor connector. Turn ignition on. Monitor ECT sensor voltage on scan tool. If voltage is greater than 4 volts, go to step 7). If voltage is not greater than 4 volts, go to next step.
4. Turn ignition off. Using DVOM, check resistance between ECT sensor connector terminals. If resistance is infinite, go to step 8). If resistance is not infinite, go to step 6).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Repair short to ground in ECT signal circuit. After repairs, go to step 9).
7. Replace ECT sensor. After replacing sensor, go to step 9).
8. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0117. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool displays engine temperature in degrees centigrade. After engine is started, temperature should steadily rise to about 90C then stabilize when thermostat opens. A poor connection or open in 5-volt reference circuit or ground circuit will cause DTC P0117 to set. A skewed or mis-scaled sensor could cause poor driveability conditions. See ECT TEMPERATURE-TO-RESISTANCE VALUES .

ECT TEMPERATURE-TO-RESISTANCE VALUES

DTC P0118 - ECT SENSOR CIRCUIT HIGH VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Engine Coolant Temperature (ECT) sensor is a thermistor located in intake manifold cooling system passage used to monitor engine coolant temperature. VCM applies and monitors 5 volts to sensor. When engine coolant is cool, sensor resistance will be high and VCM will sense a high voltage signal. When engine coolant is warm, sensor resistance will be low and VCM will sense a low voltage signal.

1. Engine is running.
2. ECT voltage is greater than 4.9 volts for 5 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Monitor ECT sensor voltage on scan tool. If voltage is greater than 4.9 volts, go to next step. If voltage is not greater than 4.9 volts, go to step 5).
3. Turn engine off. Disconnect ECT sensor connector. Turn ignition on. Connect a jumper wire between ECT sensor terminals. Monitor ECT sensor voltage on scan tool. If voltage is less than .82 volt, go to step 6). If voltage is not less than .82 volt, go to next step.
4. Connect a jumper wire between ECT signal circuit of ECT sensor connector and ground. Monitor ECT sensor voltage on scan tool. If voltage is less than .82 volt, go to step 7). If voltage is not less than .82 volt, go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for poor connections at ECT sensor and VCM. If a problem was found, go to step 10). If a problem is not found, go to step 11).
7. Check for open in ECT ground circuit between ECT sensor and VCM. If ECT ground circuit is open, go to step 10). If ECT ground circuit is not open, go to step 12).
8. Check if «DTC P0123»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0123-tp-sensor-circuit) is also set. If DTC P0123 is set, go to DTC P0123. If DTC P0123 is not set, go to next step.
9. Check for open in ECT signal circuit between ECT sensor and VCM. If ECT signal circuit is open, go to next step. If ECT signal circuit is not open, go to step 12).
10. Repair as necessary. After repairs, go to step 13).
11. Replace ECT sensor. After replacing sensor, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0118. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test.

Check harness routing for short to ground in 5-volt reference circuit. Scan tool displays engine temperature in degrees centigrade. After engine is started, temperature should steadily rise to about 90C then stabilize when thermostat opens. A skewed or mis-scaled sensor could cause poor driveability conditions. See ECT TEMPERATURE-TO-RESISTANCE VALUES .

DTC P0121 - TP SENSOR SYSTEM PERFORMANCE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle opening. Signal voltage varies from about .5 volt at idle to about 4.5 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by VCM for fuel control and most VCM control outputs.

1. Engine is running.
2. No MAP sensor DTCs are set.
3. No TP sensor DTCs are set.
4. No IAC sensor DTCs are set.
5. MAP is less than 50 kPa.
6. Change in throttle position is less than 2 percent.
7. Last throttle position is greater than calculated throttle position based on engine RPM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, observe TP sensor value. If TP sensor value is greater than 2 percent, go to step 4). If TP sensor value is not greater than 2 percent, go to next step.
3. Depress throttle while observing scan tool. Throttle value should increase from about zero percent to 99.6 percent. Release throttle. Throttle value should drop to about 2 percent. If TP sensor value is greater than 2 percent, go to next step. If TP sensor value is not greater than 2 percent, go to step 5).
4. Disconnect TP sensor connector. Using scan tool, monitor TP sensor. If TP sensor voltage is about zero volts, go to step 6). If TP sensor voltage is not about zero volts, go to step 9).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for poor connection at TP sensor. If a problem was found, go to next step. If a problem was not found, go to step 8).
7. Repair as necessary. After repairs, go to step 10).
8. Replace TP sensor. After replacing sensor, go to step 10).
9. Replace VCM. After replacing VCM, go to next step.
10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0121. Operate vehicle within the conditions for setting this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, repeat step 2).
11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test.

Scan tool displays throttle position in volts. Voltage should be about .45-.85 volt with throttle closed and ignition on. Voltage should steadily increase as throttle is moved toward wide open throttle. Scan tool throttle angle percentage will display as zero percent with closed throttle and 100 percent with wide open throttle. Check connector and sensor terminals for moisture or corrosion. Clean and replace as necessary. If corrosion is found, check connector seal and repair or replace as necessary. If DTC is intermittent, see the TESTS W/O CODES article.

DTC P0122 - TP SENSOR CIRCUIT LOW VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle opening. Signal voltage varies from about 0.5 volt at idle to about 4.5 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by VCM for fuel control and most VCM control outputs.

1. Engine is running.
2. TP sensor voltage is less than .25 volt.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. With throttle closed, monitor TP signal voltage using scan tool. If TP signal voltage is less than .15 volt, go to next step. If TP signal voltage is not less than .15 volt, go to step 5).
3. Disconnect TP sensor connector. Connect a jumper wire between TP signal circuit and 5-volt reference circuit of TP sensor connector. Monitor TP signal voltage using scan tool. If TP signal voltage is greater than 4 volts, go to step 12). If TP signal voltage is not greater than 4 volts, go to next step.
4. Using a test light connected to battery voltage, probe TP sensor connector signal circuit. Monitor TP signal voltage using scan tool. If TP signal voltage is greater than 4 volts, go to step 6). If TP signal voltage is not greater than 4 volts, go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in 5-volt reference circuit. If a problem is found, go to step 11). If a problem is not found, go to next step.
7. Check for short to ground in 5-volt reference circuit. If a problem is found, go to step 11). If a problem is not found, go to step 10).
8. Check for open in TP signal circuit. If a problem is found, go to step 11). If a problem is not found, go to next step.
9. Check for short to ground in TP signal circuit. If a problem is found, go to step 11). If a problem is not found, go to next step.
10. Check for poor connections at VCM. If a connection problem is found, go to step 11). If a problem is not found, go to step 13).
11. Repair circuit as necessary. After repairs, go to step 14).
12. Replace TP sensor. After replacing sensor, go to step 14).
13. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0122. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool displays throttle position in volts. Voltage should be .45-.85 volt with throttle closed and ignition on. An open or short to ground in 5-volt reference circuit or TP signal circuit will cause DTC P0122 to set. If DTC is intermittent, see the TESTS W/O CODES article. While depressing accelerator pedal with engine stopped and ignition on, TP signal voltage should vary from less than 1.25 volts with throttle closed to greater than 4.5 volts with WOT.

DTC P0123 - TP SENSOR CIRCUIT HIGH VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Throttle Position (TP) sensor signal circuit provides a voltage signal that changes relative to throttle opening. Signal voltage varies from about 0.5 volt at idle to about 4.0 volts at Wide Open Throttle (WOT). Input is used by VCM for fuel control and most VCM control outputs.

1. Engine is running.
2. TP sensor voltage is greater than 4.7 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. With throttle closed, monitor TP signal voltage using scan tool. If TP signal voltage is greater than 4.8 volts, go to next step. If TP signal voltage is not greater than 4.8 volts, go to step 4).
3. Disconnect TP sensor connector. Monitor TP signal voltage using scan tool. If TP signal voltage is less than 0.2 volt, go to next step. If TP signal voltage is not less than 0.2 volt, go to step 8).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. With DVOM to ground, check voltage on 5-volt reference circuit at TP sensor connector. If voltage is greater than 5.2 volts, go to step 9). If not greater than 5.2 volts, go to next step.
6. Using test light connected to battery voltage, probe TP sensor connector ground circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 13).
7. Replace TP sensor. After replacing sensor, go to step 18).
8. Check for short to voltage in TP sensor signal circuit. If a problem is found, go to step 14). If a problem is not found, go to step 17).
9. Turn ignition off. Unplug VCM Gray connector. Turn ignition on. With DVOM connected to ground, check TP sensor 5-volt reference circuit at VCM connector. If voltage is greater than 5.2 volts, go to step 12). If not, go to next step.
10. With DVOM to ground, check voltage at VCM connector EGR 5-volt reference circuit terminal. If voltage is greater than 5.2 volts, go to next step. If not, go to step 17).
11. Unplug EGR valve connector. Again measure voltage on VCM connector EGR 5-volt reference circuit terminal. If voltage is greater than 5.2 volts, go to step 16). If not, go to step 15).
12. Repair short to voltage on 5-volt reference circuit. After repairs, go to step 18).
13. Check for open in TP ground circuit. If problem exists, repair as necessary and go to next step. If no problem exists, go to step 17).
14. Repair circuit as necessary. After repairs, go to step 18).
15. Replace EGR valve. After replacing EGR valve, go to step 18).
16. Repair short to voltage on 5-volt reference circuit. After repairs, go to step 18).
17. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
18. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0123. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
19. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool displays throttle position in volts. Voltage should be .45-.85 volt with throttle closed and ignition on or at idle. Voltage should steadily increase as throttle is moved toward WOT. Scan tool throttle angle percentage will display as zero percent being closed throttle and 100 percent being WOT. While depressing accelerator pedal with engine stopped and ignition on, TP signal voltage should vary from less than 1.25 volts with throttle closed to greater than 4.5 volts with WOT. An open in TP ground circuit or short to voltage in TP signal circuit will cause DTC P0123 to set. If DTC is intermittent, see the TESTS W/O CODES article.

DTC P0125 - ECT EXCESSIVE TIME TO CLOSED LOOP

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

While engine is warming, VCM monitors ECT sensor to determine the amount of time it takes engine to reach coolant temperature required for closed loop operation. Test will not be run if either intake air or engine coolant temperature are less than predetermined temperature. VCM will only run test on a cold start and only once per cold start.

1. Engine running.
2. ECT is greater than 15°F (-9°C).
3. IAT is greater than 19°F (-7°C).
4. Vehicle speed is greater than one MPH.
5. Start-up ECT is less than 104°F (40°C).
6. Closed-loop timer greater than 4 minutes.
7. Minimum stabilized ECT is less than 68°F (20°C).

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Allow engine to completely cool. Install scan tool. Turn ignition on. Using scan tool, monitor intake air temperature and engine coolant temperature values. Compare values. If values are the same, go to next step. If values are not the same, go to «DTC P0117»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0117-ect-sensor-circuit) .
3. Start and run engine. Monitor engine coolant temperature using scan tool. If engine coolant temperature steadily rises to greater than 95°F (35°C) within 9 minutes, see DIAGNOSTIC AIDS. If engine coolant temperature does not steadily rise to greater than 95°F (35°C) within 9 minutes, go to next step.
4. Check cooling system coolant level. If a problem was found, repair cooling system. If a problem was not found, go to next step.
5. Compare engine coolant temperature displayed on scan tool to actual coolant temperature. If values are about the same, repair cooling system. If values are not about the same, go to next step.
6. Replace ECT sensor. After replacing sensor, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0125. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

When DTC P0125 is set, ECT sensor is skewed or engine thermostat does not operate properly. An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect VCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If connections and harness are okay, observe scan tool connected between VCM connector terminals while wiggling related connectors and wiring harness. A change in display will indicate location of fault.

DTC P0131 - HO2S CIRCUIT LOW VOLTAGE BANK 1, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (360°C). DTC P0131, DTC P0132, an open sensor circuit or a cold sensor causes open loop operation. DTC P0131 determines if HO2S or circuit is shorted low by checking for a lean condition during steady throttle and power enrichment.

DTC will test when the following conditions are present

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S voltage using scan tool. If HO2S voltage is less than .086 volt, go to next step. If HO2S voltage is not less than .086 volt, go to step 4).
3. Turn ignition off. Disconnect HO2S connector. Connect a jumper wire between HO2S ground circuit of HO2S connector (VCM side) and ground. Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is .35-.55 volt, go to step 7). If HO2S voltage is not .35-.55 volt, go to step 5).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Check for short to ground in HO2S signal circuit. If a problem is found, go to next step. If a problem is not found, go to step 8).
6. Repair circuit as necessary. After repairs, go to step 9).
7. See DIAGNOSTIC AIDS.
8. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0131. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Using scan tool, observe Long Term (LT) fuel trim values at different RPM and air flow conditions. Scan tool should display fuel trim cells so that LT fuel trim values can be check in each cell to determine when DTC may have set. If DTC is set, LT fuel trim values will be about 158 or greater.

Check for mispositioned HO2S wire pigtail contacting exhaust manifold. Check for intermittent ground in wire between connector and sensor. Check for poor VCM to engine block ground. Check for lean fuel injectors. Check for water near in-tank fuel pump inlet that may be delivered to injectors. Water causes a lean exhaust and can cause DTC to set.

System will be lean if fuel pressure is too low. Monitor fuel pressure while driving vehicle at various speeds and loads to verify pressure. Check for an exhaust leak that can cause outside air to be pulled into exhaust and past sensor. Check for vacuum or crankcase leaks that can cause a lean condition and possibly high idle. If all above checks are okay, HO2S is faulty. DO NOT solder HO2S wires.

DTC P0132 - HO2S CIRCUIT HIGH VOLTAGE BANK 1, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0131, DTC P0132, an open sensor circuit or a cold sensor causes open loop operation. DTC P0132 determines if HO2S or circuit is shorted high by checking for a rich condition during steady throttle.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Warm engine to normal operating temperature. Place vehicle in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S voltage using scan tool. If HO2S voltage is fixed at greater than .976 volt, go to next step. If HO2S voltage is not as specified, go to step 4).
3. Turn ignition off. Disconnect HO2S harness connector. Connect jumper wires between ground, and HO2S ground and HO2S signal circuits of HO2S harness connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is less than 0.2 volt, go to step 5). If HO2S voltage is not less than 0.2 volt, go to step 6).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. See DIAGNOSTIC AIDS.
6. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0132. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

System will be rich if fuel pressure is too high. VCM can compensate for some increase in fuel pressure, but if pressure is too high, DTC may set. Check for rich or leaking injector. Check for fuel contaminated oil. Check for fuel saturation in EVAP canister purge. If full of fuel, check canister control and hoses. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

Check for an intermittent TP sensor output that will cause system to go rich due to false indication of throttle moving. Check for false rich indication due to silicon contamination of HO2S indicated by DTC accompanied by lean driveability conditions and a powdery white deposit on sensor.

Check for internally shorted HO2S as indicated by a voltage of greater than one volt on scan tool. Disconnect HO2S. If voltage changes from greater than one volt to about .45 volt, replace HO2S. DO NOT solder HO2S wires.

DTC P0133 - HO2S SLOW RESPONSE BANK 1, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. VCM monitors activity for 100 seconds after closed loop. During monitored period, VCM counts how often HO2S switches between rich and lean. VCM determines average switching time. If average switching time is too slow, DTC P0133 will set.

HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S is operating properly by checking response time.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.
10. HO2S transition time from lean to rich is greater than 85 milliseconds.
11. HO2S transition time from rich to lean is greater than 85 milliseconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other HO2S DTCs are set. If any other HO2S DTCs are set, go to applicable DTC test. If no other HO2S DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is not greater than 4 volts, go to next step.
4. Visually inspect exhaust system near HO2S for leaks. If a problem was found, go to step 8). If a problem was not found, go to next step.
5. Visually inspect if HO2S was properly installed. If a problem was found, go to step 8). If a problem was not found, go to next step.
6. Check if HO2S connection is contacting engine or exhaust system. If a problem was found, go to step 8). If a problem was not found, go to next step.
7. Remove HO2S and inspect for silicon contamination (a white powdery deposit on portion of sensor exposed to exhaust stream). Also, inspect for engine oil/coolant or lead contamination. If contamination is found, go to step 9). If contamination is not found, see DIAGNOSTIC AIDS.
8. Repair as necessary. After repairs, go to step 11).
9. Repair source of contamination. After repairs, go to next step.
10. Replace HO2S. After replacing sensor, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0133. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check HO2S heater operation. DO NOT solder HO2S wires.

DTC P0134 - HO2S CIRCUIT INSUFFICIENT ACTIVITY BANK 1, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S or HO2S circuit is open.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.
10. Engine run time is greater than 2 minutes.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Connect scan tool. Warm engine to normal operating temperature. Run engine at greater than 1200 RPM for 2 minutes. If scan tool indicates closed loop, go to step 5). If scan tool does not indicate closed loop, go to next step.
3. Turn ignition off. Disconnect HO2S harness connector. Connect jumper wires between ground, and HO2S ground and HO2S signal circuits of HO2S connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is less than .2 volt, go to step 7). If HO2S voltage is not less than .2 volt, go to next step.
4. Remove jumper wires and reconnect HO2S connector. Turn ignition off. Disconnect Blue VCM connector. Using test light, probe VCM connector HO2S signal circuit to battery voltage. If test light illuminates, go to step 6). If test light does not illuminate, go to step 9).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in HO2S signal circuit. If circuit is open, go to step 11). If circuit is okay, go to step 8).
7. Check for poor connection at HO2S. If connection is faulty, go to step 11). If connection is okay, go to step 10).
8. Check for poor connection at VCM connector. If a problem is found, go to step 11). If a problem is not found, go to step 12).
9. Repair open in HO2S ground circuit. After repairs, go to step 13).
10. Replace HO2S. After replacing sensor, so to step 13).
11. Repair circuit as necessary. After repairs, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0134. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

With ignition on and engine off, HO2S voltage on scan tool should gradually decrease to less than .15 volt indicating heater is operating properly. If voltage does not decrease as specified, disconnect HO2S connector and connect a test light between HO2S connector terminals "C" and "D" (engine harness side). If test light illuminates, replace HO2S. If test light does not illuminate, repair open in HO2S heater ground circuit or HO2S ignition feed circuit.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage of greater than .6 volt and less than .3 volt, to a fixed voltage of about .45 volt. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

DTC P0135 - HO2S HEATER CIRCUIT BANK 1, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S heater is operating properly by monitoring amount of time necessary for HO2S to become active after start-up.

1. System voltage is greater than 9 volts but less than 17 volts.
2. MAF is less than 27 gm/s.
3. Engine run time is greater than 2 seconds.
4. Engine coolant temperature is less than 90°F (32°C).
5. Intake air temperature is less than 90°F (32°C).
6. Difference between engine coolant temperature and intake air temperature is less than 41°F (5°C).
7. Elapsed time to obtain .3-.6 volt is greater than calculated value.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage gradually decreases by .15 volt, go to step 5). If HO2S voltage does not gradually decrease by .15 volt, go to next step.
3. Turn ignition off. Disconnect HO2S connector. Using test light, probe HO2S connector terminal "D" (engine harness side) to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 6).
4. Connect test light between terminals "C" and "D" of HO2S connector (engine harness side). If test light illuminates, go to step 7). If test light does not illuminate, go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in 20-amp ENG-1 fuse. If fuse is open, go to step 14). If fuse is not open, go to step 9).
7. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 15).
8. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 10).
9. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 11).
10. Repair open in HO2S heater ground circuit. After repairs, go to step 16).
11. Check for open in HO2S ignition feed circuit. If circuit is open, go to step 13).
12. Repair poor connection. After repairs, go to step 16).
13. Repair open in HO2S ignition feed circuit. After repairs, go to step 16).
14. Repair short to ground in HO2S ignition feed circuit and replace fuse. After repairs, go to step 16).
15. Replace HO2S. After replacing sensor, go to next step.
16. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0135. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. DO NOT solder HO2S wires.

DTC P0137 - HO2S CIRCUIT LOW VOLTAGE BANK 1, SENSOR 2

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0137, DTC P0138, an open sensor circuit or a cold sensor causes open loop operation. DTC P0137 determines if HO2S or circuit is shorted low by checking for a lean condition during steady throttle and power enrichment.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S voltage using scan tool. If HO2S voltage is fixed at less than .086 volt, go to next step. If HO2S voltage is not as specified, go to step 4).
3. Turn ignition off. Disconnect HO2S connector. Connect a jumper wire between ground and HO2S low circuit of HO2S connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is .35-.55 volt, go to step 7). If HO2S voltage is not .35-.55 volt, go to step 5).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Check for short to ground in HO2S signal circuit. If a problem is found, go to next step. If a problem is not found, go to step 8).
6. Repair circuit as necessary. After repairs, go to step 9).
7. See DIAGNOSTIC AIDS.
8. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0137. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Using scan tool, observe Long Term (LT) fuel trim values at different RPM and air flow conditions. Scan tool should display fuel trim cells so that LT fuel trim values can be check in each cell to determine when DTC may have set. If DTC is set, LT fuel trim values will be about 158 or greater.

Check for mispositioned HO2S wire pigtail contacting exhaust manifold. Check for intermittent ground in wire between connector and sensor. Check for poor VCM to engine block ground. Check for lean fuel injectors. Check for water near in-tank fuel pump inlet that may be delivered to injectors. Water causes a lean exhaust and can cause DTC to set.

System will be lean if fuel pressure is too low. Monitor fuel pressure while driving vehicle at various speeds and loads to verify pressure. Check for an exhaust leak that can cause outside air to be pulled into exhaust and past sensor. Check for vacuum or crankcase leaks that can cause a lean condition and possibly high idle. If all above checks are okay, HO2S is faulty. DO NOT solder HO2S wires.

DTC P0138 - HO2S CIRCUIT HIGH VOLTAGE BANK 1, SENSOR 2

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0137, DTC P0138, an open sensor circuit or a cold sensor causes open loop operation. DTC P0138 determines if HO2S or circuit is shorted high by checking for a rich condition during steady throttle.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S voltage using scan tool. If HO2S voltage is fixed at greater than .976 volt, go to next step. If HO2S voltage is not as specified, go to step 4).
3. Turn ignition off. Disconnect HO2S connector. Connect jumper wires between ground, and HO2S ground and HO2S signal circuits of HO2S connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If scan HO2S voltage is less than .2 volt, go to step 5). If HO2S voltage is not less than .2 volt, go to step 6).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. See DIAGNOSTIC AIDS.
6. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0138. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

System will be rich if fuel pressure is too high. VCM can compensate for some increase in fuel pressure, but if pressure is too high, DTC may set. Check for rich or leaking injector. Check for fuel contaminated oil. Check for fuel saturation in EVAP canister purge. If full of fuel, check canister control and hoses. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

Check for an intermittent TP sensor output that will cause system to go rich due to false indication of throttle moving. Check for false rich indication due to silicone contamination of HO2S indicated by DTC accompanied by lean driveability conditions and a powdery white deposit on sensor.

Check for internally shorted HO2S as indicated by a voltage of greater than one volt on scan tool. Disconnect HO2S. If voltage changes from greater than one volt to about .45 volt, replace HO2S. DO NOT solder HO2S wires.

DTC P0140 - HO2S INSUFFICIENT ACTIVITY BANK 1, SENSOR 2

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuit. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up, allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S or HO2S circuit is open.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.
10. Engine run time is greater than 2 minutes.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Connect scan tool. Warm engine to normal operating temperature. Run engine at greater than 1200 RPM for 2 minutes. If scan tool indicates closed loop, go to step 5). If scan tool does not indicate closed loop, go to next step.
3. Turn ignition off. Disconnect HO2S harness connector. Connect jumper wires between ground, and HO2S ground and HO2S signal circuits of HO2S connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is less than .2 volt, go to step 7). If HO2S voltage is not less than .2 volt, go to next step.
4. Remove jumper wires and reconnect HO2S connector. Turn ignition off. Disconnect Blue VCM connector. Using test light, probe VCM connector HO2S signal circuit to battery voltage. If test light illuminates, go to step 6). If test light does not illuminate, go to step 9).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in HO2S signal circuit. If circuit is open, go to step 11). If circuit is okay, go to step 8).
7. Check for poor connection at HO2S connector. If connection is faulty, go to step 11). If connection is okay, go to step 10).
8. Check for poor connection at VCM connector. If connection is okay, go to step 11). If connection is okay, go to step 12).
9. Repair open in HO2S ground circuit. After repairs, go to step 13).
10. Replace HO2S. After replacing sensor, go to step 13).
11. Repair circuit as necessary. After repairs, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0140. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

With ignition on and engine off, HO2S voltage on scan tool should gradually decrease to less than .15 volt indicating heater is operating properly. If voltage does not decrease as specified, disconnect HO2S connector and connect a test light between HO2S connector terminals "C" and "D" (engine harness side). If test light illuminates, replace HO2S. If test light does not illuminate, repair open in HO2S heater ground circuit or HO2S ignition feed circuit.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage of greater than .6 volt and less than .3 volt, to a fixed voltage of about .45 volt. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

DTC P0141 - HO2S HEATER CIRCUIT BANK 1, SENSOR 2

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S heater is operating properly by monitoring amount of time necessary for HO2S to become active after start-up.

1. System voltage is greater than 9 volts but less than 17 volts.
2. MAF is less than 27 gm/s.
3. Engine run time is greater than 2 seconds.
4. Engine coolant temperature is less than 90°F (32°C).
5. Intake air temperature is less than 90°F (32°C).
6. Difference between engine coolant temperature and intake air temperature is less than 41°F (5°C).
7. Elapsed time to obtain .3-.6 volt is greater than calculated value.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage gradually decreases by .15 volt, go to step 5). If HO2S voltage does not gradually decrease by .15 volt, go to next step.
3. Turn ignition off. Disconnect HO2S connector. Using test light, probe HO2S connector terminal "D" (engine harness side) to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 6).
4. Connect test light between terminals "C" and "D" of HO2S connector (engine harness side). If test light illuminates, go to step 7). If test light does not illuminate, go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in 20-amp ENG-1 fuse. If fuse is open, go to step 14). If fuse is not open, go to step 9).
7. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 15).
8. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 10).
9. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 11).
10. Repair open in HO2S heater ground circuit. After repairs, go to step 16).
11. Check for open in HO2S ignition feed circuit. If circuit is open, go to step 13).
12. Repair poor connection. After repairs, go to step 16).
13. Repair open in HO2S ignition feed circuit. After repairs, go to step 16).
14. Repair short to ground in HO2S ignition feed circuit and replace fuse. After repairs, go to step 16).
15. Replace HO2S. After replacing sensor, go to next step.
16. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0141. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. DO NOT solder HO2S wires.

DTC P0143 - HO2S CIRCUIT LOW VOLTAGE BANK 1, SENSOR 3

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316C). DTC P0143, DTC P0144, an open sensor circuit or a cold sensor causes open loop operation. DTC P0143 determines if HO2S or circuit is shorted low by checking for a lean condition during steady throttle and power enrichment.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S voltage using scan tool. If HO2S voltage is fixed at less than .026 volt, go to next step. If HO2S voltage is not fixed at less than .026 volt, go to step 4).
3. Turn ignition off. Disconnect HO2S connector. Connect a jumper wire between HO2S ground circuit of HO2S connector (VCM side) and ground. Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is .35-.55 volt, see DIAGNOSTICS AIDS. If HO2S voltage is not .35-.55 volt, go to step 5).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Check for short to ground in HO2S signal circuit. If a problem is found, go to next step. If a problem is not found, go to step 7).
6. Repair circuit as necessary. After repairs, go to step 8).
7. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
8. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0143. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
9. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Using scan tool, observe Long Term (LT) fuel trim values at different RPM and air flow conditions. Scan tool should display fuel trim cells so that LT fuel trim values can be check in each cell to determine when DTC may have set. If DTC is set, LT fuel trim values will be about 158 or greater.

Check for mispositioned HO2S wire pigtail contacting exhaust manifold. Check for intermittent ground in wire between connector and sensor. Check for poor VCM to engine block ground. Check for lean fuel injectors. Check for water near in-tank fuel pump inlet that may be delivered to injectors. Water causes a lean exhaust and can cause DTC to set.

System will be lean if fuel pressure is too low. Monitor fuel pressure while driving vehicle at various speeds and loads to verify pressure. Check for an exhaust leak that can cause outside air to be pulled into exhaust and past sensor. Check for vacuum or crankcase leaks that can cause a lean condition and possibly high idle. If all above checks are okay, HO2S is faulty. DO NOT solder HO2S wires.

DTC P0144 - HO2S CIRCUIT HIGH VOLTAGE BANK 1, SENSOR 3

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316C). DTC P0143, DTC P0144, an open sensor circuit or a cold sensor causes open loop operation. DTC P0144 determines if HO2S or circuit is shorted high by checking for a rich condition during steady throttle.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S voltage using scan tool. If HO2S voltage is fixed at greater than .976 volt, go to next step. If HO2S voltage not fixed at greater than .976 volt, go to step 4).
3. Turn ignition off. Disconnect HO2S harness connector. Connect jumper wires between ground, and HO2S ground and HO2S signal circuits of HO2S connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is less than .2 volt, see DIAGNOSTIC AIDS. If not, go to step 5).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0144. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

System will be rich if fuel pressure is too high. VCM can compensate for some increase in fuel pressure, but if pressure is too high, DTC may set. Check for rich or leaking injector. Check for fuel contaminated oil. Check for fuel saturation in EVAP canister purge. If full of fuel, check canister control and hoses. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

Check for an intermittent TP sensor output that will cause system to go rich due to false indication of throttle moving. Check for false rich indication due to silicone contamination of HO2S indicated by DTC accompanied by lean driveability conditions and a powdery white deposit on sensor.

Check for internally shorted HO2S as indicated by a voltage of greater than one volt on scan tool. Disconnect HO2S. If voltage changes from greater than one volt to about .45 volt, replace HO2S. DO NOT solder HO2S wires.

DTC P0146 - HO2S INSUFFICIENT ACTIVITY BANK 1, SENSOR 3

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S or HO2S circuit is open.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.
10. Engine run time is greater than 2 minutes.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Connect scan tool. Warm engine to normal operating temperature. Run engine at greater than 1200 RPM for 2 minutes. If scan tool indicates closed loop, go to step 5). If scan tool does not indicate closed loop, go to next step.
3. Turn ignition off. Disconnect HO2S harness connector. Connect jumper wires between ground, and HO2S ground and HO2S signal circuits of HO2S connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is less than 0.2 volt, go to step 7). If HO2S voltage is not less than 0.2 volt, go to next step.
4. Remove jumper wires and reconnect HO2S connector. Turn ignition off. Disconnect Blue VCM connector. Using test light, probe VCM connector HO2S signal circuit to battery voltage. If test light illuminates, go to step 6). If test light does not illuminate, go to step 9).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in HO2S signal circuit. If signal circuit is open, go to step 11). If circuit is okay, go to step 8).
7. Check for poor connection at HO2S. If connection to HO2S is faulty, go to step 11). If connection is okay, go to step 10).
8. Check for poor connection at VCM connector. If connection is faulty, go to step 11). If connection is okay, go to step 12).
9. Repair open in HO2S ground circuit. After repairs, go to step 13).
10. Replace HO2S. After replacing sensor, go to step 13).
11. Repair circuit as necessary. After repairs, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0146. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

With ignition on and engine off, HO2S voltage on scan tool should gradually decrease to less than .15 volt indicating heater is operating properly. If voltage does not decrease as specified, disconnect HO2S connector and connect a test light between HO2S connector terminals "C" and "D" (engine harness side). If test light illuminates, replace HO2S. If test light does not illuminate, repair open in HO2S heater ground circuit or HO2S ignition feed circuit.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage of greater than .6 volt and less than .3 volt, to a fixed voltage of about .45 volt. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

DTC P0147 - HO2S HEATER CIRCUIT BANK 1, SENSOR 3

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC test determines if HO2S heater is operating properly by monitoring amount of time necessary for HO2S to become active after start-up.

1. System voltage is greater than 9 volts but less than 17 volts.
2. MAF is less than 27 gm/s.
3. Engine run time is greater than 2 seconds.
4. Engine coolant temperature is less than 90°F (32°C).
5. Intake air temperature is less than 90°F (32°C).
6. Difference between engine coolant temperature and intake air temperature is not greater than 41°F (5°C).

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage gradually decreases by .15 volt, go to step 5). If HO2S voltage does not gradually decrease by .15 volt, go to next step.
3. Turn ignition off. Disconnect HO2S connector. Using test light, probe HO2S connector terminal "D" (engine harness side) to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 6).
4. Connect test light between terminals "C" and "D" of HO2S connector (engine harness side). If test light illuminates, go to step 7). If test light does not illuminate, go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in HO2S Bank 1, Sensor 3 fuse. If fuse is open, go to step 14). If fuse is not open, go to step 9).
7. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 15).
8. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 10).
9. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 11).
10. Repair open in HO2S heater ground circuit. After repairs, go to step 16).
11. Check for open in HO2S ignition feed circuit. After repairs, go to step 13).
12. Repair poor connection. After repairs, go to step 16).
13. Repair open in HO2S ignition feed circuit. After repairs, go to step 16).
14. Repair short to ground in HO2S ignition feed circuit and replace fuse. After repairs, go to step 16).
15. Replace HO2S. After replacing sensor, go to next step.
16. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0147. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. DO NOT solder HO2S wires.

DTC P0151 - HO2S CIRCUIT LOW VOLTAGE BANK 2, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0151, DTC P0152, an open sensor circuit or a cold sensor causes open loop operation.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S voltage using scan tool. If HO2S voltage is less than .086 volt, go to next step. If HO2S voltage is not less than .086 volt, go to step 4).
3. Turn ignition off. Disconnect HO2S connector. Connect a jumper wire between HO2S ground circuit of HO2S connector (VCM side) and ground. Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is .35-.55 volt, go to step 7). If HO2S voltage is not .35-.55 volt, go to step 5).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Check for short to ground in HO2S signal circuit. If a problem is found, go to next step. If a problem is not found, go to step 8).
6. Repair circuit as necessary. After repairs, go to step 9).
7. See DIAGNOSTIC AIDS.
8. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0151. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Using scan tool, observe Long Term (LT) fuel trim values at different RPM and air flow conditions. Scan tool should display fuel trim cells so that LT fuel trim values can be check in each cell to determine when DTC may have set. If DTC is set, LT fuel trim values will be about 158 or greater.

Check for mispositioned HO2S wire pigtail contacting exhaust manifold. Check for intermittent ground in wire between connector and sensor. Check for poor VCM to engine block ground. Check for lean fuel injectors. Check for water near in-tank fuel pump inlet that may be delivered to injectors. Water causes a lean exhaust and can cause DTC to set.

System will be lean if fuel pressure is too low. Monitor fuel pressure while driving vehicle at various speeds and loads to verify pressure. Check for an exhaust leak that can cause outside air to be pulled into exhaust and past sensor. Check for vacuum or crankcase leaks that can cause a lean condition and possibly high idle. If all above checks are okay, HO2S is faulty. DO NOT solder HO2S wires.

DTC P0152 - HO2S CIRCUIT HIGH VOLTAGE BANK 2, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316C). DTC P0151, DTC P0152, an open sensor circuit or a cold sensor causes open loop operation. DTC P0152 determines if HO2S or circuit is shorted high by checking for a rich condition during steady throttle.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S voltage using scan tool. If HO2S voltage is not fixed at greater than .976 volt, go to next step. If HO2S voltage is not fixed at greater than .976 volt, go to step 4).
3. Turn ignition off. Disconnect HO2S connector. Connect jumper wires between ground, and HO2S ground and HO2S signal circuits of HO2S connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If voltage is less than .2 volt, go to step 5). If HO2S voltage is not less than .2 volt, go to step 6).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. See DIAGNOSTIC AIDS.
6. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0152. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

System will be rich if fuel pressure is too high. VCM can compensate for some increase in fuel pressure, but if pressure is too high, DTC may set. Check for rich or leaking injector. Check for fuel contaminated oil. Check for fuel saturation in EVAP canister purge. If full of fuel, check canister control and hoses. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

Check for an intermittent TP sensor output that will cause system to go rich due to false indication of throttle moving. Check for false rich indication due to silicone contamination of HO2S indicated by DTC accompanied by lean driveability conditions and a powdery white deposit on sensor.

Check for internally shorted HO2S as indicated by a voltage of greater than one volt on scan tool. Disconnect HO2S. If voltage changes from greater than one volt to about .45 volt, replace HO2S. DO NOT solder HO2S wires.

DTC P0153 - HO2S SLOW RESPONSE BANK 2, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. VCM monitors activity for 100 seconds after closed loop. During monitored period, VCM counts how often HO2S switches between rich and lean. VCM determines average switching time. If average switching time is too slow, DTC P0153 will set.

HO2S produces no voltage and acts as an open circuit when temperature is less than 600F (316C). HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S is operating properly by checking response time.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.
10. HO2S transition time from lean to rich or rich to lean is greater than 100 milliseconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other HO2S DTCs are set. If any other HO2S DTCs are set, go to applicable DTC test. If no other HO2S DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is not greater than 4 volts, go to next step.
4. Visually inspect exhaust system near HO2S for leaks. If a problem was found, go to step 8). If a problem was not found, go to next step.
5. Visually inspect if HO2S was properly installed. If a problem was found, go to step 8). If a problem was not found, go to next step.
6. Check if HO2S connection is contacting engine or exhaust system. If a problem was found, go to step 8). If a problem was not found, go to next step.
7. Remove HO2S and inspect for silicone contamination (a white powdery deposit on portion of sensor exposed to exhaust stream). Also, inspect for engine oil/coolant or lead contamination. If contamination is found, go to step 9). If contamination is not found, see DIAGNOSTIC AIDS.
8. Repair as necessary. After repairs, go to step 11).
9. Repair source of contamination. After repairs, go to next step.
10. Replace HO2S. After replacing sensor, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0153. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check HO2S heater operation. DO NOT solder HO2S wires.

DTC P0154 - HO2S INSUFFICIENT ACTIVITY BANK 2, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600F (316C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S or HO2S circuit is open.

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No MAF sensor DTCs are set.
7. No intrusive test is in progress.
8. No device controls are active.
9. System voltage is at least 9 volts.
10. Engine run time is greater than 2 minutes.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Connect scan tool. Warm engine to normal operating temperature. Run engine at greater than 1200 RPM for 2 minutes. If scan tool indicates closed loop, go to step 5). If scan tool does not indicate closed loop, go to next step.
3. Turn ignition off. Disconnect HO2S connector. Connect jumper wires between ground, and HO2S ground and HO2S signal circuits of HO2S connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is less than .2 volt, go to step 7). If HO2S voltage is not less than .2 volt, go to next step.
4. Remove jumper wires and reconnect HO2S connector. Turn ignition off. Disconnect Blue VCM connector. Using test light, probe VCM connector HO2S signal circuit to battery voltage. If test light illuminates, go to step 6). If test light does not illuminate, go to step 9).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in HO2S signal circuit. If a problem is found, go to step 11). If a problem is not found, go to step 8).
7. Check for poor connection at HO2S. If connection is faulty, go to step 11). If connection is okay, go to step 10).
8. Check for poor connection at VCM. If connection is faulty, go to step 11). If connection is okay, go to step 12).
9. Repair open in HO2S ground circuit. After repairs, go to step 13).
10. Replace HO2S. After replacing sensor, go to step 13).
11. Repair circuit as necessary. After repairs, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0154. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

With ignition on and engine off, HO2S voltage on scan tool should gradually decrease to less than .15 volt indicating heater is operating properly. If voltage does not decrease as specified, disconnect HO2S connector and connect a test light between HO2S connector terminals "C" and "D" (engine harness side). If test light illuminates, replace HO2S. If test light does not illuminate, repair open in HO2S heater ground circuit or HO2S ignition feed circuit.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage of greater than .6 volt and less than .3 volt, to a fixed voltage of about .45 volt. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

DTC P0155 - HO2S HEATER CIRCUIT BANK 2, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S heater is operating properly by monitoring amount of time necessary for HO2S to become active after start-up.

1. System voltage is greater than 9 volts but less than 17 volts.
2. MAF is less than 27 gm/s.
3. Engine run time is greater than 2 seconds.
4. Engine coolant temperature is less than 90°F (32°C).
5. Intake air temperature is less than 90°F (32°C).
6. Difference between engine coolant temperature and intake air temperature is less than 41°F (5°C).
7. Difference between engine coolant temperature and intake air temperature is less than 47°F (8°C).
8. Elapsed time to obtain .3-.6 volt is greater than calculated value.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage gradually decreases by .15 volt, go to step 5). If HO2S voltage does not gradually decrease by .15 volt, go to next step.
3. Turn ignition off. Disconnect HO2S connector. Using test light, probe HO2S connector terminal "D" (engine harness side) to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 6).
4. Connect test light between terminals "C" and "D" of HO2S connector (engine harness side). If test light illuminates, go to step 7). If test light does not illuminate, go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in 20-amp ENG-1 fuse. If fuse is open, go to step 14). If fuse is not open, go to step 9).
7. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 15).
8. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 10).
9. Check for poor connection at HO2S. If a problem was found, go to step 12). If a problem was not found, go to step 11).
10. Repair open in HO2S heater ground circuit. After repairs, go to step 16).
11. Check for open in HO2S ignition feed circuit. If circuit is open, go to step 13).
12. Repair poor connection. After repairs, go to step 16).
13. Repair open in HO2S ignition feed circuit. After repairs, go to step 16).
14. Repair short to ground in HO2S ignition feed circuit and replace fuse. After repairs, go to step 16).
15. Replace HO2S. After replacing sensor, go to next step.
16. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0155. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. DO NOT solder HO2S wires.

DTC P0171 - FUEL TRIM SYSTEM LEAN BANK 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

A "closed loop" air/fuel metering system is utilized for driveability, fuel economy and emission control. While in closed loop, VCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change in fuel delivery can be monitored using a scan tool and is indicated by Long Term (LT) and Short Term (ST) fuel trim values. Ideal fuel trim is about 128. If a lean condition is present, VCM will increase fuel, resulting in a fuel trim value greater than 128. If a rich condition is present, VCM will reduce fuel, resulting in a fuel trim value less than 128. DTC will set if an excessively lean condition is detected.

1. No IAC DTCs are set.
2. No HO2S DTCs are set.
3. No TP sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No EGR DTCs are set.
6. No EVAP DTCs are set.
7. No ECT sensor DTCs are set.
8. No MAF sensor DTCs are set.
9. No IAT sensor DTCs are set.
10. No VSS DTCs are set.
11. No system voltage DTCs are set.
12. No misfire DTCs are set.
13. Throttle position is less than 69.9 percent.
14. Engine speed is greater than 575 RPM but less than 4500 RPM.
15. BARO is greater than 70 kPa.
16. Engine coolant temperature is greater than 32°F (0°C) but less than 208F (98C).
17. Manifold absolute pressure is greater than 20 kPa but less than 98.9 kPa.
18. Intake air temperature is greater than -4°F (-20°C) but less than 158°F (70°C).
19. Airflow greater than 3 gm/s but less than 150 gm/s.
20. Vehicle speed is less than 85 MPH.
21. Average short term fuel trim is less than 115.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check for the following conditions: Exhaust system for corrosion, loose or missing hardware. HO2S is securely installed and pigtail is not contacting exhaust manifold or ignition wiring. Vacuum hoses for splits, kinks and proper connections. Throttle body, intake manifold and EGR for vacuum leaks. IAC, if a high or unsteady idle is being experienced. Crankcase ventilation valve, spring and "O" ring for proper installation. Fuel for excessive water, alcohol or other contaminants. VCM and sensor ground are clean, tight and in proper locations. If a problem was found, go to step 8). If a problem was not found, go to next step.
3. Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition on greater than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (4.2-4.8 kg/cm 2 ). On SFI models, pressure should be 56-62 psi (3.9-4.4 kg/cm 2 ). On all models, when pump stops, pressure may slightly vary, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 11).
4. Start and idle engine at normal operating temperature. If pressure decreases by 3-10 psi (.2-.7 kg/cm 2 ), go to next step. If pressure does not decrease by 3-10 psi (.2-.7 kg/cm 2 ), go to step 11).
5. Perform injector balance test. See the SYSTEM/COMPONENT TESTS article. If a problem was found, go to step 9). If a problem was not found, go to next step.
6. Perform canister purge solenoid check. See the SYSTEM/COMPONENT TESTS article. If a problem was found, go to next step. If a problem was not found, see DIAGNOSTIC AIDS.
7. Repair EVAP system. Install scan tool. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to step 10). If values are not as specified, see DIAGNOSTIC AIDS.
8. Repair problem as necessary. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to step 10). If values are not as specified, go to step 3).
9. Replace fuel injector. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to next step. If values are not as specified, go to step 6).
10. Lean condition is not present. See the TESTS W/O CODES article.
11. Diagnose fuel system. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. Go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0171. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

If problem can not be isolated during diagnostic procedures, monitor LT fuel trim value while operating vehicle under various load conditions. A condition that causes DTC P0300 may also result in DTC P0171 setting. Also, an extreme lean condition that may cause DTC P0171 to set may result in P0300 setting due to misfire at idle. If cause for DTC P0171 cannot be determined and DTC P0300 is also set, go to DTC P0300 .

DTC P0172 - FUEL TRIM SYSTEM RICH BANK 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

A "closed loop" air/fuel metering system is utilized for driveability, fuel economy and emission control. While in closed loop, VCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change in fuel delivery can be monitored using a scan tool and is indicated by Long Term (LT) and Short Term (ST) fuel trim values. Ideal fuel trim is about 128. If a lean condition is present, VCM will increase fuel, resulting in a fuel trim value greater than 128. If a rich condition is present, VCM will reduce fuel, resulting in a fuel trim value less than 128. DTC will set if an excessively rich condition is detected.

1. No IAC DTCs are set.
2. No HO2S DTCs are set.
3. No TP sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No EGR DTCs are set.
6. No EVAP DTCs are set.
7. No ECT sensor DTCs are set.
8. No MAF sensor DTCs are set.
9. No IAT sensor DTCs are set.
10. No VSS DTCs are set.
11. No system voltage DTCs are set.
12. No misfire DTCs are set.
13. Throttle position is less than 69.9 percent.
14. Engine speed is greater than 575 RPM but less than 4500 RPM.
15. BARO is greater than 70 kPa.
16. ECT is greater than 32°F (0°C) but less than 208°F (98°C).
17. MAP is greater than 20 kPa but less than 98.9 kPa.
18. IAT is greater than -4°F (-20°C) but less than 158°F (70°C).
19. Airflow greater than 3 gm/s but less than 150 gm/s.
20. Vehicle speed is less than 85 MPH.
21. Average short term fuel trim is less than 115.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check for the following conditions: Air intake duct collapsed or restricted. Air filter plugged. Throttle body coking or objects blocking IAC passage, if a low or unsteady idle is being experienced. Fuel pressure regulator for proper operation. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. TP sensor for loose or missing mounting bolts. Monitor TP sensor voltage using scan tool while slowly opening throttle. Voltage should increase steadily and evenly from closed throttle voltage (.5 volt) to wide open throttle voltage (4.5 volts). If voltage is not as specified, replace TP sensor. If a problem was found, go to step 8). If a problem was not found, go to next step.
3. Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition on more than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ). On SFI models, pressure should be 56-62 psi (3.9-4.4 kg/cm 2 ). On all models, when pump stops, pressure may slightly vary, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 11).
4. Perform injector balance test. See the SYSTEM/COMPONENT TESTS article. If a problem was found, go to step 9). If a problem was not found, go to next step.
5. Remove HO2S and inspect for silicone contamination (a white powdery deposit on portion of sensor exposed to exhaust stream). If contamination is found, go to step 12). If contamination is not found, go to next step.
6. Perform canister purge solenoid check. See the SYSTEM/COMPONENT TESTS article. If a problem was found, go to next step. If a problem was not found, see DIAGNOSTIC AIDS.
7. Repair EVAP system. Install scan tool. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to step 10). If values are not as specified, see DIAGNOSTIC AIDS.
8. Repair problem as necessary. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to step 10). If values are not as specified, go to step 3).
9. Replace fuel injector. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to next step. If values are not as specified, go to step 5).
10. Rich condition is not present. See the TESTS W/O CODES article.
11. Diagnose fuel system. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After repairs, go to step 13).
12. Replace HO2S. After replacing sensor, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0172. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

If problem can not be isolated during diagnostic procedures, monitor LT fuel trim value while operating vehicle under various load conditions. A condition that causes DTC P0300 may also result in DTC P0172 setting. Also, an extreme rich condition that may cause DTC P0172 to set may result in P0300 setting due to misfire at idle. If cause for DTC P0172 can not be determined and DTC P0300 is also set, go to DTC P0300 .

DTC P0174 - FUEL TRIM SYSTEM LEAN BANK 2

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

A "closed loop" air/fuel metering system is utilized for driveability, fuel economy and emission control. While in closed loop, VCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change in fuel delivery can be monitored using a scan tool and is indicated by Long Term (LT) and Short Term (ST) fuel trim values. Ideal fuel trim is about 128. If a lean condition is present, VCM will increase fuel, resulting in a fuel trim value greater than 128. If a rich condition is present, VCM will reduce fuel, resulting in a fuel trim value less than 128. DTC will set if an excessively lean condition is detected.

1. No IAC DTCs are set.
2. No HO2S DTCs are set.
3. No TP sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No EGR DTCs are set.
6. No EVAP DTCs are set.
7. No ECT sensor DTCs are set.
8. No misfire DTCs are set.
9. Throttle position is less than 69.9 percent.
10. Engine speed is greater than 575 RPM but less than 4500 RPM.
11. BARO is greater than 70 kPa.
12. ECT is greater than 32°F (0°C) but less than 208°F (98°C).
13. MAP is greater than 20 kPa but less than 98.9 kPa.
14. IAT is greater than -4°F (-20°C) but less than 158°F (70°C).
15. Airflow greater than 3 gm/s but less than 150 gm/s.
16. Vehicle speed is less than 85 MPH.
17. Average short term fuel trim is not greater than 115.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check for the following conditions: Exhaust system for corrosion, loose or missing hardware. HO2S is securely installed and pigtail is not contacting exhaust manifold or ignition wiring. Vacuum hoses for splits, kinks and proper connections. Throttle body, intake manifold and EGR for vacuum leaks. IAC, if a high or unsteady idle is being experienced. Crankcase ventilation valve, spring and "O" ring for proper installation. Fuel for excessive water, alcohol or other contaminants. VCM and sensor ground are clean, tight and in proper locations. If a problem was found, go to step 8). If a problem was not found, go to next step.
3. Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition on more than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (4.2-4.6 kPa). On SFI models, pressure should be 56-62 psi (3.9-4.4 kPa). On all models, when pump stops, pressure may slightly vary, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 11).
4. Start and idle engine at normal operating temperature. If pressure decreases by 3-10 psi (.2-.7 kg/cm 2 ), go to next step. If pressure does not decrease by 3-10 psi (.2-.7 kg/cm 2 ), go to step 11).
5. Perform injector balance test. See the SYSTEM/COMPONENT TESTS article. If a problem was found, go to step 9). If a problem was not found, go to next step.
6. Perform canister purge solenoid check. See the SYSTEM/COMPONENT TESTS article. If a problem was found, go to next step. If a problem was not found, see DIAGNOSTIC AIDS.
7. Repair EVAP system. Install scan tool. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to step 10). If values are not as specified, see DIAGNOSTIC AIDS.
8. Repair problem as necessary. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to step 10). If values are not as specified, go to step 3).
9. Replace fuel injector. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to next step. If values are not as specified, go to step 6).
10. Lean condition is not present. See the TESTS W/O CODES article.
11. Diagnose fuel system. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. Go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0174. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

If problem can not be isolated during diagnostic procedures, monitor LT fuel trim value while operating vehicle under various load conditions. A condition that causes DTC P0300 may also result in DTC P0174 setting. Also, an extreme lean condition that may cause DTC P0174 to set may result in P0300 setting due to misfire at idle. If cause for DTC P0174 can not be determined and DTC P0300 is also set, go to DTC P0300 .

DTC P0175 - FUEL TRIM SYSTEM RICH BANK 2

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

A "closed loop" air/fuel metering system is utilized for driveability, fuel economy and emission control. While in closed loop, VCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change in fuel delivery can be monitored using a scan tool and is indicated by Long Term (LT) and Short Term (ST) fuel trim values. Ideal fuel trim is about 128. If a lean condition is present, VCM will increase fuel, resulting in a fuel trim value greater than 128. If a rich condition is present, VCM will reduce fuel, resulting in a fuel trim value less than 128. DTC will set if an excessively rich condition is detected.

1. No IAC DTCs are set.
2. No HO2S DTCs are set.
3. No TP sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No EGR DTCs are set.
6. No EVAP DTCs are set.
7. No ECT sensor DTCs are set.
8. No MAF sensor DTCs are set.
9. No misfire DTCs are set.
10. Throttle position is less than 69.9 percent.
11. Engine speed is greater than 575 RPM but less than 4500 RPM.
12. BARO is greater than 70 kPa.
13. ECT is greater than 32°F (0°C) but less than 208°F (98°C).
14. MAP is greater than 20 kPa but less than 98.9 kPa.
15. IAT is greater than -4°F (-20°C) but less than 158°F (70°C).
16. Air flow greater than 3 gm/s but less than 150 gm/s.
17. Vehicle speed is less than 85 MPH.
18. Average short term fuel trim is less than 115.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check for the following conditions: Air intake duct collapsed or restricted. Air filter plugged. Throttle body coking or objects blocking IAC passage, if a low or unsteady idle is being experienced. Fuel pressure regulator for proper operation. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. TP sensor for loose or missing mounting bolts. Monitor TP sensor voltage using scan tool while slowly opening throttle. Voltage should increase steadily and evenly from closed throttle voltage (.5 volt) to wide open throttle voltage (4.5 volts). If voltage is not as specified, replace TP sensor. If a problem was found, go to step 8). If a problem was not found, go to next step.
3. Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition on more than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (415-455 kPa). On SFI models, pressure should be 56-62 psi (385-430 kPa). On all models, when pump stops, pressure may slightly vary, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 11).
4. Perform injector balance test. See the SYSTEM/COMPONENT TESTS article. If a problem was found, go to step 9). If a problem was not found, go to next step.
5. Remove HO2S and inspect for silicon contamination (a white powdery deposit on portion of sensor exposed to exhaust stream). If contamination is found, go to step 12). If contamination is not found, go to next step.
6. Perform canister purge solenoid check. See the SYSTEM/COMPONENT TESTS article. If a problem was found, go to next step. If a problem was not found, see DIAGNOSTIC AIDS.
7. Repair EVAP system. Install scan tool. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to step 10). If values are not as specified, see DIAGNOSTIC AIDS.
8. Repair problem as necessary. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to step 10). If values are not as specified, go to step 3).
9. Replace fuel injector. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to next step. If values are not as specified, go to step 5).
10. Rich condition is not present. See the TESTS W/O CODES article.
11. Diagnose fuel system. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After repairs, go to step 13).
12. Replace HO2S. After replacing sensor, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0175. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

If problem can not be isolated during diagnostic procedures, monitor LT fuel trim value while operating vehicle under various load conditions. A condition that causes DTC P0300 may also result in DTC P0175 setting. Also, an extreme rich condition that may cause DTC P0175 to set may result in P0300 setting due to misfire at idle. If cause for DTC P0175 cannot be determined and DTC P0300 is also set, go to DTC P0300 .

DTC P0300 - MISFIRE DETECTED

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft Position (CKP) sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. CKP sensor information is compared to engine speed and engine load to determine if a misfire occurred.

If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat the same, or if 3 or more cylinders are misfiring.

VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.

1. No TP sensor DTCs are set.
2. No MAF DTCs are set.
3. No IC control DTCs are set.
4. No VSS DTCs are set.
5. No crankshaft position sensor DTCs are set.
6. Rough road condition is not detected.
7. Engine coolant temperature is 20-203°F (-6.75 to 95°C).
8. Engine speed is 600-5600 RPM.
9. System voltage is 9-16 volts.
10. Positive throttle position change is less than 4.9 percent for 100 milliseconds.
11. Negative throttle position change is less than 2.9 percent for 100 milliseconds.
12. Misfire is detected.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is not greater than 4 volts, go to next step.
4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 10).
5. Using scan tool, review misfire index. If misfire index is increasing for more than one cylinder, see DIAGNOSTIC AIDS. If not, go to next step.
6. Install Spark Tester (J 26792) on spark plug wire No. 1. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. Repeat for each spark plug wire. If spark is adequate on all spark plug wires, go to next step. If spark is not adequate on all spark plug wires, go to step 11).
7. Inspect spark plugs for wear, excessive air gap, cracks or fouling. If spark plug are okay, go to next step. If spark plugs are not okay, go to step 12).
8. Perform a cylinder compression test. If a problem was found, go to step 14). If a problem was not found, go to next step.
9. Diagnose fuel injector circuit. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. If a problem was found, go to next step. If a problem was not found, go to step 13).
10. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
11. Perform enhanced ignition system check. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
12. Replace spark plugs. After replacing spark plugs, go to step 14).
13. Repair circuit as necessary. After repairs, go to step 14).
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0300. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for crossfiring. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.

DTC P0301 - CYLINDER NO. 1 MISFIRE DETECTED

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft position sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. Crankshaft position sensor information is compared to engine speed and engine load to determine if a misfire occurred.

If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat even or if 3 or more cylinders are misfiring.

VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.

1. No TP sensor DTCs are set.
2. No MAF DTCs are set.
3. No IC control DTCs are set.
4. No VSS DTCs are set.
5. No crankshaft position sensor DTCs are set.
6. Rough road condition is not detected.
7. ECT is greater than or equal to 19°F (-7°C).
8. Engine speed is 600-5600 RPM.
9. System voltage is 9-16 volts.
10. Positive throttle position change is less than 4.9 percent for 100 milliseconds.
11. Negative throttle position change is less than 2.9 percent for 100 milliseconds.
12. Misfire is detected.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is less than 4 volts, go to next step.
4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 9).
5. Install Spark Tester (J 26792) on spark plug wire No. 1. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. If spark is adequate, go to next step. If spark is not adequate, go to step 10).
6. Remove spark plug from affected cylinder. Inspect spark plugs for wear, excessive air gap, cracks or fouling. Swap spark plug with a plug from another cylinder that is not experiencing misfire. Monitor misfire index using scan tool. If misfire index increases for cylinder with suspect plug, go to next step. If misfire index does not increase for cylinder with suspect plug, go to step 11).
7. Perform a cylinder compression test. If a problem was found, go to step 13). If a problem was not found, go to next step.
8. Diagnose injector circuit. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. If a problem was found, go to next step. If a problem was not found, go to step 12).
9. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
10. Perform enhanced ignition system check. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
11. Replace spark plug. After replacing spark plugs, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Repair problem as necessary. After repairs, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for crossfiring. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.

DTC P0302 - CYLINDER NO. 2 MISFIRE DETECTED

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft position sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. Crankshaft position sensor information is compared to engine speed and engine load to determine if a misfire occurred.

If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat even or if 3 or more cylinders are misfiring.

VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.

1. No TP sensor DTCs are set.
2. No MAF DTCs are set.
3. No IC control DTCs are set.
4. No VSS DTCs are set.
5. No crankshaft position sensor DTCs are set.
6. Rough road condition is not detected.
7. ECT is greater than to equal to 19°F (-7°C).
8. Engine speed is 600-5600 RPM.
9. System voltage is 9-16 volts.
10. Positive throttle position change is less than 4.9 percent for 100 milliseconds.
11. Negative throttle position change is less than 2.9 percent for 100 milliseconds.
12. Misfire is detected.

1. Perform Powertrain On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is less than 4 volts, go to next step.
4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 9).
5. Install Spark Tester (J 26792) on spark plug wire No. 2. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. If spark is adequate, go to next step. If spark is not adequate, go to step 10).
6. Remove spark plug from affected cylinder. Inspect spark plugs for wear, excessive air gap, cracks or fouling. Swap spark plug with a plug from another cylinder that is not experiencing misfire. Monitor misfire index using scan tool. If misfire index increases for cylinder with suspect plug, go to next step. If misfire index does not increase for cylinder with suspect plug, go to step 11).
7. Perform a cylinder compression test. If a problem was found, go to step 13). If a problem was not found, go to next step.
8. Diagnose injector circuit. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. If a problem was found, go to next step. If a problem was not found, go to step 12).
9. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
10. Perform enhanced ignition system check. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
11. Replace spark plug. After replacing spark plug, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Repair problem as necessary. After repairs, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for crossfiring. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.

DTC P0303 - CYLINDER NO. 3 MISFIRE DETECTED

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft position sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. Crankshaft position sensor information is compared to engine speed and engine load to determine if a misfire occurred.

If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat even or if 3 or more cylinders are misfiring.

VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.

1. No TP sensor DTCs are set.
2. No MAF DTCs are set.
3. No IC control DTCs are set.
4. No VSS DTCs are set.
5. No crankshaft position sensor DTCs are set.
6. Rough road condition is not detected.
7. ECT is greater than or equal to 19°F (-7°C).
8. Engine speed is 600-5600 RPM.
9. System voltage is 9-16 volts.
10. Positive throttle position change is less than 4.9 percent for 100 milliseconds.
11. Negative throttle position change is less than 2.9 percent for 100 milliseconds.
12. Misfire is detected.

1. Perform Powertrain On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is less than 4 volts, go to next step.
4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 9).
5. Install Spark Tester (J 26792) on spark plug wire No. 3. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. If spark is adequate, go to next step. If spark is not adequate, go to step 10).
6. Remove spark plug from affected cylinder. Inspect spark plugs for wear, excessive air gap, cracks or fouling. Swap spark plug with a plug from another cylinder that is not experiencing misfire. Monitor misfire index using scan tool. If misfire index increases for cylinder with suspect plug, go to next step. If misfire index does not increase for cylinder with suspect plug, go to step 11).
7. Perform a cylinder compression test. If a problem was found, go to step 13). If a problem was not found, go to next step.
8. Diagnose injector circuit. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. If a problem was found, go to next step. If a problem was not found, go to step 12).
9. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
10. Perform enhanced ignition system check. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
11. Replace spark plug. After replacing spark plug, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Repair problem as necessary. After repairs, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for crossfiring. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.

DTC P0304 - CYLINDER NO. 4 MISFIRE DETECTED

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft position sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. Crankshaft position sensor information is compared to engine speed and engine load to determine if a misfire occurred.

If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat even or if 3 or more cylinders are misfiring.

VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.

1. No TP sensor DTCs are set.
2. No MAF DTCs are set.
3. No IC control DTCs are set.
4. No VSS DTCs are set.
5. No crankshaft position sensor DTCs are set.
6. Rough road condition is not detected.
7. ECT is greater than or equal to 19°F (-7°C).
8. Engine speed is 600-5600 RPM.
9. System voltage is 9-16 volts.
10. Positive throttle position change is less than 4.9 percent for 100 milliseconds.
11. Negative throttle position change is less than 2.9 percent for 100 milliseconds.
12. Misfire is detected.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is less than 4 volts, go to next step.
4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 9).
5. Install Spark Tester (J 26792) on spark plug wire No. 4. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. If spark is adequate, go to next step. If spark is not adequate, go to step 10).
6. Remove spark plug from affected cylinder. Inspect spark plugs for wear, excessive air gap, cracks or fouling. Swap spark plug with a plug from another cylinder that is not experiencing misfire. Monitor misfire index using scan tool. If misfire index increases for cylinder with suspect plug, go to next step. If misfire index does not increase for cylinder with suspect plug, go to step 11).
7. Perform a cylinder compression test. If a problem was found, go to step 13). If a problem was not found, go to next step.
8. Diagnose injector circuit. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. If a problem was found, go to next step. If a problem was not found, go to step 12).
9. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
10. Perform enhanced ignition system check. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
11. Replace spark plug. After replacing spark plugs, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Repair problem as necessary. After repairs, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for crossfiring. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.

DTC P0305 - CYLINDER NO. 5 MISFIRE DETECTED

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft position sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. Crankshaft position sensor information is compared to engine speed and engine load to determine if a misfire occurred.

If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat even or if 3 or more cylinders are misfiring.

VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.

1. No TP sensor DTCs are set.
2. No MAF DTCs are set.
3. No IC control DTCs are set.
4. No VSS DTCs are set.
5. No crankshaft position sensor DTCs are set.
6. Rough road condition is not detected.
7. ECT is greater than or equal to 19°F (-7°C).
8. Engine speed is 600-5600 RPM.
9. System voltage is 9-16 volts.
10. Positive throttle position change is less than 4.9 percent for 100 milliseconds.
11. Negative throttle position change is less than 2.9 percent for 100 milliseconds.
12. Misfire is detected.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is less than 4 volts, go to next step.
4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 9).
5. Install Spark Tester (J 26792) on spark plug wire No. 5. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. If spark is adequate, go to next step. If spark is not adequate, go to step 10).
6. Remove spark plug from affected cylinder. Inspect spark plugs for wear, excessive air gap, cracks or fouling. Swap spark plug with a plug from another cylinder that is not experiencing misfire. Monitor misfire index using scan tool. If misfire index increases for cylinder with suspect plug, go to next step. If misfire index does not increase for cylinder with suspect plug, go to step 11).
7. Perform a cylinder compression test. If a problem was found, go to step 13). If a problem was not found, go to next step.
8. Diagnose fuel injector circuit. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. If a problem was found, go to next step. If a problem was not found, go to step 12).
9. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
10. Perform enhanced ignition system check. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
11. Replace spark plug. After repairs, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Repair problem as necessary. After repairs, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for crossfiring. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.

DTC P0306 - CYLINDER NO. 6 MISFIRE DETECTED

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft position sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. Crankshaft position sensor information is compared to engine speed and engine load to determine if a misfire occurred.

If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat even or if 3 or more cylinders are misfiring.

VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.

1. No TP sensor DTCs are set.
2. No MAF DTCs are set.
3. No IC control DTCs are set.
4. No VSS DTCs are set.
5. No crankshaft position sensor DTCs are set.
6. Rough road condition is not detected.
7. ECT is greater than or equal to 19°F (-7°C).
8. Engine speed is 600-5600 RPM.
9. System voltage is 9-16 volts.
10. Positive throttle position change is less than 4.9 percent for 100 milliseconds.
11. Negative throttle position change is less than 2.9 percent for 100 milliseconds.
12. Misfire is detected.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is less than 4 volts, go to next step.
4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 9).
5. Install Spark Tester (J 26792) on spark plug wire No. 6. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. If spark is adequate, go to next step. If spark is not adequate, go to step 10).
6. Remove spark plug from affected cylinder. Inspect spark plugs for wear, excessive air gap, cracks or fouling. Swap spark plug with a plug from another cylinder that is not experiencing misfire. Monitor misfire index using scan tool. If misfire index increases for cylinder with suspect plug, go to next step. If misfire index does not increase for cylinder with suspect plug, go to step 11).
7. Perform a cylinder compression test. If a problem was found, go to step 13). If a problem was not found, go to next step.
8. Diagnose injector circuit. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. If a problem was found, go to next step. If a problem was not found, go to step 12).
9. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
10. Perform enhanced ignition system check. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
11. Replace spark plug. After replacing spark plugs, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Repair problem as necessary. After repairs, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for crossfiring. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.

DTC P0307 - CYLINDER NO. 7 MISFIRE DETECTED

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft position sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. Crankshaft position sensor information is compared to engine speed and engine load to determine if a misfire occurred.

If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat even or if 3 or more cylinders are misfiring.

VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.

1. No TP sensor DTCs are set.
2. No MAF DTCs are set.
3. No IC control DTCs are set.
4. No VSS DTCs are set.
5. No crankshaft position sensor DTCs are set.
6. Rough road condition is not detected.
7. ECT is greater than or equal to 19°F (-7°C).
8. Engine speed is 600-5600 RPM.
9. System voltage is 9-16 volts.
10. Positive throttle position change is less than 4.9 percent for 100 milliseconds.
11. Negative throttle position change is less than 2.9 percent for 100 milliseconds.
12. Misfire is detected.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is less than 4 volts, go to next step.
4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 9).
5. Install Spark Tester (J 26792) on spark plug wire No. 7. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. If spark is adequate, go to next step. If spark is not adequate, go to step 10).
6. Remove spark plug from affected cylinder. Inspect spark plugs for wear, excessive air gap, cracks or fouling. Swap spark plug with a plug from another cylinder that is not experiencing misfire. Monitor misfire index using scan tool. If misfire index increases for cylinder with suspect plug, go to next step. If misfire index does not increase for cylinder with suspect plug, go to step 11).
7. Perform a cylinder compression test. If a problem was found, go to step 13). If a problem was not found, go to next step.
8. Diagnose injector circuit. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. If a problem was found, go to next step. If a problem was not found, go to step 12).
9. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
10. Perform enhanced ignition system check. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
11. Replace spark plug. After replacing spark plugs, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Repair problem as necessary. After repairs, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for crossfiring. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.

DTC P0308 - CYLINDER NO. 8 MISFIRE DETECTED

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft position sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. Crankshaft position sensor information is compared to engine speed and engine load to determine if a misfire occurred.

If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat even or if 3 or more cylinders are misfiring.

VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.

1. No TP sensor DTCs are set.
2. No MAF DTCs are set.
3. No IC control DTCs are set.
4. No VSS DTCs are set.
5. No crankshaft position sensor DTCs are set.
6. Rough road condition is not detected.
7. ECT is greater than or equal to 19°F (-7°C).
8. Engine speed is 600-5600 RPM.
9. System voltage is 9-16 volts.
10. Positive throttle position change is less than 4.9 percent for 100 milliseconds.
11. Negative throttle position change is less than 2.9 percent for 100 milliseconds.
12. Misfire is detected.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is less than 4 volts, go to next step.
4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 9).
5. Install Spark Tester (J 26792) on spark plug wire No. 8. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. If spark is adequate, go to next step. If spark is not adequate, go to step 10).
6. Remove spark plug from affected cylinder. Inspect spark plugs for wear, excessive air gap, cracks or fouling. Swap spark plug with a plug from another cylinder that is not experiencing misfire. Monitor misfire index using scan tool. If misfire index increases for cylinder with suspect plug, go to next step. If misfire index does not increase for cylinder with suspect plug, go to step 11).
7. Perform a cylinder compression test. If a problem was found, go to step 13). If a problem was not found, go to next step.
8. Diagnose fuel injector circuit. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. If a problem was found, go to next step. If a problem was not found, go to step 12).
9. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
10. Perform enhanced ignition system check. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
11. Replace spark plug. After replacing spark plug, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Repair problem as necessary. After repairs, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for crossfiring. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.

DTC P0325 - KNOCK SENSOR MODULE CIRCUIT

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM utilizes knock sensors to detect engine detonation, allowing VCM to retard Ignition Control (IC) spark timing based on knock sensor signal received. Knock Sensor (KS) circuitry within sensor pulls down VCM-supplied 5-volt DC signal, so that under a no-knock condition signal on KS, circuit measures about 1.3 volts. Sensor produces an AC signal that rides on DC signal. Signal amplitude and frequency are dependent upon amount of knock experienced.

VCM contains a replaceable KS module. KS module contains circuitry that allows VCM to utilize KS signal and diagnose knock sensors and circuitry. VCM will set DTC if KS module is missing or faulty causing a continuous knock condition.

1. DTC P0327 is not set.
2. Engine has been running for at least 120 seconds.
3. System voltage is greater than 10 volts but less than 17.1 volts.
4. VCM detects a problem with KS module circuitry that causes a continuous knock condition.
5. Conditions are present for up to .5 second.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. If engine knock can be heard, repair mechanical problem before proceeding. Install scan tool. Operate vehicle within the conditions for setting this DTC. Using scan tool, monitor SPECIFIC DTC for DTC P0325. If scan tool indicates DTC P0325 FAILED THIS IGN?, go to step 4). If scan tool does not indicate DTC P0325 FAILED THIS IGN?, go to next step.
3. Turn ignition on, with engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC for DTC P0325. If scan tool indicates DTC P0325 FAILED THIS IGN?, go to next step. If scan tool does not indicate DTC P0325 FAILED THIS IGN?, see DIAGNOSTIC AIDS.
4. Check KS signal circuit for incorrect routing near secondary wires and repair as necessary. If a problem was found, go to step 8). If a problem was not found, go to next step.
5. Check if KS module is fully seated or incorrectly installed and repair as necessary. If a problem was found, go to step 8). If a problem was not found, go to next step.
6. Replace KS module. Operate vehicle within the conditions for setting this DTC. Using scan tool, monitor SPECIFIC DTC for DTC P0325. If scan tool indicates DTC P0325 FAILED THIS IGN?, go to next step. If scan tool does not indicate DTC P0325 FAILED THIS IGN?, go to step 8).
7. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
8. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0325. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
9. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check for poor connections at VCM. Inspect KS module connector for backed out terminals, broken locks, and improperly formed or damaged terminals. Check for damaged or improperly installed KS module. Check for bent pins, deformed terminals, or if KS module is fully seated. Check knock sensor torque specification. Specification should be 14 ft. lbs. (19 N.m). Checking FAIL RECORDS vehicle mileage data since diagnostic test last failed can be useful in determining how often condition causing DTC to set occurs. This may assist in diagnosis.

DTC P0327 - KNOCK SENSOR CIRCUIT LOW VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM utilizes knock sensors to detect engine detonation, allowing VCM to retard Ignition Control (IC) spark timing based on knock sensor signal received. Knock Sensor (KS) circuitry within sensor pulls down VCM-supplied 5-volt signal, so that under a no knock condition signal on KS circuit measures about 1.3 volts. Sensor produces an AC signal that rides on 1.3 volts DC. Signal amplitude and frequency are dependent upon amount of knock experienced.

VCM determines if knock is present by comparing signal level on KS circuit with voltage level on noise channel. Noise channel allows VCM to reject any false knock signal by indicating amount of normal engine mechanical noise present. Normal engine noise varies depending on engine speed and load. DTC will set when VCM determines that an abnormally high noise channel voltage level is being experienced. DTC will set when the following conditions are present

Knock sensor update test

1. Timing retard is less than zero degrees.
2. System voltage is greater than 10 volts but less than 17.1 volts.
3. Engine coolant temperature is greater than 140°F (60°C).
4. Engine run time is greater than 2 minutes.
5. Engine speed is 500-900 RPM.

Active noise channel test

1. No ETC sensor DTCs are set.
2. No ETC sensor DTCs are set.
3. Knock sensor update test is complete.
4. Engine coolant temperature is at least 140°F (60°C).
5. Engine speed is greater than or equal to 2000 RPM, but less than 10,000 RPM.
6. Throttle angle is greater than 5.8 percent.
7. Engine run time is at least 2 minutes.
8. System voltage is greater than 10 volts but greater than 17.1 volts.
9. Timing retard is not greater than zero degrees.
10. VCM is monitoring a ESC noise channel voltage level less than .5 volt.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Operate vehicle within the conditions for setting this DTC. Using scan tool, monitor SPECIFIC DTC for DTC P0327. If scan tool indicates DTC P0327 FAILED THIS IGN?, go to step 4). If scan tool does not indicate DTC P0327 FAILED THIS IGN?, go to next step.
3. Turn ignition on, with engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC for DTC P0327. If scan tool indicates DTC P0327 FAILED THIS IGN?, go to next step. If scan tool does not indicate DTC P0327 FAILED THIS IGN?, see DIAGNOSTIC AIDS.
4. Turn ignition off. Disconnect knock sensor connector. Turn ignition on, with engine off. Using DVOM, check voltage between KS signal circuit of knock sensor connector and ground. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 8).
5. Using DVOM, check resistance between knock sensor terminal and engine ground. If resistance is 100 k/ohms, go to next step. If resistance is not 100 k/ohms, go to step 12).
6. Using DVOM, check voltage between knock sensor terminal and engine ground. Tap on engine lift bracket while observing DVOM. If a signal is indicated while tapping bracket, go to next step. If a signal is not indicated while tapping bracket, go to step 9).
7. Check KS signal circuit for a poor connection at knock sensor and repair as necessary. If a problem was found, go to step 14). If a problem was not found, go to step 10).
8. Turn ignition off. Disconnect VCM connector. Turn ignition on. Check for open, short to voltage or short to ground in KS signal circuit between VCM and knock sensor. Repair as necessary. If a problem was found, go to step 14). If a problem was not found, go to step 10).
9. Replace knock sensor. After replacing sensor, go to step 14).
10. Turn ignition off. Disconnect VCM connector. Check KS signal circuit for a poor connection at VCM and repair as necessary. If a problem was found, go to step 14). If a problem was not found, go to next step.
11. Check if KS module is fully seated or incorrectly installed and repair as necessary. If a problem was found, go to step 14). If a problem was not found, go to next step.
12. Replace KS module. Operate vehicle within the conditions for setting this DTC. Using scan tool, monitor SPECIFIC DTC for DTC P0327. If scan tool indicates DTC P0327 FAILED THIS IGN?, go to next step. If scan tool does not indicate DTC P0327 FAILED THIS IGN?, go to step 14).
13. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0327. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check for poor connections at VCM. Inspect KS module connector for backed-out terminals, broken locks, and improperly formed or damaged terminals. Check for damaged or improperly installed KS module. Check for bent pins, deformed terminals, or if KS module is fully seated. Check knock sensor torque specification. Specification should be 14 ft. lbs. (19 N.m). Checking FAIL RECORDS vehicle mileage data since diagnostic test last failed can be useful in determining how often condition causing DTC to set occurs. This may assist in diagnosis.

DTC P0336 - CRANKSHAFT POSITION SENSOR CIRCUIT PERFORMANCE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft Position (CKP) sensor sends a reference signal to VCM indicating crankshaft position and RPM. Information is used to determine when to pulse ignition coil, fuel injectors and control ignition timing.

1. Engine cranking and VCM receives 4 or more camshaft position signals without crankshaft position signal.
2. Crankshaft position sensor signal is missing for at least .5 second.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Start and run vehicle. If vehicle starts and continues to run, see DIAGNOSTIC AIDS. If vehicle does not start and continue to run, go to next step.
3. Turn ignition off. Disconnect crankshaft position sensor connector. Turn ignition on, with engine off. Using test light, probe ignition feed circuit of crankshaft position sensor connector (engine harness side) to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 6).
4. Connect test light between ignition feed circuit and ground circuit of crankshaft position sensor connector (engine harness side). If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
5. Turn ignition off. Install Gray jumper wires from Connector Test Kit(J 35616-A) between engine harness connector and crankshaft position sensor. Set DVOM to duty cycle position. Connect DVOM between signal circuit and ground circuit of crankshaft position sensor connector (engine harness side). Crank engine. If duty cycle is less than 20-40 percent, go to step 8). If duty cycle is not as specified, go to step 10).
6. Repair open or short to ground in ignition feed circuit. After repairs, go to step 13).
7. Check for open in ground circuit. If an open was found, go to step 11). If a problem was not found, go to step 9).
8. With DVOM still connected, set DVOM to AC-volt scale. Crank engine. If voltage is greater than 10 volts, go to step 11). If voltage is less than 10 volts, go to next step.
9. Check for open in signal circuit or ground circuit. If circuit is open, go to step 11). If circuit is okay, go to step 12).
10. Replace crankshaft position sensor. Inspect sensor mounting surface and clean debris as necessary. After repairs, go to step 13).
11. Repair as necessary. After repairs, go to step 13).
12. Replace VCM. After replacing VCM, go to step 13).
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0336. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC is intermittent, see the TESTS W/O CODES article.

DTC P0337 - CRANKSHAFT POSITION SENSOR CIRCUIT LOW FREQUENCY

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft Position (CKP) sensor sends a reference signal to VCM indicating crankshaft position and RPM. Information is used to determine when to pulse ignition coil, fuel injectors and control ignition timing.

1. Engine speed is less than 4000 RPM.
2. MAF sensor is at least 5 gm/s.
3. Crank sensor duty cycle is greater than 50 percent (or the ratio high ref/low ref is less than 1.8).
4. Engine speed displayed on scan tool is 2400 RPM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Turn ignition off. Disconnect crankshaft position sensor connector. Turn ignition on, with engine off. Using test light, probe signal circuit of crankshaft position sensor connector (engine harness side) to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
3. Turn ignition off. Using test light, probe ground circuit of crankshaft position sensor connector (engine harness side) to battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
4. Disconnect Blue VCM connector. Using test light, probe ignition feed circuit of crankshaft position sensor connector (engine harness side) to battery voltage. If test light illuminates, go to step 10). If test light does not illuminate, go to next step.
5. Reconnect Blue VCM harness connector. Install Gray jumper wires from Connector Test Kit (J 35616-A) between engine harness connector and crankshaft position sensor. Set DVOM to duty cycle position. Connect DVOM between signal circuit and ground circuit of crankshaft position sensor connector (engine harness side). Crank engine. If duty cycle is less than 30 percent, go to step 11). If duty cycle is not less than specified, go to next step.
6. Check for poor connection at crankshaft position sensor. If connection is faulty, go to step 12).
7. Check for open in ground circuit. If circuit is open, go to step 12). If a circuit is okay, go to step 9).
8. Check for open or short to ground in ignition feed circuit. If a problem was found, go to step 12).
9. Check for poor connection at VCM. If connection is faulty, go to step 12). If connection is okay, go to step 13).
10. Repair short to ground in signal circuit. After repairs, go to step 14).
11. Replace crankshaft position sensor. After replacing sensor, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0337. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC is intermittent, see the TESTS W/O CODES article.

DTC P0338 - CRANKSHAFT POSITION SENSOR CIRCUIT HIGH FREQUENCY

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft Position (CKP) sensor sends a reference signal to VCM indicating crankshaft position and RPM. Information is used to determine when to pulse ignition coil, fuel injectors and control ignition timing.

1. Engine speed is less than 4000 RPM.
2. MAF sensor is at least 5 gm/s.
3. Crank sensor duty cycle is greater than 50 percent (or the ratio high ref/low ref is greater than 5.66).

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if engine starts. If engine starts, go to step 4). If engine does not start, go to next step.
3. Clear DTCs and crank engine for 10 seconds. Check if DTC P0338 sets. If DTC P0338 sets, go to next step. If DTC P0338 does not set, see the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
4. Install scan tool. Start engine and observe engine RPM on scan tool. If RPM fluctuates up to twice the expected RPM, go to step 14). If RPM does not fluctuate up to twice the expected RPM, go to next step.
5. Disconnect crankshaft position sensor connector. Turn ignition on, with engine off. Using test light, probe signal circuit of crankshaft position sensor connector (engine harness side) to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
6. Connect test light between ground circuit and signal circuit of crankshaft position sensor connector (engine harness side). If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
7. Turn ignition off. Install Gray jumper wires from Connector Test Kit(J 35616-A) between engine harness connector and crankshaft position sensor. Start engine. Using DVOM, check voltage on signal circuit. Voltage should be 1-2 volts. If voltage is as specified, go to step 16). If voltage is not as specified, go to step 9).
8. Turn ignition off. Disconnect Blue VCM connector. Using test light, probe signal circuit of crankshaft position sensor connector (engine harness side) to battery voltage. If test light illuminates, go to step 11). If test light does not illuminate, go to step 15).
9. Check for open in signal circuit. If a problem was found, go to step 17). If a problem was not found, go to next step.
10. Check for short to ground in signal circuit. If a problem was found, go to step 17). If a problem was not found, go to step 13).
11. Repair short to ground in ignition feed circuit. After repairs, go to step 19).
12. Repair open in ground circuit. After repairs, go to step 19).
13. Check for poor connection at crankshaft position sensor. If a problem was found, go to step 17). If a problem was not found, go to next step.
14. Replace crankshaft position sensor. After replacing sensor, go to step 19).
15. Check for open in ignition feed circuit. If a problem was found, go to step 17). If a problem was not found, go to next step.
16. Check for poor connection at VCM. If a problem was found, go to next step. If a problem was not found, go to step 18).
17. Repair circuit as necessary. After repairs, go to step 19).
18. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to step 19).
19. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0338. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
20. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC is intermittent, see the TESTS W/O CODES article.

DTC P0339 - CRANKSHAFT POSITION SENSOR CIRCUIT INTERMITTENT

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Crankshaft Position (CKP) sensor sends a reference signal to VCM indicating crankshaft position and RPM. Information is used to determine when to pulse ignition coil, fuel injectors and control ignition timing.

1. MAF sensor is at least 5 gm/s.
2. Change in calculated engine speed is at least 1000 RPM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if engine starts and continues to run. If engine starts and continues to run, see DIAGNOSTIC AIDS. If engine does not start and continues to run, go to next step.
3. Turn ignition off. Disconnect crankshaft position sensor connector. Turn ignition on, with engine off. Using test light, probe ignition feed circuit of crankshaft position sensor connector (engine harness side) to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 6).
4. Install test light between CKP sensor connector (engine harness side) ignition feed circuit and ground circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
5. Turn ignition off. Install Gray jumper wires from Connector Test Kit (J 35616-A) between engine harness connector and crankshaft position sensor. Set DVOM to duty cycle position. Connect DVOM between signal circuit and ground circuit of crankshaft position sensor connector (engine harness side). Crank engine. Duty cycle should be 20-40 percent. If duty cycle is as specified, go to step 8). If duty cycle is not as specified, go to step 10).
6. Repair open or short to ground in ignition feed circuit. After repairs, go to step 13).
7. Check for open in ground circuit. If circuit is open, go to step 11). If circuit is open, go to step 9).
8. With DVOM still connected, set DVOM to AC volt scale. Crank engine. If voltage is greater than 10 volts, go to step 11). If voltage is less than 10 volts, go to next step.
9. Check for open in signal circuit or ground circuit. If a problem was found, go to step 11). If a problem was not found, go to step 12).
10. Replace crankshaft position sensor. Inspect sensor mounting surface and clean debris as necessary. After replacing sensor, go to step 13).
11. Repair as necessary. After repairs, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0339. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Inspect face of crankshaft position sensor for metal shavings. Metal shavings could cause DTC P0339 to set. If DTC is intermittent, see the TESTS W/O CODES article.

DTC P0340 - CAMSHAFT POSITION SENSOR CIRCUIT

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Camshaft Position (CMP) sensor is used to indicate camshaft position so that VCM can determine which cylinder is misfiring when misfire is present. Sensor also checks if high voltage switch is properly installed.

1. Engine running and camshaft position sensor reference pulse is not seen once every 2 revolutions of crankshaft.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. With engine idling, record FREEZE FRAME and FAILURE RECORDS for DTC. Wait one minute with engine idling. Observe LAST TEST FAILED for DTC recorded in FREEZE FRAME. If failed, turn engine off and restart. Check if Malfunction Indicator Light (MIL) is illuminated. If MIL is illuminated, go to next step. If MIL is not illuminated, go to step 8).
3. Turn ignition off. Disconnect camshaft position sensor connector. Turn ignition on, with engine off. Using test light, probe ignition feed circuit of camshaft position sensor connector (engine harness side) to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
4. Connect test light between ground circuit and ignition feed circuit of camshaft position sensor connector (engine harness side). If test light illuminates, go to next step. If test light does not illuminate, go to step 11).
5. Turn ignition off. Install Gray jumper wires from Connector Test Kit(J 35616-A) between engine harness connector and camshaft position sensor. Start engine. Using DVOM, check voltage on signal circuit. If voltage is 5-7 volts, go to step 15). If voltage is not 5-7 volts, go to next step.
6. Check for open in signal circuit. If a problem was found, go to step 13). If a problem was not found, go to next step.
7. Check for short to ground in signal circuit. If a problem was found, go to step 13). If a problem was not found, go to step 12).
8. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
9. Check for open in ignition feed circuit. If a problem was found, go to step 13). If a problem was not found, go to next step.
10. Repair short to ground in ignition feed circuit. After repairs, go to step 17).
11. Repair open in ground circuit. After repairs, go to step 17).
12. Check for poor connection at camshaft position sensor. If a problem was found, go to next step. If a problem was not found, go to step 14).
13. Repair circuit as necessary. After repairs, go to step 17).
14. Replace camshaft position sensor. After replacing sensor, go to step 17).
15. Check for poor connection at VCM. If a problem was found, go to step 13). If a problem was not found, go to next step.
16. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
17. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0340. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
18. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC is intermittent, see the TESTS W/O CODES article.

DTC P0341 - CAMSHAFT POSITION SENSOR CMP) CIRCUIT PERFORMANCE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

If cam/crank sensor pulse ratio is skewed, DTC will set. Fault is not a solid or consistent failure and may not act the same way twice.

1. With engine running, CMP sensor reference pulse is not detected at correct interval.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check for intermittent short to voltage or electromagnetic interference (i.e., wires running along side spark plug wires, high power transmitters such as mobile radios) in camshaft position sensor wires. If a problem was found, go to next step. If a problem was not found, go to step 4).
3. Repair short to voltage or electromagnetic interference as necessary. After repairs, go to next step.
4. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0341. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
5. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. If DTC is intermittent, see the TESTS W/O CODES article.

DTC P0401 - EGR SYSTEM PERFORMANCE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM tests exhaust gas recirculation valve by momentarily commanding valve on while monitoring manifold absolute pressure. If expected manifold absolute pressure increase is not seen under certain operating conditions (decel) for a calibrated number of tests, VCM will turn on Malfunction Indicator Light (MIL) and store DTC P0401.

VCM will run EGR tests when following conditions are present

1. No TP sensor DTCs are set.
2. No MAP sensor DTCs are set.
3. No VSS DTCs are set.
4. No IAT sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No IAC DTCs are set.
7. No linear EGR pintle position DTCs are set.
8. No transmission DTCs are set.
9. No HVAC DTCs are set.
10. Engine coolant temperature is greater than 172°F (78°C).
11. Baro is greater than 70 kPa (less than 10,3000 ft.).
12. Vehicle speed is greater than 30 MPH.
13. AC clutch status is unchanged.
14. Transmission is in locked or unlocked stage (stable).
15. No misfire DTCs are set.
16. Engine speed is 1000-1600 RPM.

1. EGR flow test will fail and DTC P0401 set if VCM does not detect a sufficient rise in manifold absolute pressure during listed conditions.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Using scan tool, select MISCELLANEOUS TESTS, EGR CONTROL and cycle EGR valve through 25, 50, 75 and 100 percent positions. Increase engine speed to greater than 1500 RPM. RPM should drop and engine should run rough as EGR valve is cycled. If engine runs rough as EGR valve is cycled, go to step 5). If engine does not run rough as EGR valve is cycled, go to next step.
3. Turn ignition off. Disconnect EGR valve connector. Turn ignition on, with engine off. Connect test light between EGR control circuit and ignition feed circuit of EGR valve connector (engine harness side). If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
4. Start engine. Using scan tool, select MISCELLANEOUS TESTS, EGR CONTROL and cycle EGR valve. With test light still connected, observe test light as EGR valve is cycled through 100 percent. If test light illuminates, go to step 8). If test light does not illuminate, go to step 11).
5. Remove EGR valve and inspect for restrictions. Inspect if valve pintle is sticking partially open. If a problem was found, go to step 10). If a problem was not found, go to next step.
6. See DIAGNOSTICS AIDS.
7. Check for short to ground in EGR control circuit. If a problem was found, go to step 14). If a problem was not found, go to step 15).
8. Check for a restriction in EGR tube or passage. If a problem was found, go to step 10). If a problem was not found, go to next step.
9. Check for poor connection at EGR valve. If a problem was found, go to step 14). If a problem was not found, go to next step.
10. Replace EGR valve. After replacing EGR valve, go to step 16).
11. Check for open in EGR control circuit. If a problem was found, go to step 14). If a problem was not found, go to next step.
12. Check for open in ignition feed circuit. If a problem was found, go to step 14). If a problem was not found, go to next step.
13. Check for poor connection at VCM. If a problem was found, go to next step. If a problem was not found, go to step 15).
14. Repair circuit as necessary. After repairs, go to step 16).
15. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
16. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0401. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Inspect VCM connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connection. Inspect wiring harness for damage. If connections and harness are okay, observe scan tool while wiggling related connectors and wiring harness. A change in display will indicate location of fault.

If EGR valve indicates signs of excessive heat, check exhaust system for blockage (i.e., plugged converter). If exhaust system is restricted, check for possible open injector cause by grounded driver circuit, injector stuck open or faulty VCM. If problem is not found, check oil for possible fuel contamination.

DTC P0420 - TWC SYSTEM LOW EFFICIENCY BANK 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Three-Way Catalytic Converter (TWC) controls emissions of hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). Catalyst within converter promotes a chemical reaction which oxidizes HC and CO present in exhaust gas, converting them into water vapor and carbon dioxide. Catalyst reduces NOx, converting it to nitrogen. VCM monitors this process using HO2S located in exhaust stream after catalyst.

HO2S produces a signal indicating oxygen storage capacity of catalyst and indicates catalyst's ability to convert exhaust emissions effectively. If catalyst is properly functioning, HO2S signal will be less active than other HO2S located further upstream from catalyst. DTC P0420 will set is HO2S signal is outside of acceptable range for an extended period of time, indicating 3-way catalytic converter oxygen storage capacity is below acceptable threshold. DTC will set when the following conditions are present

Converter Warm-Up Test

1. Vehicle is in "closed loop" fuel control.
2. Commanded air/fuel ratio equals 14.7:1.
3. MAP sensor pressure is greater than 15 gm/s.
4. Predicted catalyst warm up temperature is greater than 842°F (450°C).

Converter Warm-Up Test Passed

1. No VSS DTCs are set.
2. No TP sensor DTCs are set.
3. No HO2S DTCs are set.
4. No misfire DTCs are set.
5. No MAP sensor DTCs are set.
6. No fuel trim DTCs are set.
7. No IAT sensor DTCs are set.
8. No ECT sensor DTCs are set.
9. No MAF sensor DTCs are set.
10. Engine coolant temperature greater than 167°F (75°C).
11. Vehicle is in "closed loop" fuel control.
12. Listed conditions are met for a period of time to ensure a warm catalyst (at least 2 consecutive minutes).
13. Calculated engine load is steady.
14. Vehicle speed is steady between 20-70 MPH.
15. Intake air temperature is at least 14.5°F (-9.75°C).
16. MAF sensor is less than 50 gm/s.
17. Engine speed is not greater than 4900 RPM.
18. TP sensor is greater than 1.9 percent.
19. Pre-catalyst HO2S average is within 8 millivolts of catalyst monitored HO2S average voltage.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any MAP sensor, HO2S, misfire, fuel trim, VSS or ECT sensor DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Check for the following conditions: Ensure TWC system is original equipment installed by manufacturer. Check TWC system for damage (i.e., dents, severe discoloration caused by excessive temperatures, holes). Ensure internal converter rattle (caused by damaged catalyst) is not present. Check exhaust system between TWC system and rear converter flange for leaks, damage, or loose or missing hardware. Ensure HO2S bank 1, sensor 2 is secure, and pigtail and wiring is not damaged or contacting exhaust. If a problem was found, go to step 9). If a problem was not found, go to next step.
4. Check all VCM grounds. If a problem was found, go to step 9). If a problem was not found, go to next step.
5. Check all sensor grounds. If a problem was found, go to step 9). If a problem was not found, go to next step.
6. Check for intermittent open in catalyst monitored HO2S signal and ground circuits. If a problem was found, go to step 9). If a problem was not found, go to next step.
7. Check for intermittent short to ground on catalyst monitored HO2S signal and ground circuits. If a problem was found, go to step 9). If a problem was not found, go to next step.
8. Replace TWC system. Check for possible misfire (DTC P0300) or engine mechanical problem. Go to step 10).
9. Repair problem as necessary. After repairs, go to next step.
10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0420. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Difficulty running OBD-II status DTC P0420 test may be encountered in areas where test conditions cannot be easily maintained, especially in urban areas.

DTC P0430 - TWC SYSTEM LOW EFFICIENCY BANK 2

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Three-Way Catalytic (TWC) converter controls emissions of hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). Catalyst within converter promotes a chemical reaction which oxidizes HC and CO present in exhaust gas, converting them into water vapor and carbon dioxide. Catalyst reduces NOx, converting it to nitrogen. VCM monitors this process using HO2S located in exhaust stream after catalyst.

HO2S produces a signal indicating oxygen storage capacity of catalyst and indicates catalyst's ability to convert exhaust emissions effectively. If catalyst is properly functioning, HO2S signal will be less active than other HO2S located further upstream from catalyst. DTC P0430 will set is HO2S signal is outside of acceptable range for an extended period of time, indicating 3-way catalytic converter oxygen storage capacity is below acceptable threshold.

1. No VSS DTCs are set.
2. No TP sensor DTCs are set.
3. No HO2S DTCs are set.
4. No misfire DTCs are set.
5. No MAP sensor DTCs are set.
6. No fuel trim DTCs are set.
7. No ECT sensor DTCs are set.
8. Engine coolant temperature is greater than 185°F (85°C).
9. Vehicle is in "closed loop" fuel control.
10. Listed conditions are met for a period of time to ensure a warm catalyst (at least 2 consecutive minutes).
11. Calculated engine load is steady.
12. Vehicle speed is steady between 20-70 MPH.
13. Catalyst monitored HO2S signal activity has been determined to be excessive by VCM.
14. Listed conditions are met for up to 2 additional minutes after catalyst warm-up criteria has been met.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any MAP sensor, HO2S, misfire, fuel trim, VSS or ECT sensor DTCs are set. If any other DTCs are set, go to step 4). If no other DTCs are set, go to next step.
3. Check for the following conditions: Ensure TWC system is original equipment installed by manufacturer. Check TWC system for damage (i.e., dents, severe discoloration caused by excessive temperatures, holes). Ensure internal converter rattle (caused by damaged catalyst) is not present. Check exhaust system between TWC system and rear converter flange for leaks, damage, or loose or missing hardware. Ensure HO2S bank 2, sensor 2 is secure, and pigtail and wiring is not damaged or contacting exhaust. If a problem was found, go to step 10). If a problem was not found, go to step 5).
4. Go to applicable DTC test.
5. Check all VCM grounds. If a problem was found, go to step 10). If a problem was not found, go to next step.
6. Check all sensor grounds. If a problem was found, go to step 10). If a problem was not found, go to next step.
7. Check for intermittent open in catalyst monitored HO2S signal and ground circuits. If a problem was found, go to step 10). If a problem was not found, go to next step.
8. Check for intermittent short to ground on catalyst monitored HO2S signal and ground circuits. If a problem was found, go to step 10). If a problem was not found, go to next step.
9. Replace TWC system. Check for possible misfire (DTC P0300) or engine mechanical problem. After replacing converter, go to step 11).
10. Repair problem as necessary. After repairs, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0430. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Difficulty running OBD-II status DTC P0430 test may be encountered in areas where test conditions cannot be easily maintained, especially in urban areas. To minimize driving time required to complete test, catalyst can be warmed up in service bay previous to drive cycle. Engine can also be warmed up in service bay.

Using scan tool, monitor MAP sensor; HO2S bank 2, sensor 1 and HO2S bank 2, sensor 2 displays with gear selector in Park or Neutral with engine above idle. Compare HO2S activity (amplitude and frequency) to each other during a 30 second time period. If HO2S 2 activity is nearly as great as HO2S 1 activity, a problem is present. If less activity is indicated, TWC system is properly functioning.

DTC P0441 - EVAP SYSTEM NO FLOW DURING PURGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Canister purge is controlled by a solenoid valve that allows ported vacuum to purge canister when energized. VCM supplies ground to energize solenoid valve which is pulse width modulated. Duty cycle is determined by closed loop feedback from HO2S. Duty cycle is calculated by VCM and output is commanded when certain conditions have been met.

A vacuum switch in purge line is used to detect when system is being purged. Normally closed switch will open when less than one in. Hg is present in purge line. VCM supplies a 12-volt reference to switch to monitor if evaporative emission control system is operating properly. DTC will set if switch is closed when VCM is commanding purge.

DTC will set when the following conditions are present

1. Purge solenoid diagnostic vacuum switch DTC is not set.
2. No IAC DTCs are set.
3. No MAP sensor DTCs are set.
4. No TP sensor DTCs are set.
5. No EGR DTCs are set.
6. BARO is greater than 75 kPa.
7. Engine coolant temperature is less than 230°F (110°C).
8. Power-up intake air temperature is greater than -.4°F (-18°C).
9. Intake air temperature is less than or equal to 194°F (90°C).
10. Change in engine coolant temperature/intake air temperature is less than or equal to 194°F (90°C).
11. Purge DC is greater than or equal to 90 percent.
12. MAP is greater than or equal to 20 kPa, but less than or equal to 80 kPa.
13. Throttle position is greater than or equal to 5 percent, but less than or equal to 60 percent.
14. Engine speed is greater than or equal to 800 RPM, but less than or equal to 3000 RPM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, command EVAP solenoid valve on and off while listening to solenoid valve. If solenoid valve turns on and off when commanded, go to next step. If solenoid valve does not turn on and off when commanded, go to step 5).
3. Disconnect throttle body to EVAP solenoid valve vacuum hose. Install vacuum gauge to disconnected hose. Start engine. Allow engine RPM to stabilize at 2500 RPM. Momentarily snap throttle open and allow to return to idle. If 10 in. Hg vacuum is present at EVAP solenoid valve, go to next step. If 10 in. Hg vacuum is not present, go to step 7).
4. Turn ignition off. Disconnect EVAP vacuum switch connector. Turn ignition on, with engine off. If scan tool indicates EVAP vacuum switch on, go to step 8). If scan tool does not indicate EVAP vacuum switch on, go to step 12).
5. Turn ignition off. Disconnect EVAP solenoid valve connector. Turn ignition on, with engine off. Using test light, probe control circuit of EVAP solenoid valve connector to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
6. Connect test light between EVAP connector terminals (engine harness side). Using scan tool, command EVAP solenoid valve on and off. If test light flashes on and off, go to step 10). If test light does not flash on and off, go to step 11).
7. See DIAGNOSTIC AIDS.
8. Check for pinched, kinked of clogged hoses to EVAP vacuum switch. If a problem was found, go to step 14). If a problem was not found, go to step 13).
9. Repair open in EVAP solenoid valve ignition feed circuit. After repairs, go to step 16).
10. Replace EVAP solenoid valve. After replacing EVAP solenoid, go to step 16).
11. Check for open or short to voltage in EVAP solenoid valve control circuit. If a problem was found, go to step 14). If a problem was not found, go to step 15).
12. Check for short to ground in EVAP vacuum switch signal circuit. If circuit is shorted, go to step 14). If circuit is okay, go to step 15).
13. Replace EVAP vacuum switch. After replacing vacuum switch, go to step 16).
14. Repair as necessary. After repairs, go to step 16).
15. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
16. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0441. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Visually inspect vacuum hoses. Check throttle body for possible cracked, broken or plugged vacuum block. Check engine for possible mechanical problem.

DTC P0500 - VEHICLE SPEED SENSOR CIRCUIT

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Vehicle Speed Sensor (VSS) circuit is a magnetic induction type sensor. Gear teeth pressed on outside diameter of output shaft assembly induce an alternating current in sensor as shaft rotates. Signal goes directly to VCM. Pulsing action takes place about 40 times per revolution of output shaft of transmission and VCM will calculate vehicle speed based on time between pulses.

1. No MAP sensor DTCs are set.
2. Vehicle speed less than one MPH.
3. Throttle angle less than 3 percent.
4. Engine coolant temperature greater than 140°F (60°C).
5. Engine speed is 1400-4400 RPM.
6. MAP pressure is less than 20 kPa.
7. All conditions are met for 5 seconds.
8. No MAP sensor DTCs are set.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Clear DTCs. Using Connector Test Kit (J 35616-A), backprobe signal and ground circuits of VSS connector. Raise vehicle wheels and place engine in operating gear. Check voltage with voltmeter on 200-volt AC scale. If voltage is constant, go to step 5). If voltage is not constant, go to next step.
3. If voltage varies, see DIAGNOSTIC AIDS. If voltage does not vary, go to next step.
4. If voltmeter indicates no voltage, go to step 11). If voltmeter does not indicate no voltage, go to step 12).
5. Turn ignition off. Disconnect VSS connector. With vehicle still raised, engine operating, transmission in gear and voltmeter on 200-volt AC scale, check voltage between VSS connector terminals. If voltage varies with RPM, go to step 7). If voltage does not vary with RPM, go to next step.
6. Replace VSS. Go to step 12).
7. Check for poor connections at VCM and VSS. If a problem was found, go to step 9). If a problem was not found, go to next step.
8. Check for open or short in VSS signal and ground circuits. If a problem was found, go to step 10). If a problem was not found, go to step 12).
9. Repair connections as necessary. After repairs, go to step 12).
10. Repair open or short as necessary. After repairs, go to step 12).
11. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0500. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check for proper calibration of speedometer.

DTC P0506 - IDLE SYSTEM LOW RPM (IAC RESPONDING)

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM controls idle speed with an Idle Air Control (IAC) valve to a calculated desired RPM based on sensor inputs and actual engine RPM. VCM uses 4 circuits to move an IAC valve, allowing varying amounts of airflow into intake manifold.

To increase idle RPM, VCM moves IAC valve out, allowing more air to by-pass throttle plate. To decrease RPM, VCM moves IAC valve in, reducing amount of air by-passing throttle plate. Scan tool reads VCM commands to IAC valve in counts. The higher the counts, the more air that is allowed to by-pass throttle plate (higher idle). The lower the counts, less air is allowed to by-pass throttle plates (lower idle).

1. No TP sensor DTCs are set.
2. No ECT sensor DTCs are set.
3. ECT greater than 162°F (72°C).
4. IAT greater than -13°F (-25°C).
5. BARO is greater than 70 kPa (less than 10,300 ft.).
6. Vehicle speed is less than 2 MPH.
7. No VSS DTCs are set.
8. No MAP sensor DTCs are set.
9. System voltage greater than 10 volts but less than 18 volts.
10. Engine run time is greater than 30 seconds.
11. Throttle position is less than 1 percent.
12. All conditions are met for greater than 3 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Check if any other DTCs are set. If other DTCs are not set, go to next step. If other DTCs are set, go to that DTC test.
3. Check if DTC P0506 is active this ignition cycle. If DTC P0506 is active this ignition cycle, go to step 5). If DTC P0506 is not active this ignition cycle, go to next step.
4. DTC is intermittent. See DIAGNOSTIC AIDS.
5. Problem is engine mechanical related. Repair as necessary. After repairs, go to step 7).
6. Using scan tool, clear codes. Start engine. Idle at operating temperature. Select SPECIFIC DTC for DTC P0506. Operate vehicle under conditions which originally set DTC. If scan tool indicates DTC test has run and passed, go to next step. if not, go to step 2).
7. Using scan tool, select CAPTURE INFO function. Review stored info. If other DTCs are stored, go to applicable DTC. If not, system is okay.

DTC could be caused by an IAC valve which is stopped and cannot respond to VCM, a throttle stop screw which has been tampered with, or a damaged throttle or linkage.

A slow, unstable or fast idle could be caused by a non-IAC valve system problem that cannot be overcome by IAC valve. See the TESTS W/O CODES article. Out of range control IAC scan tool counts will be greater than 60 if idle is too low and zero if idle is too high. Check for fuel system too lean and rich. Check throttle body bore for foreign material. IAC reset is done with scan tool miscellaneous functions mode.

DTC P0507 - IDLE SYSTEM HIGH IDLE AIR CONTROL RESPONDING

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM controls idle speed with an Idle Air Control (IAC) valve to a calculated desired RPM based on sensor inputs and actual engine RPM. VCM uses 4 circuits to move an IAC valve, allowing varying amounts of airflow into intake manifold.

To increase idle RPM, VCM moves IAC valve out, allowing more air to by-pass throttle plate. To decrease RPM, VCM moves IAC valve in, reducing amount of air by-passing throttle plate. Scan tool reads VCM commands to IAC valve in counts. The higher the counts, the more air that is allowed to by-pass throttle plate (higher idle). The lower the counts, less air is allowed to by-pass throttle plates (lower idle).

1. No TP sensor DTCs are set.
2. No ECT sensor DTCs are set.
3. Engine coolant temperature is greater than 162°F (72°C).
4. Intake air temperature is greater than -13°F (-25°C).
5. BARO is greater than 70 kPa (less than 10,300 ft.).
6. VSS is less than 2 MPH.
7. No VSS DTCs are set.
8. No MAP sensor DTCs are set.
9. System voltage is greater than 10 volts but less than 18 volts.
10. Engine run time is greater than 30 seconds.
11. Throttle position is less than one percent.
12. All conditions are met for greater than 3 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Check if any other DTCs are set. If other DTCs are not set, go to next step. If other DTCs are set, go to that DTC test.
3. Check if DTC P0507 is active this ignition cycle. If DTC P0507 is active this ignition cycle, go to step 5). If DTC P0507 is not active this ignition cycle, go to next step.
4. DTC is intermittent. See DIAGNOSTIC AIDS.
5. Problem is engine mechanical related. Repair as necessary and go to step 7).
6. Using scan tool, clear codes. Start engine. Idle at operating temperature. Select SPECIFIC DTC for DTC P0507. Operate vehicle under conditions which originally set DTC. If scan tool indicates DTC test has run and passed, go to next step. if not, go to step 2).
7. Using scan tool, select CAPTURE INFO function. Review stored info. If other DTCs are stored, go to applicable DTC. If not, system is okay.

DTC could be caused by an IAC valve which is stopped and cannot respond to VCM, a throttle stop screw which has been tampered with, or a damaged throttle or linkage.

A slow, unstable or fast idle could be caused by a non-IAC valve system problem that cannot be overcome by IAC valve. See the TESTS W/O CODES article. Out of range control IAC scan tool counts will be greater than 60 if idle is too low, and zero if idle is too high. Check for fuel system too lean and rich. Check throttle body bore for foreign material. IAC reset is done with scan tool miscellaneous functions mode.

DTC P1106 - MAP SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). A 5-volt reference is applied to sensor. A variable resistor moves in relation to manifold pressure and a voltage signal is returned to VCM through MAP signal circuit. Voltage signal varies from 1.0-1.5 volts at closed throttle to 4.0-4.5 volts at wide open throttle (low vacuum). VCM utilizes MAP signal and throttle position to determine fuel delivery.

1. MAP pressure is greater than or equal to 5 volts.
2. No TP sensor DTCs are set.
3. Throttle position is not greater than 96.8 percent when engine speed is not greater than 1000 RPM or throttle position is not greater than 89.8 percent when engine speed is greater than 1000 RPM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. If engine idle is unstable, incorrect, or if manifold vacuum at idle is less than 15 in. Hg, repair as necessary. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to next step. If MAP sensor voltage is less than 4 volts, go to step 4).
3. Turn ignition off. Disconnect MAP sensor connector. Turn ignition on. Monitor MAP sensor voltage using scan tool. If MAP sensor voltage is less than one volt, go to step 5). If MAP sensor voltage is not less than one volt, go to step 9).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. With DVOM to ground, probe 5-volt reference circuit at MAP sensor connector. If voltage is greater than 5.2 volts, go to step 10). If not, go to next step.
6. Using test light, probe MAP sensor connector ground circuit to battery voltage. If test light illuminates, go to step 7). If test light does not illuminate, go to step 14).
7. Check for restriction in MAP sensor vacuum source. If a problem was found, go to step 15). If a problem was not found, go to next step.
8. Replace MAP sensor. After replacing sensor, go to step 19).
9. Check for short to voltage in MAP signal circuit. If a problem was found, go to step 15). If a problem was not found, go to step 18).
10. Ignition off. Unplug VCM Gray connector. Ignition on. With DVOM to ground, check voltage on VCM connector MAP sensor 5-volt reference circuit terminal. If voltage is greater than 5.2 volts, go to next step. If not, go to step 13).
11. Unplug EGR electrical connector. Check voltage on VCM connector EGR sensor 5-volt reference circuit terminal. If voltage is greater than 5.2 volts, go to next step. If not, go to step 16).
12. Repair short to voltage on 5-volt reference circuit. After repairs, go to step 19).
13. With DVOM to ground, measure voltage on VCM connector TP sensor 5-volt reference circuit terminal. If voltage is greater than 5.2 volts, go to step 17). If not, go to step 18).
14. Repair MAP ground circuit. After repairs, go to step 19).
15. Repair as necessary. After repairs, go to step 19).
16. Replace EGR valve. After replacing EGR valve, go to step 19).
17. Repair short to voltage on the 5-volt reference circuit. After repairs, go to step 19).
18. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
19. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1106. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
20. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent ground in MAP signal circuit or 5-volt reference circuit will result in DTC P1106 setting. With ignition on and engine off, manifold pressure is equal to atmospheric pressure with signal voltage high. VCM uses information as an indication of vehicle altitude.

To test accuracy of a suspect sensor, compare reading with a known-good vehicle. Reading should be 3.6-4.9 volts. If DTC is intermittent, see the TESTS W/O CODES article. To check for intermittent connection, disconnect sensor from bracket and twist sensor by hand. Output changes greater than .1 volt indicates a poor connection or connector. If okay, replace sensor. Ensure electrical connection remains securely connected. If sensor is removed from intake manifold, sensor-to-manifold seal must be replaced.

DTC P1107 - MAP SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). A 5-volt reference is applied to sensor. A variable resistor moves in relation to manifold pressure and a voltage signal is returned to VCM through MAP signal circuit. Voltage signal varies from 1.0-1.5 volts at closed throttle to 4.0-4.5 volts at wide open throttle (low vacuum). VCM utilizes MAP signal and throttle position to determine fuel delivery.

1. No TP sensor DTCs are set.
2. Engine is running.
3. Throttle position is at least zero percent when engine speed is not greater than 1000 RPM or throttle position is at least 12.5 percent when engine speed is greater than 1000 RPM.
4. MAP sensor voltage is less than .25 volt.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is less than .5 volt, go to next step. If MAP sensor voltage is greater than .5 volt, go to step 5).
3. Turn ignition off. Disconnect MAP sensor connector. Connect a jumper wire between 5-volt reference circuit and signal circuit of MAP sensor connector. Turn ignition on. Monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4.7 volts, go to step 6). If MAP sensor voltage is not greater than 4.7 volts, go to next step.
4. Turn ignition off. Remove jumper wire. Using test light, probe MAP sensor connector signal circuit to battery voltage. Turn ignition on. Monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4.7 volts, go to step 9). If MAP sensor voltage is not greater than 4.7 volts, go to step 7).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for poor connection at MAP sensor. If a problem is found, go to step 12). If a problem is not found, go to step 11).
7. Check for open in MAP signal circuit. If a problem is found, go to step 12). If a problem is not found, go to next step.
8. Check for short to ground in MAP signal circuit. If a problem is found, go to step 12). If a problem is not found, go to step 13).
9. Check for open in MAP 5-volt reference circuit. If a problem is found, go to step 12). If a problem is not found, go to next step.
10. Check for short to ground in MAP 5-volt reference circuit. If a problem is found, go to step 12). If a problem is not found, go to step 13).
11. Replace MAP sensor. After replacing sensor, go to step 14).
12. Repair circuit as necessary. After replacing sensor, go to step 14).
13. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1107. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent open in MAP signal circuit or 5-volt reference circuit will result in DTC P1107 setting. With ignition on and engine off, manifold pressure is equal to atmospheric pressure with signal voltage high. VCM uses information as an indication of vehicle altitude.

To test accuracy of a suspect sensor, compare reading with a known-good vehicle. Reading should be 3.6-4.9 volts. If DTC is intermittent, see the TESTS W/O CODES article. To check for intermittent connection, disconnect sensor from bracket and twist sensor by hand. Output changes greater than .1 volt indicates a poor connection or connector. If okay, replace sensor. Ensure electrical connection remains securely connected. If sensor is removed from intake manifold, sensor-to-manifold seal must be replaced.

DTC P1111 - IAT SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Intake Air Temperature (IAT) sensor is a thermistor located in fresh air duct to throttle body. It is used to monitor temperature of air entering throttle body. VCM supplies 5 volts to sensor. When air is cool, sensor resistance will be high and VCM will sense a high voltage signal. When air is warm, sensor resistance will be low and VCM will sense a low voltage signal.

1. No ECT DTCs set.
2. No VSS DTCs set.
3. No MAF DTCs set.
4. Vehicle speed is less than 2 MPH.
5. MAF less than 250 gm/s.
6. Engine coolant temperature is greater than 183°F (84°C).
7. Engine run time greater than 100 seconds.
8. Intake air temperature greater than 4.9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Monitor IAT sensor voltage on scan tool. If voltage is greater than 4.9 volts, go to next step. If voltage is not greater than 4.9 volts, go to step 6).
3. Turn engine off. Disconnect IAT sensor connector. Turn ignition on. Connect a jumper wire between IAT sensor terminals. Monitor IAT sensor voltage on scan tool. If voltage is less than .82 volt, go to step 7). If voltage is not less than .82 volt, go to next step.
4. Connect a jumper wire between IAT signal circuit of IAT sensor connector and ground. Monitor IAT sensor voltage on scan tool. If voltage is less than .82 volt, go to step 8). If voltage is not less than .82 volt, go to next step.
5. Check if DTC P0123 is also set. If DTC P0123 is set, go to «DTC P0123»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0123-tp-sensor-circuit) . If DTC P0123 is not set, go to step 9).
6. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
7. Check for poor connections at IAT sensor and VCM. If a problem was found, go to step 10). If a problem is not found, go to step 12).
8. Check for open in IAT ground circuit between IAT sensor and VCM. If IAT signal circuit is open, go to step 10). If IAT signal circuit is not open, go to step 12).
9. Check for open in IAT signal circuit between IAT sensor and VCM. If IAT signal circuit is open, go to step 10). If IAT signal circuit is not open, go to step 12).
10. Repair as necessary. After repairs, go to step 13).
11. Replace IAT sensor. After replacing sensor, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1111. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool indicates temperature of ambient air entering throttle body. Air temperature should be very close to temperature of outside air and should gradually rise as engine warms and underhood temperature increases. If DTC P1111 is set, problem is intermittent. Check for poor connections at IAT sensor and VCM by wiggling wiring harness and monitoring IAT temperature or voltage on scan tool. Check for poor connection at point where scan tool display changed. Also, check for a skewed or mis-scaled sensor. See IAT TEMPERATURE-TO-RESISTANCE VALUES table.

IAT TEMPERATURE-TO-RESISTANCE VALUES

DTC P1112 - IAT SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Intake Air Temperature (IAT) sensor is a thermistor located in fresh air duct to throttle body. It is used to monitor temperature of air entering throttle body. VCM supplies 5 volts to sensor. When air is cool, sensor resistance will be high and VCM will sense a high voltage signal. When air is warm, sensor resistance will be low and VCM will sense a low voltage signal.

1. No VSS DTCs are set.
2. Vehicle speed is at least 2 MPH.
3. Engine run time is greater than 100 seconds.
4. IAT voltage is less than .82 volt.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Monitor IAT sensor voltage on scan tool. If voltage is less than .82 volt, go to next step. If voltage is not less than .82 volt, go to step 5).
3. Turn engine off. Disconnect IAT sensor connector. Turn ignition on. Monitor IAT sensor voltage on scan tool. If voltage is greater than 4 volts, go to step 7). If voltage is not greater than 4 volts, go to next step.
4. Turn ignition off. Using DVOM, check resistance between IAT sensor connector terminals. If resistance is infinite, go to step 8). If resistance is not infinite, go to step 6).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Repair short to ground in IAT signal circuit. After repairs, go to step 9).
7. Replace IAT sensor. After replacing sensor, go to step 9).
8. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1112. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool indicates temperature of ambient air entering throttle body. Air temperature should be very close to temperature of outside air and should gradually rise as engine warms and underhood temperature increases. If DTC P1112 is set, problem is intermittent. Check for short to ground in IAT signal circuit by wiggling wiring harness at various locations and monitoring IAT temperature or voltage on scan tool. Check for short to ground at point where scan tool display changed. Also, check for a skewed or mis-scaled sensor. See IAT TEMPERATURE-TO-RESISTANCE VALUES.

DTC P1114 - ECT SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Engine Coolant Temperature (ECT) sensor is a thermistor located in intake manifold cooling system passage used to monitor engine coolant temperature. VCM supplies 5 volts to sensor. When engine coolant is cool, sensor resistance will be high and VCM will sense a high voltage signal. When engine coolant is warm, sensor resistance will be low and VCM will sense a low voltage signal.

1. Engine is running.
2. ECT voltage is less than .78 volt for 5 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Monitor ECT sensor voltage on scan tool. If voltage is less than .82 volt, go to next step. If voltage is not less than .82 volt, go to step 5).
3. Turn engine off. Disconnect ECT sensor connector. Turn ignition on. Monitor ECT sensor voltage on scan tool. If voltage is greater than 4 volts, go to step 7). If voltage is not greater than 4 volts, go to next step.
4. Turn ignition off. Using DVOM, check resistance between ECT sensor connector terminals. If resistance is infinite, go to step 8). If resistance is not infinite, go to step 6).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Repair short to ground in ECT signal circuit. After repairs, go to step 9).
7. Replace ECT sensor. After replacing sensor, go to step 9).
8. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1114. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool displays engine temperature in degrees centigrade. After engine is started, temperature should steadily rise to about 90C then stabilize when thermostat opens. A poor connection or open in 5-volt reference circuit or ground circuit will cause DTC P0117 to set. A skewed or mis-scaled sensor could cause poor driveability conditions. See ECT TEMPERATURE-TO-RESISTANCE VALUES .

DTC P1115 - ECT SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Engine Coolant Temperature (ECT) sensor is a thermistor located in intake manifold cooling system passage used to monitor engine coolant temperature. VCM supplies 5 volts to sensor. When engine coolant is cool, sensor resistance will be high and VCM will sense a high voltage signal. When engine coolant is warm, sensor resistance will be low and VCM will sense a low voltage signal.

1. Engine is running.
2. ECT voltage is greater than 4.9 volt for 5 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Monitor ECT sensor voltage on scan tool. If voltage is greater than 4.9 volts, go to next step. If voltage is not greater than 4.9 volts, go to step 5).
3. Turn engine off. Disconnect ECT sensor connector. Turn ignition on. Connect a jumper wire between ECT sensor terminals. Monitor ECT sensor voltage on scan tool. If voltage is less than .82 volt, go to step 6). If voltage is not less than .82 volt, go to next step.
4. Connect a jumper wire between ECT signal circuit of ECT sensor connector and ground. Monitor ECT sensor voltage on scan tool. If voltage is less than .82 volt, go to step 7). If voltage is not less than .82 volt, go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for poor connections at ECT sensor and VCM. If a problem was found, go to step 10). If a problem is not found, go to step 11).
7. Check for open in ECT ground circuit between ECT sensor and VCM. If ECT ground circuit is open, go to step 10). If ECT ground circuit is not open, go to step 12).
8. Check if DTC P0123 is also set. If DTC P0123 is set, go to «DTC P0123»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0123-tp-sensor-circuit) . If DTC P0123 is not set, go to next step.
9. Check for open in ECT signal circuit between ECT sensor and VCM. If ECT signal circuit is open, go to next step. If ECT signal circuit is not open, go to step 12).
10. Repair as necessary. After repairs, go to step 13).
11. Replace ECT sensor. After replacing sensor, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1115. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check harness routing for short to ground in 5-volt reference circuit. Scan tool displays engine temperature in degrees centigrade. After engine is started, temperature should steadily rise to about 90C then stabilize when thermostat opens. A skewed or mis-scaled sensor could cause poor driveability conditions. See ECT TEMPERATURE-TO-RESISTANCE VALUES .

DTC P1121 - TP SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle opening. Signal voltage varies from about .5 volt at idle to about 4.5 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by VCM for fuel control and most VCM control outputs.

1. Engine is running.
2. TP sensor voltage is greater than 4.7 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. With throttle closed, monitor TP signal voltage using scan tool. If TP signal voltage is greater than 4.8 volts, go to next step. If TP signal voltage is not greater than 4.8 volts, go to step 6).
3. Disconnect TP sensor connector. Monitor TP signal voltage using scan tool. If TP signal voltage is less than .2 volt, go to next step. If TP signal voltage is not less than .2 volt, go to step 5).
4. Using test light, probe TP sensor connector ground circuit to battery voltage. If test light illuminates, go to step 7). If test light does not illuminate, go to step 9).
5. Check if DTC P0108 is also set. If DTC P0108 is set, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If DTC P0108 is not set, go to step 8).
6. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
7. Check for poor connections at TP sensor. If a problem is found, go to step 10). If a problem is not found, go to step 11).
8. Check for short to voltage in TP signal circuit. If a problem is found, go to step 10). If a problem is not found, go to step 12).
9. Check for open in TP ground circuit. After repairs, go to next step.
10. Repair circuit as necessary. After repairs, go to step 13).
11. Replace TP sensor. After replacing sensor, go to step 13).
12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1121. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool displays throttle position in volts. Voltage should be .45-.85 volt with throttle closed and ignition on or at idle. Voltage should steadily increase as throttle is moved toward WOT. Scan tool throttle angle percentage will display as zero percent being closed throttle and 100 percent being WOT. While depressing accelerator pedal with engine stopped and ignition on, TP signal voltage should vary from less than 1.25 volts with throttle closed to greater than 4.5 volts with WOT. If DTC is intermittent, see the TESTS W/O CODES article.

DTC P1122 - TP SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle opening. Signal voltage varies from about .5 volt at idle to about 4.5 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by VCM for fuel control and most VCM control outputs.

1. Engine is running.
2. TP sensor voltage is less than .25 volt.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. With throttle closed, monitor TP signal voltage using scan tool. If TP signal voltage is less than .15 volt, go to next step. If TP signal voltage is not less than .15 volt, go to step 5).
3. Disconnect TP sensor connector. Connect a jumper wire between TP signal circuit and 5-volt reference circuit of TP sensor connector. Monitor TP signal voltage using scan tool. If TP signal voltage is greater than 4 volts, go to step 12). If TP signal voltage is not greater than 4 volts, go to next step.
4. Using a test light connected to ground, probe TP sensor connector signal circuit. Monitor TP signal voltage using scan tool. If TP signal voltage is greater than 4 volts, go to step 6). If TP signal voltage is not greater than 4 volts, go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for open in 5-volt reference circuit. If a problem is found, go to step 11). If a problem is not found, go to next step.
7. Check for short to ground in 5-volt reference circuit. If a problem is found, go to step 11). If a problem is not found, go to step 10).
8. Check for open in TP signal circuit. If circuit is open, step 11). If circuit is okay, go to next step.
9. Check for short to ground in TP signal circuit. If a problem is found, go to step 11). If a problem is not found, go to next step.
10. Check for poor connections at VCM. If a problem is found, go to step 11). If a problem is not found, go to step 13).
11. Repair circuit as necessary. After repairs, go to step 14).
12. Replace TP sensor. After replacing sensor, go to step 14).
13. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1122. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool displays throttle position in volts. Voltage should be .45-.85 volt with throttle closed and ignition on or at idle. An open or short to ground in 5-volt reference circuit or TP signal circuit will cause DTC P0122 to set. If DTC is intermittent, see the TESTS W/O CODES article. While depressing accelerator pedal with engine stopped and ignition on, TP signal voltage should vary from less than 1.25 volts with throttle closed to greater than 4.5 volts with WOT.

DTC P1133 - HO2S INSUFFICIENT SWITCHING BANK 1, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (360°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S is operating properly by monitoring number of lean/rich and rich/lean switches. DTC will set when the following conditions are present

HO2S Diagnostic Enable

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No EGR DTCs are set.
5. No ECT sensor DTCs are set.
6. No misfire DTCs set.
7. No intrusive test in progress.
8. No device controls active
9. System voltage is greater than or equal to 9 volts.

Response Test Enable

1. Closed-loop low MAP not active.
2. Closed-loop Mode 0 not active.
3. Closed-loop.
4. ECT greater than 135°F (57°C).
5. Engine run time greater than 75 seconds.
6. MAF greater than 15 gm/s but with engine at less than 3000 RPM.
7. Canister purge duty cycle is greater than zero percent.
8. Conditions present for greater than 2 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to step 3).
3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If MAP sensor voltage is not greater than 4 volts, go to next step.
4. Check for the following conditions: Air intake duct for improper installation. Air intake duct for collapsed or restriction, for missing or plugged air filter. Throttle body and intake manifold for vacuum leaks. Throttle body for damage to inlet or for foreign objects partially blocking inlet. Throttle body for coking or objects blocking IAC valve passages. Exhaust system for corrosion, leaks, loose or missing hardware. HO2S is installed securely and pigtail harness is not contacting exhaust manifold or wires. Vacuum hoses for splits, kinks and proper connections. Fuel for excessive water, alcohol or other contaminants. VCM sensor grounds are clean, tight and in proper locations. Fuel pressure regulator. If a problem was found, go to next step. If a problem was not found, go to step 6).
5. Repair or replace as necessary. After repairs, go to step 10).
6. Perform injector coil test. See the SYSTEM/COMPONENT TESTS article. If a problem was found, go to step 9). If a problem was not found, go to next step.
7. Remove HO2S bank, 1 sensor 1 and inspect for contamination. If contamination is present, go to next step. If contamination is not present, see DIAGNOSTIC AIDS.
8. Replace HO2S bank 1, sensor 1. After replacing HO2S sensor, go to step 10).
9. Replace fuel injector. After replacing injector, go to step 10).
10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1133. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check HO2S heater operation.

DTC P1134 - HO2S TRANSITION TIME RATIO BANK 1, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

This diagnostic test is used in conjunction with HO2S bank 1, sensor 1 slow response diagnostic test P0133. Ratio of response times that were calculated are compared to calibrated limits. If number of lean to rich and rich to lean transitions were zero, ratios will be set to zero. Otherwise, ratio is calculated based on which average response time was greater. DTC will set when the following conditions are present

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No EGR DTCs are set.
6. No ECT sensor DTCs are set.
7. No misfire DTCs are set.
8. No intrusive test in progress.
9. No device controls active.
10. System voltage is greater than or equal to 9 volts.

1. Closed-loop low MAP not active.
2. Closed-loop Mode 0 not active.
3. DTCs P0131, P0132, P0134 and P0135 not active.
4. System in "closed-loop".
5. ECT greater than 135°F (57°C).
6. Engine run time greater than 75 seconds.
7. MAF greater than 15 gm/s with engine speed at less than 3000 RPM.
8. Average response time calculations completed for this ignition cycle.
9. Ratio of left HO2S left right/right left times greater than 64 counts.
10. Ratio of left HO2S left right/right left times greater than 48 counts.
11. Canister purge duty cycle is greater than zero percent.
12. Conditions present for greater than 2 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Start engine and idle until normal operating temperature is reached. Observe engine coolant temperature using scan tool while operating engine at a steady speed of 1200-2000 RPM for 2 minutes. After 2 minutes, if HO2S bank 1, sensor 1 voltage rapidly swings greater than and less than .3-.6 volt, go to next step. After 2 minutes, if HO2S bank 1, sensor 1 voltage does not rapidly swing greater than and less than .3-.6 volt, go to step 5).
4. Observe scan tool with engine running at 1200-2000 RPM. If scan tool indicates closed loop operation, see DIAGNOSTIC AIDS. If scan tool does not indicate closed loop operation, go to step 8).
5. If HO2S bank 1, sensor 1 voltage remains within .3-.6 volt longer than it swings outside of .3-.6 volt range, go to step 10). If not, go to next step.
6. Check for poor connection at VCM. If a problem was found, go to step 10). If a problem was not found, go to next step.
7. Check for poor connection at HO2S bank 1, sensor 1. If a problem was found, go to step 10). If a problem was not found, go to next step.
8. Replace HO2S bank 1, sensor 1. After replacing HO2S sensor, go to step 10).
9. Check leaded fuel, incorrect gasket sealer and over rich operation as possible causes of HO2S contamination. If a problem was found, go to next step. If a problem was not found, go to step 11).
10. Repair or replace as necessary. After repairs, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1134. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DO NOT solder HO2S wires.

DTC P1153 - HO2S INSUFFICIENT SWITCHING BANK 2, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S is operating properly by monitoring number of lean/rich and rich/lean switches. DTC will set when the following conditions are present

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No EGR DTCs are set.
6. No ECT sensor DTCs are set.
7. No misfire DTCs are set.
8. No intrusive test in progress.
9. No device controls active.
10. System voltage is greater than or equal to 9 volts.

1. Closed-loop low MAP not active.
2. Closed-loop Mode 0 not active.
3. DTCs P0151, P0152, P0154 and P0155 not active.
4. Vehicle is in "closed-loop" operation.
5. ECT is greater than 135°F (57°C).
6. Engine run time greater than 75 seconds.
7. MAF is greater than 15 gm/s with engine at less than 3000 RPM.
8. Canister purge duty cycle is greater than zero percent.
9. Conditions are present for greater than 2 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to step 3).
3. Install scan tool. Start and idle engine. Using scan tool, monitor ECT display. Operate engine at 1200-2000 RPM for 2 minutes. After 2 minutes, if HO2S voltage is rapidly swinging between less than .30 volt to greater than .60 volt, go to next step. If HO2S voltage is not swinging as specified, go to step 5).
4. With engine running at 1200-2000 RPM, observe scan tool display. If scan tool indicates that system is in "closed loop", see DIAGNOSTIC AIDS. If system is not in "closed loop", go to step 8).
5. Check if front HO2S bank 2, sensor 1 voltage is staying within .30-.60 volts longer than it swings out of this value/range. If voltage stays within the specified range, go to step 10). If voltage does not stay within the specified range, go to next step.
6. Check VCM connector terminal contact at HO2S front high and low signal circuits. If a problem was found, go to step 10). If no problem was found, go to next step.
7. Check for poor connection at HO2S bank 2, sensor 1 connector. If a problem was found, go to step 10). If no problem was found, go to next step.
8. Replace HO2S. After replacing HO2S sensor, go to step 11).
9. Check for cause of sensor contamination, i.e., leaded fuel, incorrect gasket sealer, or over-rich operation. If a problem was found, go to next step. If no problem was found, go to step 11).
10. Repair or replace as necessary. After repairs, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1153. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check HO2S heater operation. Never solder HO2S wires.

DTC P1154 - HO2S TRANSITION TIME RATIO BANK 2, SENSOR 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

This diagnostic test is used in conjunction with HO2S bank 2, sensor 1 slow response diagnostic test P0153. Ratio of response times that were calculated are compared to calibrated limits. If number of lean to rich and rich to lean transitions were zero, ratios will be set to zero. Otherwise, ratio is calculated based on which average response time was greater. DTC will set when the following conditions are present

1. No TP sensor DTCs are set.
2. No EVAP DTCs are set.
3. No IAT sensor DTCs are set.
4. No MAP sensor DTCs are set.
5. No EGR DTCs are set.
6. No ECT sensor DTCs are set.
7. No misfire DTCs are set.
8. No intrusive test in progress.
9. No device controls active.
10. System voltage is greater than or equal to 9 volts.

1. Closed-loop low MAP not active.
2. Closed-loop Mode 0 not active.
3. DTCs P0151, P0152, P0154 and P0155 not active.
4. Vehicle is in "closed-loop" operation.
5. ECT is greater than 135°F (57°C).
6. Engine run time greater than 75 seconds.
7. MAF is greater than 15 gm/s with engine at less than 3000 RPM.
8. Canister purge duty cycle is greater than zero percent.
9. Conditions are present for greater than 2 seconds.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
3. Start engine and warm engine to normal operating temperature. Observe engine coolant temperature using scan tool while operating engine at a steady speed of 1200-2000 RPM for 2 minutes. After 2 minutes, if HO2S bank 2, sensor 1 voltage rapidly swings greater than and less than .3-.6 volt, go to next step. After 2 minutes, if HO2S bank 2, sensor 1 voltage does not rapidly swing greater than and less than .3-.6 volt, go to step 5).
4. Observe scan tool with engine running at 1200-2000 RPM. If scan tool indicates closed loop operation, see DIAGNOSTIC AIDS. If scan tool does not indicate closed loop operation, go to step 8).
5. Check if HO2S bank 2, sensor 1 voltage remains within .3-.6 volt longer than it swings outside of .3-.6 volt. If voltage remains within specification longer, go to step 10). If voltage does not remain within specification longer, go to next step.
6. Check for poor connection at VCM. If a problem was found, go to step 10). If a problem was not found, go to next step.
7. Check for poor connection at HO2S bank 2, sensor 1. If a problem was found, go to step 10). If a problem was not found, go to next step.
8. Replace HO2S. After replacing HO2S sensor, go to step 11).
9. Check leaded fuel, incorrect gasket sealer and over rich operation as possible causes of HO2S contamination. If a problem was found, go to next step. If a problem was not found, go to step 11).
10. Repair or replace as necessary. After repairs, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1154. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check HO2S heater operation. DO NOT solder HO2S wires.

DTC P1345 - CRANKSHAFT/CAMSHAFT POSITION SENSOR CORRELATION

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

DTC determines if distributor is installed incorrectly, or if a mechanical malfunction is present in engine.

1. When engine is running, cam sensor reference pulse is not detected at correct relative position with crank pulse.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start engine. Using scan tool, monitor engine RPM. If engine RPM fluctuates up to twice the expected RPM, go to next step. If engine RPM does not fluctuate up to twice the expected RPM, go to step 4).
3. Replace crankshaft position sensor. After replacing sensor, go to step 6).
4. Check for proper installation of distributor. If a problem was found, go to next step. If a problem was not found, go to step 6).
5. Repair as necessary. After repairs, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1345. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DTC P1351 - IGNITION CONTROL (IC) CIRCUIT HIGH VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Enhanced ignition system provides timing input to VCM with a crank sensor. VCM utilizes reference pulse to determine individual ignition spark timing for each cylinder.

Once VCM calculates ignition timing, timing signal is sent to ignition coil module. Each timing pulse received by ignition coil module triggers module operation of ignition coil. Secondary ignition voltage is induced then sent to distributor for distribution to each spark plug. IC signal voltage ranges from about 0.5 volt to 4.5 volts.

1. Voltage on IC circuit is greater than 4.9 volts and engine speed less than 250 RPM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Clear DTCs. Disconnect injector connector. Crank engine for 30 seconds. Check if DTC P1351 is set. If DTC P1351 is set, go to next step. If DTC P1351 is not set, see DIAGNOSTIC AIDS.
3. Turn ignition off. Reconnect injector connector. Disconnect ignition coil module connector. Using DVOM, probe ignition coil module connector terminal "B" (engine harness side) to ground. With DVOM on AC scale, crank engine and note voltage reading. If voltage is 1-4 volts, go to step 9). If voltage is not 1-4 volts, go to next step.
4. Turn ignition off. Disconnect Gray VCM connector. Using DVOM, check resistance between IC control circuit of VCM and ignition coil module connector terminal "B". If resistance is 10 ohms, go to step 6). If resistance is not 10 ohms, go to next step.
5. Repair open in IC control circuit between VCM and ignition coil module. Go to step 16).
6. Check for poor connection at VCM. If a problem was found, go to next step. If a problem was not found, go to step 8).
7. Repair VCM connection. After repairs, go to step 16).
8. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to step 16).
9. Turn ignition off. Using test light, probe ignition coil module connector terminal "C" (engine harness side) to battery voltage. If test light illuminates, go to step 11). If test light does not illuminate, go to next step.
10. Repair open in ignition coil module ground circuit. After repairs, go to step 16).
11. Turn ignition on. Using test light, probe ignition coil module connector terminals "D" and "A" (engine harness side) to ground. If test light illuminates for both terminals, go to step 13). If test light does not illuminate for both terminals, go to next step.
12. Repair ignition coil module ignition feed circuit. Go to step 16).
13. Check for poor connection at ignition coil module. If a problem was found, go to step 15). If a problem was not found, go to next step.
14. Replace ignition coil module. After replacing module, go to step 16).
15. Repair ignition coil module connection. After repairs, go to next step.
16. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1351. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect VCM harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

If connections and harness are okay, using DVOM connected between ignition feed circuit and IC control circuit of VCM connector, monitor voltage while wiggling related connectors and wiring harness. If a failure is induced, voltage will change. A change in voltage will assist in isolating location of fault.

DTC P1361 - IGNITION CONTROL (IC) CIRCUIT LOW VOLTAGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Enhanced ignition system provides timing input to VCM with a crank sensor. VCM utilizes reference pulse to determine individual ignition spark timing for each cylinder.

Once VCM calculates ignition timing, timing signal is sent to ignition coil module. Each timing pulse received by ignition coil module triggers module operation of ignition coil. Secondary ignition voltage is induced then sent to distributor for distribution to each spark plug. IC signal voltage ranges from about 0.5 volt to 4.5 volts.

1. Voltage on ignition control circuit is less than .04 volt and engine speed is less than 3000 RPM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Clear DTCs. Disconnect injector connector. Crank engine for 15 seconds. Check if DTC P1361 is set. If DTC P1361 is set, go to next step. If DTC P1361 is not set, see DIAGNOSTIC AIDS.
3. Turn ignition off. Reconnect injector connector. Disconnect ignition coil module connector. Using DVOM, probe ignition coil module connector terminal "B" (engine harness side) to ground. With DVOM on AC scale, crank engine and note voltage reading. If voltage is 1-4 volts, go to step 9). If voltage is not 1-4 volts, go to next step.
4. Turn ignition off. Disconnect Gray VCM connector. Using test light, probe IC control circuit of VCM connector to battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 6).
5. Repair short to ground in IC control circuit. After repairs, go to step 14).
6. Using test light, probe IC control circuit of VCM connector to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
7. Repair short to voltage in IC control circuit. After repairs, go to step 14).
8. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to step 14).
9. Turn ignition off. Using test light, probe ignition coil module connector terminal "C" (engine harness side) to battery voltage. If test light illuminates, go to step 11). If test light does not illuminate, go to next step.
10. Repair open in ignition coil module ground circuit. Go to step 14).
11. Check for poor connection at ignition coil module. If a problem was found, go to step 13). If a problem was not found, go to next step.
12. Replace ignition coil module. After replacing module, go to step 14).
13. Repair ignition coil module connection. After repairs, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1361. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect VCM harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

If connections and harness are okay, using DVOM connected between ignition feed circuit and IC control circuit of VCM connector, monitor voltage while wiggling related connectors and wiring harness. If a failure is induced, voltage will change. A change in voltage will assist in isolating location of fault.

DTC P1380 - ELECTRONIC BRAKE CONTROL MODULE (EBCM) DTC DETECTED ROUGH ROAD DATA UNUSABLE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

This diagnostic determines if ABS is capable of detecting a rough road situation.

1. Vehicle speed is at least one MPH.
2. Engine speed is less than 5800 RPM.
3. Engine load is not greater than 89.9 percent.
4. DTC P0300 is set and requesting MIL on.
5. Rough road indicator not being sent by EBCM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Turn ignition off. Disconnect VCM and EBCM connectors. Using DVOM, check for open in serial data circuit between VCM and EBCM. If a problem is found, go to next step. If a problem was not found, see the BRAKES SYSTEM - ANTI-LOCK article in the BRAKES section.
3. Repair as necessary. After repairs, go to next step.
4. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1380. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, DTC is intermittent.
5. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DTC P1381 - ELECTRONIC BRAKE CONTROL MODULE (EBCM) VCM SERIAL DATA

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

This diagnostic determines a serial data malfunction which could inhibit transfer of ABS rough road data to VCM.

1. DTC P0300 is set and requesting MIL on.
2. No rough road data is available from EBCM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Turn ignition off. Disconnect VCM and EBCM connectors. Using DVOM, check for open in serial data circuit between VCM and EBCM. If a problem is found, go to next step. If a problem was not found, see the BRAKES SYSTEM - ANTI-LOCK article in the BRAKES section.
3. Repair as necessary. After repairs, go to next step.
4. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1381. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, DTC is intermittent.
5. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DTC P1406 - EGR VALVE PINTLE POSITION CIRCUIT

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM constantly monitors linear EGR valve pintle position sensor to ensure valve is responding properly to commands from VCM.

1. EGR pintle position signal indicates a voltage out of normal range of pintle position sensor, or a signal that is 10 percent greater or less than VCM commanded position.
2. Ignition voltage is greater than 9 volts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, monitor EGR pintle position. If scan tool indicates zero percent, go to next step. If scan tool does not indicate zero percent, go to step 8).
3. Start engine. Using scan tool, select MISCELLANEOUS TESTS, EGR CONTROL and cycle EGR valve through 25, 50, 75 and 100 percent positions while observing DESIRED EGR POSITION and ACTUAL EGR POSITION. If positions are close to commanded positions, see DIAGNOSTIC AIDS. If positions are not close to commanded positions, go to next step.
4. Turn ignition off. Disconnect EGR valve connector. Turn ignition on, with engine off. Connect test light between control circuit and ignition feed circuit of EGR valve connector. Using scan tool, command EGR position to 100 percent. If test light illuminates, go to step 26). If test light does not illuminate, go to next step.
5. Using test light, probe ignition feed circuit of EGR valve connector to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
6. Check for poor connections at VCM and EGR valve. Also, check for open in ground circuit. If a problem is found, go to next step. If a problem is not found, go to step 8).
7. Repair VCM and EGR valve connections or open in ground circuit. After repairs, go to step 40).
8. Turn ignition off. Install scan tool. Disconnect EGR valve connector. Turn ignition on, with engine off. Using scan tool, monitor EGR pintle position. If scan tool indicates zero percent, go to step 16). If scan tool does not indicate zero percent, go to next step.
9. Check if DTC P0108 is also set. If DTC P0108 is set, go to «DTC P0108»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series__dtc-p0108-map-sensor-circuit) . If DTC P0108 is not set, go to next step.
10. Check for short to voltage in pintle position circuit. If a problem was found, go to next step. If a problem was not found, go to step 12).
11. Repair short to voltage in pintle position circuit. Go to step 40).
12. Check if 20-amp ENG-1 fuse is blown. If fuse is blown, go to step 13). If fuse is not blown, go to step 15).
13. Replace 20-amp ENG-1 fuse. After replacing fuse, go to next step.
14. Repair short to ground in ignition feed circuit. After repairs, go to step 40).
15. Repair open in ignition feed circuit. After repairs, go to step 40).
16. Using test light, probe ground circuit of EGR valve connector to battery voltage. If test light illuminates, go to step 19). If test light does not illuminate, go to next step.
17. Check for open in ground circuit. If a problem was found, go to next step. If a problem was not found, go to step 19).
18. Repair open in ground circuit. After repairs, go to step 40).
19. Using test light, probe control circuit of EGR valve connector to battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 23).
20. Unplug VCM. With test light connected to battery voltage, probe EGR valve harness connector control circuit terminal. If test light is on, go to next step. If not, go to step 39).
21. Check for short to ground in control circuit. If a problem was found, go to next step. If a problem was not found, go to step 23).
22. Repair short to ground in control circuit. After repairs, go to step 40).
23. Check for poor connection at EGR valve. If a problem was found, go to next step. If a problem was not found, go to step 25).
24. Repair EGR valve connection. After repairs, go to step 40).
25. Replace EGR valve. After replacing EGR valve, go to step 40).
26. Using DVOM, check voltage between ground circuit and 5-volt reference circuit of EGR valve connector. If voltage is about 5 volts, go to step 31). If voltage is not about 5 volts, go to next step.
27. Using DVOM, check voltage between 5-volt reference circuit of VCM connector and ground. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 29).
28. Check for poor connection at VCM. If a problem was found, go to next step. If a problem was not found, go to step 30).
29. Repair VCM connection. After repairs, go to step 40).
30. Repair open in 5-volt reference circuit. After repairs, go to step 40).
31. Using test light, probe pintle position circuit of EGR valve connector to battery voltage. If test light illuminates, go to step 34). If test light does not illuminate, go to next step.
32. Check for short to ground in pintle position circuit. If a problem was found, go to next step. If a problem was not found, go to step 34).
33. Repair short to ground in pintle position circuit. After repairs, go to step 40).
34. Using Connector Test Kit (J 35616-A), install adapters in all circuits between engine harness connector and EGR valve connector. Connect DVOM between pintle position circuit of EGR valve connector and ground. Using scan tool, command EGR position to 100 percent. Observe voltage when EGR is commanded on. If voltage is 3.5-5 volts, go to next step. If voltage is not 3.5-5 volts, go to step 36).
35. Check for open in pintle position circuit. Also, check for poor connection at EGR valve. If a problem was found, go to step 37). If a problem was not found, go to next step.
36. Check for poor connection at VCM. If a problem was found, go to step 37). If a problem was not found, go to step 39).
37. Repair open in pintle position circuit. After repairs, go to step 40).
38. Repair VCM connection. After repairs, go to step 40).
39. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to step 41).
40. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1406. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
41. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect VCM harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

If connections and harness are okay, using DVOM connected between affected terminals and ground, monitor voltage while wiggling related connectors and wiring harness. If a failure is induced, voltage will change. A change in voltage will assist in isolating location of fault.

DTC P1415 - AIR SYSTEM BANK 1

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

A fused ignition voltage is supplied to AIR relay. VCM controls AIR pump by grounding AIR relay control circuit which energizes relay and supplies voltage to AIR pump clutch. When fuel system goes to closed loop, VCM opens ground to AIR control circuit. DTC will set when the following conditions are present

AIR Passive Test Enable

1. No ECT sensor DTCs are set.
2. No IAC DTCs are set.
3. No HO2S DTCs are set.
4. No misfire DTCs are set.
5. No MAP sensor DTCs are set.
6. No fuel trim DTCs are set.
7. No EVAP DTCs are set.
8. No TP sensor DTCs are set.
9. No IAT DTCs are set.
10. No MAF DTCs are set.
11. System voltage greater than 10 volts for a period greater than 3 seconds.
12. IAT greater than 0°C.
13. Engine run time greater than 3 seconds.

AIR Active Test Enable

1. AIR passive test failed
2. No IAC DTCs are set.
3. No HO2S DTCs are set.
4. No misfire DTCs are set.
5. No MAP sensor DTCs are set.
6. No fuel trim DTCs are set.
7. No EVAP DTCs are set.
8. No TP sensor DTCs are set.
9. No IAT DTCs are set.
10. No MAF DTCs are set.
11. Power enrichment not active.
12. Decel fuel cut-off not active.
13. Air/Fuel ratio at 14.7:1.
14. Engine speed is greater than or equal to 550 RPM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Install scan tool. Start and run engine for greater than 2 minutes. Ensure engine is operating at normal operating temperature. Using scan tool, command AIR pump on. If bank 1 short term fuel trim indicates a change of greater than 6 percent, go to next step. If bank 1 short term fuel trim does not indicate a change of greater than 6 percent, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Disconnect bank 1 AIR crossover hose from AIR valve. Using scan tool, command AIR pump on. Observe if air flows from AIR valve. If air flows from valve, go to next step. If air does not flow from valve, go to step 7).
5. Check for restrictions or leaks in bank 1 AIR pipe, hoses and fittings. If a problem was found, go to next step. If a problem was not found, go to step 2).
6. Repair as necessary. After repairs, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1415. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for worn or loose AIR pump drive belt. Check for pinched, kinked or restricted AIR pipes, hoses or fittings.

DTC P1416 - AIR SYSTEM BANK 2

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

A fused ignition voltage is supplied to AIR relay. VCM controls AIR pump by grounding AIR relay control circuit which energizes relay and supplies voltage to AIR pump clutch. When fuel system goes to closed loop, VCM opens ground to AIR control circuit. DTC will set when the following conditions are present

1. No ECT sensor DTCs are set.
2. No IAC DTCs are set.
3. No HO2S DTCs are set.
4. No misfire DTCs are set.
5. No MAP sensor DTCs are set.
6. No fuel trim DTCs are set.
7. No EVAP DTCs are set.
8. No TP sensor DTCs are set.
9. No IAT DTCs are set.
10. No MAF DTCs are set.
11. System voltage greater than 10 volts for a period greater than 3 seconds.
12. IAT greater than 0°C.
13. Engine run time greater than 3 seconds.

1. AIR passive test failed
2. No IAC DTCs are set.
3. No HO2S DTCs are set.
4. No misfire DTCs are set.
5. No MAP sensor DTCs are set.
6. No fuel trim DTCs are set.
7. No EVAP DTCs are set.
8. No TP sensor DTCs are set.
9. No IAT DTCs are set.
10. No MAF DTCs are set.
11. Power enrichment not active.
12. Decel fuel cut-off not active.
13. Air/Fuel ratio at 14.7:1.
14. Engine speed is greater than or equal to 550 RPM.
15. "Closed loop" for a period of greater than 15 seconds.
16. Engine load less than 50 percent.
17. MAF less than or equal to 100 gm/s.
18. System voltage is greater than 10 volts.
19. ECT greater than or equal to 167°F (75°C) but less than 221°F (105°C).
20. IAT greater than 0°C.
21. Integrator greater than .95 but less than 1.0 for 3 seconds.

1. Perform Powertrain On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
2. Install scan tool. Start and run engine for greater than 2 minutes. Ensure engine is operating at normal operating temperature. Using scan tool, command AIR pump on. If bank 2 short term fuel trim indicates a change of greater than 6 percent, go to next step. If bank 2 short term fuel trim does not indicate a change of greater than 6 percent, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Disconnect bank 2 AIR crossover hose from AIR valve. Using scan tool, command AIR pump on. Observe if air flows from AIR valve. If air flows from valve, go to next step. If air does not flow from valve, go to step 7).
5. Check for restrictions or leaks in bank 2 AIR pipe, hoses and fittings. If a problem was found, go to next step. If a problem was not found, go to step 2).
6. Repair as necessary. After repairs, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1416. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for worn or loose AIR pump drive belt. Check for pinched, kinked or restricted AIR pipes, hoses or fittings.

DTC P1441 - EVAP EMISSION SYSTEM FLOW DURING NON-PURGE

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Canister purge is controlled by a solenoid valve that allows ported vacuum to purge canister when energized. VCM supplies ground to energize solenoid valve which is pulse width modulated. Duty cycle is determined by closed loop feedback from HO2S. Duty cycle is calculated by VCM and output is commanded when certain conditions have been met.

A vacuum switch in purge line is used to detect when system is being purged. Normally closed switch will open when less than one in. Hg is present in purge line. VCM supplies a 12-volt reference to switch to monitor if evaporative emission control system is operating properly. DTC will set if switch is open when VCM is not commanding purge.

1. EVAP vacuum switch state equals high vacuum for a period greater than 4 seconds.
2. Purge solenoid diagnostic vacuum switch DTC is not set.
3. No IAC DTCs are set.
4. No MAP sensor DTCs are set.
5. No TP sensor DTCs are set.
6. No EGR DTCs are set.
7. BARO is greater than 75 kPa.
8. Engine coolant temperature is less than 230°F (110°C).
9. Intake air temperature is less than 194°F (90°C).
10. Difference between engine coolant temperature and intake air temperature is less than 194°F (90°C).
11. Purge DC is less than or equal to 5 percent.
12. Manifold absolute pressure is greater than 20 kPa but less than 80 kPa.
13. Throttle positions is greater than 5 percent but less than 60 percent.
14. Engine speed is greater than 800 RPM but less than 3000 RPM.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. If DTC P0107 is also set, diagnose that DTC first. If DTC P0107 is not set, turn ignition on with engine off. Using scan tool, command EVAP canister purge solenoid valve on and off. If valve clicks when commanded on and off, go to step 5). If valve does not click when commanded on and off, go to next step.
3. Unplug EVAP solenoid valve connector. Connect test light between connector terminals. Command solenoid on and off with scan tool. If test light turns on and off, go to next step. If test light does not turn on and off, go to step 15).
4. Replace EVAP solenoid. After repairs, go to step 16).
5. With ignition on and engine off, check scan tool EVAP duty cycle. If duty cycle is zero percent, see DIAGNOSTIC AIDS. If duty cycle is not zero percent, go to next step.
6. Unplug EVAP vacuum switch connector. Monitor scan tool. If scan tool displays PURGE, go to next step. If scan tool does not display PURGE, go to step 11).
7. Connect jumper wire between EVAP vacuum switch connector terminals. If scan tool reads NO PURGE, go to next step. If scan tool does not read NO PURGE, go to step 11).
8. Check sensor connections. If a problem is found, go to next step. If problem is not found, go to step 10).
9. Repair sensor connections. After repairs, go to step 16).
10. Replace sensor. After replacing sensor, go to step 16).
11. With DVOM to ground, check voltage on EVAP vacuum switch signal circuit terminal. If voltage is about 12 volts, go to next step. If voltage is not about 12 volts, go to step 14).
12. Check for open ground circuit and/or faulty connection. If a problem exists, go to next step. If no problem exists, go to step 15).
13. Repair ground circuit as necessary. After repairs, go to step 16).
14. Repair open in 12-volt signal circuit. After repairs, go to step 16).
15. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
16. Using a scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1441. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

DTC P1508 - IDLE AIR CONTROL SYSTEM LOW RPM

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM controls idle speed with an Idle Air Control (IAC) valve to a calculated desired RPM based on sensor inputs and actual engine RPM. VCM uses 4 circuits to move an IAC valve, allowing varying amounts of airflow into intake manifold.

To increase idle RPM, VCM moves IAC valve out, allowing more air to by-pass throttle plate. To decrease RPM, VCM moves IAC valve in, reducing amount of air by-passing throttle plate. Scan tool reads VCM commands to IAC valve in counts. The higher the counts, the more air that is allowed to by-pass throttle plate (higher idle). The lower the counts, less air is allowed to by-pass throttle plates (lower idle). DTC will set when the following conditions are present

Passive Test

1. No TP sensor DTCs are set.
2. No ECT sensor DTCs are set.
3. No VSS DTCs are set.
4. No MAP sensor DTCs are set.
5. ECT is greater than 122°F (50°C).
6. IAT is greater than -13°F (-25°C).
7. BARO is greater than 70 kPa (less than 10,300 ft.).
8. Vehicle speed is less than 2 MPH.
9. System voltage is greater than 10 volts but less than 18 volts.
10. Engine run time is greater than 30 seconds.
11. Throttle position is less than one percent.
12. All conditions are met for greater than 3 seconds.
13. Change in calculated airflow is greater than 2 counts.

Active Test

1. Calculated air flow is 17.5-37.5 gm/s.
2. Vehicle speed is 35-85 MPH.
3. Change in TP sensor is less than one percent.
4. Change in engine speed is less than 30 RPM.
5. IAC motor commanded to 10 percent for 100 milliseconds.
6. Change in calculated airflow is greater than 2 counts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Turn ignition off. Connect IAC driver to IAC valve. Apply parking brake and block wheels. Ensure A/C is off. Operate engine at idle with transmission in Park (A/T) or Neutral (M/T). Install scan tool and display RPM. Using IAC driver, extend and retract IAC valve. Observe RPM display on scan tool. If engine RPM decreases and increases as IAC is cycled, go to next step. If engine RPM does not decreases and increases as IAC is cycled, go to step 4).
3. Observe RPM display on scan tool. RPM should change smoothly from 700 RPM to 1500 RPM with each flash of IAC driver light. If RPM changes smoothly as specified, go to step 5). If RPM does not change smoothly as specified, go to next step.
4. Check IAC passages. If IAC passages are okay, replace IAC valve. Perform IAC reset procedure if IAC valve is replaced. See the ADJUSTMENTS article. Go to step 12).
5. Install appropriate IAC Node Light (J 37027-A) in VCM harness. Cycle IAC driver and observe lights. As RPM is changed over its range, both lights should cycle Green and Red, but never off. If both Green and Red lights flash on and off, go to step 8). If both Green and Red lights does not flash on and off, go to next step.
6. Check for the following conditions: Faulty connector terminal contacts. Open circuits including connections. Circuits shorted to ground or voltage. Faulty VCM connection. If a problem was found, go to next step. If a problem was not found, go to step 11).
7. Repair connections and terminal contacts as necessary. After repairs, go to step 12).
8. Using other connector on IAC driver pigtail, check resistance of IAC coils. Check resistance between IAC coil terminals "A" and "B" and terminals "C" and "D". Resistance should be 40-80 ohms. If resistance is as specified, go to next step. If resistance is not as specified, go to step 10).
9. Check resistance between IAC coil terminals "A" and "C" and terminals "B" and "D". Resistance should be infinite. If resistance is as specified, see DIAGNOSTIC AIDS. If resistance is not as specified, go to next step.
10. Replace IAC valve. Perform IAC reset procedure if IAC valve is replaced. See the ADJUSTMENTS article. After replacing IAC valve, go to step 12).
11. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1508. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DTC could be caused by an IAC valve which is stopped and cannot respond to VCM, a throttle stop screw which has been tampered with, or a damaged throttle or linkage.

A slow, unstable or fast idle could be caused by a non-IAC valve system problem that cannot be overcome by IAC valve. See the TESTS W/O CODES article. Out of range control IAC scan tool counts will be greater than 60 if idle is too low and zero if idle is too high. Check for fuel system too lean and rich. Check throttle body bore for foreign material. IAC reset is done with scan tool miscellaneous functions mode.

DTC P1509 - IDLE AIR CONTROL SYSTEM HIGH RPM

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

VCM controls idle speed with an Idle Air Control (IAC) valve to a calculated desired RPM based on sensor inputs and actual engine RPM. VCM uses 4 circuits to move an IAC valve, allowing varying amounts of airflow into intake manifold.

To increase idle RPM, VCM moves IAC valve out, allowing more air to by-pass throttle plate. To decrease RPM, VCM moves IAC valve in, reducing amount of air by-passing throttle plate. Scan tool reads VCM commands to IAC valve in counts. The higher the counts, the more air that is allowed to by-pass throttle plate (higher idle). The lower the counts, less air is allowed to by-pass throttle plates (lower idle). DTC will set when the following conditions are present

1. No TP sensor DTCs are set.
2. No ECT sensor DTCs are set.
3. No VSS DTCs are set.
4. No MAP sensor DTCs are set.
5. Engine coolant temperature is greater than 162°F (72°C).
6. Intake air temperature is greater than -13°F (-25°C).
7. BARO is greater than 70 kPa (less than 10,300 ft.).
8. Vehicle speed is less than 2 MPH.
9. System voltage is greater than 10 volts but less than 18 volts.
10. Engine run time is greater than 30 seconds.
11. Throttle position is less than one percent.
12. All conditions are met for greater than 3 seconds.
13. Change in calculated airflow is greater than 2 counts.

1. Calculated airflow is 17.5-37.5 gm/s.
2. Vehicle speed is 35-85 MPH.
3. Change in TP sensor is less than one percent.
4. Change in engine speed is less than 30 RPM.
5. IAC motor commanded to 10 percent for 100 milliseconds.
6. Change in calculated air flow is greater than 2 counts.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «F - BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article. After performing OBD system check, go to next step.
2. Turn ignition off. Connect IAC driver to IAC valve. Apply parking brake and block wheels. Ensure A/C is off. Operate engine at idle with transmission in Park (A/T) or Neutral (M/T). Install scan tool and display RPM. Using IAC driver, extend and retract IAC valve. Observe RPM display on scan tool. If engine RPM decreases and increases as IAC is cycled, go to next step. If engine RPM does not decreases and increases as IAC is cycled, go to step 4).
3. Observe RPM display on scan tool. RPM should change smoothly from 700 RPM to 1500 RPM with each flash of IAC driver light. If RPM changes smoothly as specified, go to step 5). If RPM does not change smoothly as specified, go to next step.
4. Check IAC passages. If IAC passages are okay, replace IAC valve. Perform IAC reset procedure if IAC valve is replaced. See the ADJUSTMENTS article. After replacing IAC valve, go to step 12).
5. Install appropriate IAC Node Light (J 37027-A) in VCM harness. Cycle IAC driver and observe lights. As RPM is changed over its range, both lights should cycle Green and Red, but never off. If both cycle Green and Red, go to step 8). If both Green and Red lights does not flash on and off, go to next step.
6. Check for the following conditions: Faulty connector terminal contacts. Open circuits including connections. Circuits shorted to ground or voltage. Faulty VCM connection. If a problem was found, go to next step. If a problem was not found, go to step 11).
7. Repair connections and terminal contacts as necessary. After repairs, go to step 12).
8. Using other connector on IAC driver pigtail, check resistance of IAC coils. Check resistance between IAC coil "B" hi and IAC coil "B" lo circuits at IAC terminals. Also, check resistance between IAC coil "A" hi and IAC coil "A" lo circuits at IAC terminals. Resistance should be 40-80 ohms. If resistance is as specified, go to next step. If resistance is not as specified, go to step 10).
9. Check resistance between IAC coil "B" hi and IAC coil "A" lo circuits at IAC terminals. Also, check resistance between IAC coil "B" lo and IAC coil "A" hi circuits at IAC terminals. Resistance should be infinite. If resistance is as specified, see DIAGNOSTIC AIDS. If resistance is not as specified, go to next step.
10. Replace IAC valve. Perform IAC reset procedure if IAC valve is replaced. See the ADJUSTMENTS article. After replacing IAC valve, go to step 12).
11. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1509. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DTC could be caused by an IAC valve which is stopped and cannot respond to VCM, a throttle stop screw which has been tampered with, or a damaged throttle or linkage.

A slow, unstable or fast idle could be caused by a non-IAC valve system problem that cannot be overcome by IAC valve. See the TESTS W/O CODES article. Out of range control IAC scan tool counts will be greater than 60 if idle is too low and zero if idle is too high. Check for fuel system too lean and rich. Check throttle body bore for foreign material. IAC reset is done with scan tool miscellaneous functions mode.

See also:
• F - BASIC TESTING - 5.7L
• CONNECTOR IDENTIFICATION -- G VANS
• DIAGNOSTIC PROCEDURE
• HARD OR INTERMITTENT TROUBLE CODE DETERMINATION
• P0101
• P0102
• P0103
• P0106
• P0107
• P0108
• P0112
• P0113
• P0117
• P0118
• P0121
• P0122
• P0123
• P0125
• P0131
• P0132
• P0133
• P0134
• P0135
• P0137
• P0138
• P0140
• P0141
• P0143
• P0144
• P0146
• P0147
• P0151
• P0152
• P0153
• P0154
• P0155
• P0171
• P0172
• P0174
• P0175
• P0300
• P0301
• P0302
• P0303
• P0304
• P0305
• P0306
• P0307
• P0308
• P0325
• P0327
• P0336
• P0337
• P0338
• P0339
• P0340
• P0341
• P0401
• P0420
• P0430
• P0441
• P0500
• P0506
• P0507
• P1106
• P1107
• P1111
• P1112
• P1114
• P1115
• P1121
• P1122
• P1133
• P1134
• P1153
• P1154
• P1345
• P1351
• P1361
• P1380
• P1381
• P1406
• P1415
• P1416
• P1441
• P1508
• P1509
• CLEARING DIAGNOSTIC TROUBLE CODES (DTC)
• SCAN DATA
• CONNECTOR IDENTIFICATION
• IAT TEMPERATURE-TO-RESISTANCE VALUES