Engine Controls - Tests W/codes - v8 Chevrolet Cutaway P30

INTRODUCTION

Most engine control problems result from mechanical failures, poor electrical connections or damaged vacuum hoses. Before condemning the computer system, perform checks and inspections covered in BASIC TESTING article in this section. Failure to do so may result in lost diagnostic time.

If no faults were found while performing BASIC TESTING, proceed with DIAGNOSTIC PROCEDURE. If no fault codes or only a non-running Code 12 is present and driveability problems exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in TESTS W/O CODES article in this section.

TERMINOLOGY

Due to Federal government requirements, manufacturers may use names and acronyms for systems and components different than those used in previous years. The following table will help eliminate confusion when dealing with these components and systems. Only relevant components and systems whose names have changed from current General Motors Corp. terminology have been listed.

SAE TERMINOLOGY

SELF-DIAGNOSTIC SYSTEM

All vehicle are equipped with either an Electronic Control Module (ECM), Powertrain Control Module (PCM) or Vehicle Control Module (VCM). Unless specifically stated, references to ECM also apply to PCM or VCM equipped vehicles.

The ECM is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, ECM will illuminate the SERVICE ENGINE SOON light located on instrument panel. This light is also referred to as the Malfunction Indicator Light (MIL). When malfunction is detected and MIL is turned on, a corresponding trouble code will be stored in ECM memory. To retrieve stored codes, see READING TROUBLE CODES or RETRIEVING CODES (NON-SCAN) . Malfunctions are recorded as HARD FAILURES or as INTERMITTENT FAILURES.

HARD FAILURES

Hard failures cause MIL to illuminate and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause must be found using diagnostic (code) charts. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but driveability can be poor.

INTERMITTENT FAILURES

Intermittent failures cause MIL to flicker or illuminate and go out about 10 seconds after the intermittent fault goes away. The corresponding trouble code, however, will be retained in ECM memory. If related fault does not reoccur within 50 engine restarts, it will be erased from ECM memory. Intermittent failures may be caused by faulty sensor, connector or wiring. See INTERMITTENTS in TESTS W/O CODES article in this section.

DIAGNOSTIC PROCEDURE

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

1. Ensure all engine systems not related to the computer are operating properly. DO NOT proceed with testing unless all other problems have been repaired. Perform diagnostic circuit check before using trouble code charts. See BASIC TESTING article in this section.
2. If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent. Hard codes cause Malfunction Indicator Light (MIL) to illuminate continuously with engine running. See «HARD OR INTERMITTENT TROUBLE CODE DETERMINATION»(/chevrolet/cutaway-p30/1988-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-v8__hard-or-intermittent-trouble-code-determination) . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in TESTS W/O CODES article in this section. Exceptions are Code 13, 15, 24, 44 and 45 charts, which can help diagnose intermittent codes.
3. If trouble codes were not displayed and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. From there you will be sent to the appropriate area in I - SYS/COMP TESTS article in this section.
4. After repairs are made, clear trouble codes and perform FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

RETRIEVING CODES (NON-SCAN)

Note. The Assembly Line Data Link (ALDL) connector may also be referred to as the Data Link Connector (DLC) in flow charts. This is the same connector.

1. Turn ignition on with engine off. Malfunction Indicator Light (MIL) should glow. Locate Data Link Connector (DLC), attached to ECM wiring harness. Most DLCs are located under dash on driver's side of vehicle. For exact location of DLC, see appropriate COMPONENT LOCATIONS illustration in I - SYS/COMP TESTS article in this section. Turn ignition on. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of DLC. (Scheme 337) NOTE: Inserting jumper wire into test and ground terminals of DLC with engine running will cause fuel-injected vehicles to enter field service mode and codes will not flash. See FIELD SERVICE MODE in BASIC TESTING article in this section.
2. Malfunction Indicator Light (MIL) should flash codes. Each code is flashed 3 times. If codes DO NOT flash, perform DIAGNOSTIC CIRCUIT CHECK (GASOLINE) in BASIC TESTING article in this section. To exit diagnostic mode, turn ignition off and remove jumper wire from DLC.

Scheme 337

READING TROUBLE CODES

Note. Trouble codes retrieved from ECM/PCM/VCM may be related to either engine or transmission. For engine-related codes, use this article. For transmission-related codes, see G - TRANS. TESTS W/ CODES article in this section. To identify whether codes relate to transmission or engine, see TROUBLE CODE IDENTIFICATION table.

The ECM stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Read trouble codes by counting Malfunction Indicator Light (MIL) flashes or with diagnostic scan tester connected to the Data Link Connector (DLC). The tester is faster, and capable of reading information which would require testing individual ECM and sensor/solenoid connector terminals with a digital voltmeter. See SCAN TESTER DATA table and SCAN TESTER USAGE .

Note. When using a scan tester, there is a time delay between serial data updates. For instantaneous response, a digital voltmeter must be used.

If scan tester is not available, MIL flashes can be read by grounding DLC terminal with ignition on and engine off. For example, FLASH, FLASH, pause, FLASH, longer pause, indicates Code 21. The first series of flashes are the first digit of trouble code. The second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest code. Each code is displayed 3 times and will continue as long as DLC is grounded.

Note. Trouble codes will be recorded at various operating times. Some codes require sensor or switch operation for 5 seconds and others may require longer under certain conditions. Some codes may not set in a service bay operational mode.

TROUBLE CODE IDENTIFICATION

Note. Trouble code charts should only be used if Malfunction Indicator Light (MIL) is illuminated (indicating a current problem exists). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes. Anytime Code 51, 52 or 55 is displayed with another code, start with 50-series code first and proceed to lower numbered codes.

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, determine if codes are due to hard or intermittent failure. Diagnostic charts will not usually help diagnose intermittent codes. To determine hard codes and intermittent codes, proceed as follows

1. MANUALLY enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode and clear trouble codes. See «CLEARING TROUBLE CODES»(/chevrolet/cutaway-p30/1988-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-v8__clearing-trouble-codes) .
2. Apply parking brake and place transmission in Neutral or Park. Block drive wheels and start engine. MIL should go out. Run warm engine at specified curb idle for 2 minutes and note MIL.
3. If MIL comes on, manually enter diagnostic mode. Read and record trouble codes. This reveals hard failure codes. Codes 13, 15, 24, 44, 45 and 55 may require a road test to reset hard failure after trouble codes were cleared.
4. If MIL does not come on, all stored trouble codes were intermittent failures. Exceptions are noted under «DIAGNOSTIC PROCEDURE»(/chevrolet/cutaway-p30/1988-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-v8__diagnostic-procedure) .

CLEARING TROUBLE CODES

Turn ignition switch to ON position and ground diagnostic test terminal "B" at DLC. (Scheme 337) Turn ignition switch to OFF position and remove ECM fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead. Codes may also be cleared using the General Motors Tech 1 scan tester.

ECM LOCATION

For ECM locations, see appropriate COMPONENT LOCATIONS illustration in I - SYS/COMP TESTS article in this section.

Diagnostic Aids

Diagnostic aids (located in many trouble code charts) are provided as additional tips to help with diagnosis when inspected circuit is okay.

Field Service Mode Check

Malfunction Indicator Light (MIL) indicates operational mode of engine if DLC is grounded while engine is running. Light response confirms proper fuel system operation and verifies closed loop operation. Clear codes and perform this test after any repair is completed. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

SPECIAL TOOLS (DIAGNOSTIC)

Note. A special scan tester, plugged into the DLC, can read trouble codes, check system voltages on the serial data line and save a great deal of time. For additional information, see tester owner's manual. Also, see SCAN TESTER USAGE and SCAN TESTER DATA .

The computerized engine control system is most easily diagnosed using a scan tester. However, other tools may aid in diagnosing problems if a scan tester is unavailable. These tools are a tachometer, test light, ohmmeter, digital voltmeter with 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 connector 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 chart.

SCAN TESTER USAGE

Note. Before connecting scan tester, check diagnostic system and ensure accurate information is received by scan tester. Perform DIAGNOSTIC CIRCUIT (GASOLINE) CHECK in BASIC TESTING article in this section. If vehicle does not pass diagnostic circuit check, information received by scan tester may be invalid.

The scan tester is a specialized tester which can diagnose on-board computer control systems by providing almost instant access to circuit voltage information without crawling under dash or hood to backprobe sensors and connectors. scan testers reduce diagnostic time by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN TESTER DATA table.

Scan testers also furnish information on output device (solenoids and motors) status. However, status parameters are only an indication output signals have been sent to devices by the ECM. They do not indicate whether devices respond properly to that signal. This must be verified at output device using a voltmeter or test light.

Note. Code 12 should always exist when DLC test terminal is grounded with key on and engine off, but it may not be indicated by all makes of scan tester.

If trouble codes are not present, a problem may still exist. Driveability-related problems with codes displayed occur about 20 percent of the time, while driveability problems without codes occur about 80 percent of the time. Out-of-calibration sensors WILL NOT set a trouble code, but WILL cause driveability problems. A scan tester is the easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN TESTER DATA table.

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off and remove tester. Turn ignition on and ground DLC test terminal. If same codes are not flashed by Malfunction Indicator Light (MIL) as were indicated by scan tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate.

SCAN TESTER DATA

Note. Information contained in the following table is typical of readings taken on vehicle with engine idling, upper radiator hose hot, throttle closed, transmission in Park or Neutral, closed loop status achieved and all accessories off (except as noted in tables). Not all devices and systems are used on all models. For additional information, see tester owner's manual.

SCAN TESTER DATA

SUMMARY

If hard fault codes are not present and driveability symptoms or intermittent codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.), or intermittent diagnostic procedures.

Note. The following diagnostic flow charts and mini-schematics are supplied courtesy of General Motors Corp.

CODE 13, OPEN OXYGEN SENSOR CIRCUIT

When exhaust temperature is less than 600°F (316°C), O2 sensor is open and produces no voltage. An open sensor circuit or cold sensor will not allow system to enter closed loop. On 4.3L engines, oxygen sensor is equipped with an internal heating unit. This allows sensor to reach operating temperature quicker and maintain closed loop operation even during extended idle. Heating element resistance should be 3.5-14 ohms at 662°F (350°C).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 13 will set at normal operating temperature if at least 2 minutes have passed since engine start, Code 21 or 22 is not present, O2 signal voltage is steady at .35-.55 volt and throttle position sensor signal is greater than idle. All conditions must be met for at least one minute.
2. This determines if fault is in O2 sensor, ECM or wiring.
3. Use only a high-impedance Digital Volt-Ohmmeter (DVOM) while checking for continuity in signal and ground circuits. If ground circuit is open, voltage on signal circuit will be greater than .6 volt.

Verify a clean, tight connection for ground circuit No. 413. An open circuit at sensor signal terminal or ground terminal will result in a Code 13.

CODE 13 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 13, Schematic, Open Oxygen Sensor Circuit. Scheme 338

CODE 13, Flowchart, Open Oxygen Sensor Circuit. Scheme 339

CODE 14, COOLANT SENSOR SIGNAL VOLTAGE LOW

ECM uses coolant temperature sensor inputs in determining control of fuel delivery, engine timing (EST), idle (IAC) and converter clutch (TCC). As engine warms, sensor resistance reduces. At normal operating temperature, voltage signal will be about .5-1.1 volts (4.3L Turbo) or 1.5-2.0 volts (all other models) at ECM coolant sensor signal terminal.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This tests if code was set because of a hard failure or intermittent condition. Code 14 sets if signal voltage indicates a coolant temperature greater than 275°F (135°C) for more than 3 seconds on 4.3L Turbo or 6 seconds on all other models.
2. This simulates conditions for a Code 15. If ECM recognizes open circuit by displaying a low temperature, ECM and wiring are not at fault.

After engine is started, temperature should rise steadily to about 194°F (90°C), then stabilize when thermostat opens. If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor (if equipped) should read close to each other, when measured with a scan tester.

CODE 14 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1) (2)

CODE 14, Schematic, Coolant Sensor Signal Voltage Low. Scheme 340

CODE 14, Flowchart, Coolant Sensor Signal Voltage Low. Scheme 341

CODE 15, COOLANT SENSOR SIGNAL VOLTAGE HIGH

As engine warms, sensor resistance reduces and voltage drops. At normal operating temperature, voltage signal will be about .5-1.1 volts (4.3L Turbo) or 1.5-2.0 volts (all other models) at ECM coolant sensor signal terminal. If sensor signal circuit opens, ECM will see -40°F (-40°C) and deliver fuel for this temperature.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This checks if code was set as a result of a hard failure or intermittent condition. Code 15 will set if engine is running for more 50 seconds and signal voltage indicates a coolant temperature less than -22°F (-30°C) for more than 30 seconds.
2. This simulates conditions for a Code 14. If ECM recognizes grounded circuit and displays a high temperature, ECM and wiring are okay.
3. This determines if problem is ECM or wiring. There should be 5 volts present at sensor when measured with a DVOM.

After engine starts, temperature should rise steadily to about 194°F (90°C) and stabilize when thermostat opens. If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor (if equipped) should read close to each other when measured with a scan tester. Code 15 will also set if sensor signal or ground circuit is open.

CODE 15 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1) (2)

CODE 15, Flowchart, Coolant Sensor Signal Voltage High. Scheme 342

CODE 16, TRANSMISSION OUTPUT SPEED - 5.0L & 5.7L WITH 4L60E TRANSMISSION

VSS signal buffer supplies 2002 pulses per mile to PCM on vehicle speed signal circuit. Code 16 will set if this signal is lost due to an open or grounded signal line.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This tests for battery voltage at VSS buffer.
2. This tests for proper ground path for VSS buffer.
3. This tests for VSS buffer signal to PCM.
4. This test checks for faulty connections and a faulty VSS buffer.

Check connections at VSS buffer and PCM. If other codes are set along with Code 16 refer to appropriate code chart for diagnosis and repair.

CODE 16, Schematic, Trans. Output Speed (5.0L & 5.7L W/ 4L60E Trans.). Scheme 343

CODE 16, Flowchart, Trans. Output Speed (5.0L & 5.7L W/ 4L60E Trans.). Scheme 344

CODE 21, TPS SIGNAL VOLTAGE HIGH

Throttle Position Sensor (TPS) provides a varying voltage signal depending on throttle valve angle. Signal voltage varies from about .50 volt at idle to 4.5 volts at wide open throttle. Each time TPS voltage drops to less than 1.25 volts and stops, ECM assumes this is zero degrees throttle angle and measures throttle percentage angle from this point.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test confirms Code 21 and checks if fault is a hard failure or an intermittent condition. Code 21 will set if TPS voltage is greater than 2.5 volts 2-10 seconds with engine running. On 2.8L, Code 21 may set if MAP sensor signal less than 2 volts.
2. This test simulates conditions for Code 22. If ECM recognizes low voltage signal and sets Code 22, ECM and power and signal circuits are not at fault.
3. This step isolates a faulty sensor, ECM or an open ground circuit.

A scan tester displays throttle position in volts. Closed throttle voltage should be less than 1.0 volt (4.3L Turbo) or less than 1.25 volts (all other models). TPS voltage should increase at a steady rate to about 4.5 volts as throttle angle increases. Code 21 will also result if ground circuit is open or TPS signal circuit is shorted to voltage.

CODE 21 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 21, Schematic, TPS Signal Voltage High. Scheme 345

CODE 21, Flowchart, TPS Signal Voltage High. Scheme 346

CODE 22, TPS SIGNAL VOLTAGE LOW

Throttle Position Sensor (TPS) provides a varying voltage signal depending on throttle valve angle. Signal voltage varies from less than about .50 volt at idle to 4.5 volts at wide open throttle.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test confirms Code 22 and tests if fault is a hard failure or an intermittent condition. Code 22 will set if engine is running and TPS voltage is less than .2 volt for 2-4 seconds.
2. This simulates Code 21. If ECM recognizes a high voltage signal and sets Code 21, ECM and wiring are not at fault. Replace TPS.
3. This simulates a high voltage signal to check for on open TPS signal circuit.

A scan tester displays throttle position in volts. Closed throttle voltage should be less than 1.0 volt (4.3L Turbo) or less than 1.25 volts (all other models). TPS voltage should increase at a steady rate to about 4.5 volts as throttle angle increases. Code 22 will also set if TPS signal or ground circuits are open or grounded.

CODE 22 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 22, Flowchart, TPS Signal Voltage Low. Scheme 347

DTC 24, VEHICLE SPEED SIGNAL LOW ("C" & "K" SERIES, M/T ONLY)

The ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 connects to Vehicle Speed Sensor (VSS) buffer, which alternately grounds circuit No. 437 when receiving voltage pulses from VSS (drive wheels are turning). The pulsing action occurs approximately 2000 times per mile and the ECM calculates vehicle speed based on the time between pulses. Scan tester reading should closely match speedometer reading with drive wheels turning.

Note. Test numbers refer to numbers on diagnostic chart.

1. DTC 24 will set after the following conditions are met for at least 40 seconds: circuit No. 437 voltage is constant, engine speed is more than 2000 RPM, and vehicle speed signal at ECM terminal A9 is less than 5 MPH.
2. This test determines if VSS buffer is receiving alternating current signal from vehicle speed sensor. Use Digital Volt-Ohmmeter (DVOM) on 20-volt AC scale.
3. This test monitors voltage on circuit No. 437. With wheels turning, the pulsating action causes a varying voltage. Voltage variation will be greater at low wheel speeds and an average of 4-6 volts at about 20 MPH.

With drive wheels turning, scan tester and speedometer reading should closely match.

Scheme 348

Scheme 349

DTC 24, VEHICLE SPEED SIGNAL LOW (WITH 4L60-E A/T)

The speed sensor circuit consists of a magnetic-induction sensor, Vehicle Speed Sensor (VSS) buffer, and wiring. Gear teeth on output shaft induce an alternating current in sensor. This signal is then transmitted to buffer. The buffer compensates for various axle ratios and converts signal into a square wave signal for use by the speedometer, cruise control ABS, and ECM.

The buffer sends 2 different signals to the ECM. circuit No. 437 relays transmission output speed, which is used to control shift points, line pressure torque converter clutch and DTC 24 and 72. Circuit No. 1716 relays vehicle speed which is used to control engine operating conditions and DTC 16. When DTC 24 sets, only 2nd gear at maximum line pressure will occur. DTC 24 sets when the following conditions are met for 6.4 seconds

1. Transmission is not in Park or Neutral.
2. Circuit No. 437 voltage is constant.
3. Engine speed is more than 3000 RPM.
4. Output speed less than 250 RPM.
5. Manifold absolute pressure 14.5-36.9 psi (100-255 kPa).
6. Throttle position 10-100 percent. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This test monitors voltage on circuit No. 437. With wheels turning, the pulsating action causes a varying voltage. Voltage variation will be greater at low wheel speeds and an average of 4-6 volts at about 20 MPH.
2. Less than one volt at ECM connector indicates circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS buffer. If voltage now reads more than 10 volts, the VSS buffer is faulty. If voltage remains less than 10 volts, then circuit No. 437 is grounded. If circuit No. 437 is not grounded, check for a faulty ECM connector or ECM.
3. A steady 8-12 volt reading at the ECM connector indicates that circuit No. 437 is open or VSS buffer is faulty.

Check all connections at transmission pass-through connector.

Scheme 350

Scheme 351

DTC 24, VEHICLE SPEED SIGNAL LOW (WITH 4L80-E A/T)

The PCM/TCM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 connects to Vehicle Speed Sensor (VSS) buffer, which alternately grounds circuit No. 437 when receiving voltage pulses from VSS (drive wheels are turning). The pulsing action occurs approximately 2000 times per mile and the ECM calculates vehicle speed based on the time between pulses. Scan tester reading should closely match speedometer reading with drive wheels turning. DTC 24 sets when the following conditions are met for 5 seconds

1. Transmission is not in Park or Neutral.
2. Circuit No. 437 voltage is constant.
3. Engine speed is more than 1200 RPM.
4. VSS signal indicates less than 2 MPH. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This test monitors voltage on circuit No. 437. With wheels turning, the pulsating action causes a varying voltage. Voltage variation will be greater at low wheel speeds and an average of 4-6 volts at about 20 MPH.
2. Less than one volt at PCM/TCM connector indicates circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS buffer. If voltage now reads more than 10 volts, the VSS buffer is faulty. If voltage remains less than 10 volts, then circuit No. 437 is grounded. If circuit No. 437 is not grounded, check for a faulty PCM/TCM connector or faulty PCM/TCM.
3. A steady 8-12 volt reading at the PCM/TCM connector indicates circuit No. 437 is open or VSS buffer is faulty.
4. This is normal voltage, which indicates a possible intermittent condition.

Check all connections at transmission pass-through connector.

Scheme 352

Scheme 353

CODE 31, ENGINE SPEED GOVERNOR - 5.7L "G" SERIES

The PCM controls the engine speed control governor based upon engine speed (RPM). The PCM sends a pulse width modulation signal to the engine speed control governor module to drive the engine speed control governor motor. Depending upon the amount of governing required, the module translates the PCM data into a voltage signal which it sends to the motor. The motor then pulls back the throttle to the correct overspeed condition.

A Code 31 will set if a fault occurs in the governor module, motor, linkage, wiring or PCM. If Code 31 is set, the PCM will limit engine speed by momentarily reducing fuel delivery to injectors.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Determines if engine speed governor module has proper voltage.
2. Applying voltage to the motor will determine motor, wiring and linkage integrity. DO NOT hold current to motor for longer than 30 seconds or damage to motor will result.
3. This will command full governing to determine if PCM or engine speed governor is at fault.

Before replacing PCM, use ohmmeter to check resistance of each PCM-controlled relay and solenoid. Replace any relay or solenoid where resistance is less than 20 ohms.

CODE 31, Schematic, Engine Speed Governor (5.7L "G" Series). Scheme 354

CODE 31, Flowchart, Engine Speed Governor (5.7L "G" Series). Scheme 355

CODE 32, EGR SYSTEM ERROR - 5.0L & 5.7L "G" SERIES

PCM controls a solenoid regulating vacuum to EGR valve. Normally closed solenoid prevents vacuum from passing until it is energized by PCM. A properly operating EGR will directly affect fuel integrator counts. With EGR valve open, integrator counts will be less than without EGR operation. If monitored integrator counts do not change with EGR commanded, Code 32 will set.

Note. Test numbers refer to test numbers on diagnostic chart.

1. When test terminal "B" of ALDL connector is grounded, EGR solenoid should be energized, allowing vacuum to EGR valve. Vacuum should hold.
2. When jumper wire is removed from terminal "B", vacuum to EGR valve should bleed through a vent in solenoid and EGR valve should close. Vacuum gauge may or may not bleed off vacuum. However, this does not indicate a problem.
3. Determines if fault lies in electrical control part of system, connector or solenoid.
4. This system uses a negative backpressure EGR valve. Valve should hold vacuum with engine off.
5. When engine is started, backpressure should cause vacuum to bleed off and valve should fully close.

Prior to replacing PCM, check resistance of all PCM-controlled solenoids and relays. Replace any with a resistance value less than 20 ohms.

CODE 32, Schematic, EGR System Error (5.0L & 5.7L "G" Series, Non-Cal. W/ 4L60E Trans). Scheme 356

CODE 32, Flowchart, EGR System Error (5.0L & 5.7L "G" Series). Scheme 357

CODE 32, EGR SYSTEM ERROR - 5.0L & 5.7L "C" & "K" SERIES CAL. WITH 4L60E TRANSMISSION & 5.7L & 7.4L "C", "G", "K" & "P" SERIES WITH 4L80-E TRANSMISSION

PCM controls a solenoid that regulates vacuum to EGR valve. The normally closed solenoid prevents vacuum from passing until it is energized by PCM. A properly operating EGR will directly affect fuel integrator counts. With EGR valve open, integrator counts will be less than without EGR operation. If monitored integrator counts do not change with EGR commanded, Code 32 will set.

ECM checks EGR operation when engine speed is greater than 1600 RPM, MAP sensor signal indicates cruise condition and throttle position are constant.

Note. Test numbers refer to test numbers on diagnostic chart.

1. With ignition on and engine off, solenoid should not be energized or allow vacuum to pass to EGR valve. When test terminal "B" of ALDL connector is grounded, EGR solenoid should be energized, allowing vacuum to EGR valve. Vacuum should hold.
2. Checks for plugged EGR passages. If passages are plugged, engine may have severe detonation on acceleration.
3. Vehicle must be driven during this test to produce sufficient load to operate EGR. Lightly accelerating (approximately 1/4 throttle) will produce a large and stable enough reading to determine if ECM is commanding system on.

Prior to replacing PCM, check resistance of all PCM-controlled solenoids and relays. Replace any with a resistance value less than 20 ohms.

CODE 32, Schematic, EGR Sys. Error (5.0L & 5.7L C & K Series Cal. W/ 4L60E Trans.). Scheme 358

CODE 32, Schematic, EGR Sys. Error (5.7L & 7.4L C,G,K & P Series W/ 4L80E Trans). Scheme 359

CODE 32, Flowchart, EGR Sys. Error (5.0L & 5.7L C & K Series W/ 4L60E Trans; 5.7L & 7.4L C,G,K & P Series W/ 4L80E Trans.). Scheme 360

CODE 32, EGR SYSTEM ERROR - 2.5L, 2.8L & 4.3L ("C", "K" & P SERIES), 4.3L "S" & "T" SERIES PICKUP (EXCEPT TURBO) 5.0L ("C" & "K" SERIES), 5.7L ("C", "K" & P SERIES) & 7.4L "C" & "K" SERIES; ALL WITH MANUAL TRANSMISSION

ECM controls a solenoid that regulates vacuum to EGR valve. The normally closed solenoid prevents vacuum from passing until it is energized by ECM. A properly operating EGR will directly affect fuel integrator counts. With EGR valve open, integrator counts will be less than without EGR operation. If monitored integrator counts do not change with EGR commanded, Code 32 will set.

ECM checks EGR operation when vehicle speed is greater than 50 MPH, engine vacuum indicates cruise and throttle position are steady.

Note. Test numbers refer to test numbers on diagnostic chart.

1. With ignition on and engine off, solenoid should not be energized or allow vacuum to pass to EGR valve. When test terminal "B" of ALDL connector is grounded, EGR solenoid should be energized, allowing vacuum to EGR valve. Vacuum should hold.
2. Checks for plugged EGR passages. If passages are plugged, engine may have severe detonation on acceleration.
3. SERVICE ENGINE SOON light should also flash while diagnostic terminal is grounded. If light does not flash, this may indicate Quad-Driver has been damaged by low TCC circuit resistance.
4. Vehicle must be driven during this test to produce sufficient load to operate EGR. Lightly accelerating (approximately 1/4 throttle) will produce a large and stable enough reading to determine if ECM is commanding system on.

Prior to replacing PCM, check resistance of all PCM-controlled solenoids and relays. Replace any solenoids or relays with a resistance value less than 20 ohms.

CODE 32, Schematic, EGR Sys. Error (5.0L & 5.7L C & K Series W/ M/T). Scheme 361

CODE 32, Schematic, EGR Sys. Error (5.7L P Series & 7.4L C & K Series W/ M/T). Scheme 362

CODE 32, Flowchart, EGR Sys. Error (5.0L & 5.7L C & K Series; 5.7L P Series; 7.4L C & K Series; All W/ M/T). Scheme 363

CODE 33, MAP SENSOR SIGNAL VOLTAGE HIGH

Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). If MAP sensor fails, ECM will substitute a fixed MAP value and use TPS input to control fuel delivery.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test confirms Code 33 and determines if it is a hard failure or an intermittent condition. Code 33 will set when voltage signal reading is too high and TPS voltage indicates throttle is closed.
2. This step simulates conditions for a Code 34. If ECM recognizes and indicates low MAP signal, ECM and 5-volt reference and MAP signal circuits are not at fault.

With ignition switch in ON position and engine off, manifold pressure is equal to atmospheric pressure and signal voltage is high. Comparing BARO readings from a known good vehicle using the same sensor is a good way to check accuracy of suspected sensor. Readings should be within .4 volt of each other. Code 33 will also result if ground circuit is open or MAP signal circuit is shorted to voltage or to 5-volt reference circuit.

CODE 33 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 33, Schematic, MAP Sensor Voltage High. Scheme 364

CODE 33, Flowchart, MAP Sensor Voltage High. Scheme 365

CODE 34, MAP SENSOR SIGNAL VOLTAGE LOW

Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). If MAP sensor fails, ECM will substitute a fixed MAP value and use TPS input to control fuel delivery.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This confirms Code 34 and determines if code was a hard failure or an intermittent condition. Code 34 will set when ignition is on and MAP signal voltage is low. On some systems, engine must be running to set code.
2. Jumpering harness 5-volt reference circuit and MAP signal circuit terminals will determine if problem is sensor, ECM or wiring. If ECM recognizes and indicates high MAP signal, ECM and wiring are okay.
3. Scan tester may not display 12 volts. The important thing is that the ECM recognizes voltage as greater than 4 volts (high MAP voltage signal), indicating ECM and MAP signal circuit are not at fault.

With ignition switch in ON position and engine off, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparing BARO readings with a known good vehicle using the same sensor is a good way to check accuracy of suspected sensor. Readings should be within .4 volt of each other. A Code 34 will also result if 5-volt reference and MAP signal circuits are open or shorted to ground. If 5-volt reference circuit is not shorted to ground and a Code 22 is stored, check MAP signal circuit for short to ground.

CODE 34 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 34, Flowchart, MAP Sensor Signal Voltage Low. Scheme 366

CODE 35, IDLE SPEED ERROR

Code 35 will set when closed throttle engine speed is 150 RPM greater or less than correct idle speed for 20 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. IAC driver is used to extend and retract IAC valve. Movement is verified by changing engine speed. If no engine speed change occurs, valve can be retested when removed from throttle body.
2. Checks IAC movement quality from step 1). Between 700-1500 RPM, engine speed should change smoothly with each tester light flash while extending or retracting. If IAC valve is retracted beyond control range (about 1500 RPM), it may take many flashes in extend position before engine speed reduces. This is normal on some engines. Fully extending IAC may cause engine to stall. This may be normal.
3. Steps 1) and 2) verified proper IAC valve operation. This step checks IAC circuits. Each light on node light should flash Red and Green, while IAC valve is cycled. While color sequence is not important, if either light is off or does not flash Red and Green, check circuits beginning with poor terminal contacts.

IAC VALVE RESET PROCEDURE

Turn ignition off for 10 seconds. Start and run engine for 5 seconds. Turn ignition off another 10 seconds.

A slow, unstable idle may be caused by a system problem that cannot be overcome by IAC. Scan counts will be greater than 60 if too low, and zero counts if too high. If idle is too high, stop engine. With ignition on, ground ALDL test terminal "B". Wait 45 seconds for IAC to seat, then disconnect IAC. Start engine. If idle speed is greater than 800 RPM, inspect vehicle for vacuum leaks.

System Too Lean

If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary and disconnecting IAC may not help. Scan tester and/or digital voltmeter (10 megohm) will read an oxygen sensor output less than 300 mv (.3 volt). Check for low fuel pressure or water in fuel.

System Too Rich

If air/fuel ratio is too rich, idle speed will be too low and scan tester counts will usually be greater than 80. The system may be obviously rich with Black smoke from tailpipe. Scan tester and/or voltmeter will read an oxygen sensor voltage signal fixed greater than 800 mv (.8 volt). Look for high fuel pressure or leaking/sticky injectors. Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging bore. A silicone-contaminated oxygen sensor will produce lean air/fuel mixture. Oxygen sensor output would be fixed greater than 800 mv (.8 volt). This may also set Code 45.

Throttle Body

Remove IAC and inspect bore for evidence of IAC valve dragging.

IAC Valve Connections

Carefully inspect connections for looseness or corrosion.

PCV Valve

The wrong PCV valve may cause incorrect idle speed.

CODE 35 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 35, Schematic, Idle Speed Error. Scheme 367

CODE 35, Flowchart, Idle Speed Error. Scheme 368

CODE 42, ELECTRONIC SPARK TIMING

Code 42 indicates ECM has seen an open or short to ground in High Energy Ignition Electronic Spark Timing (HEI EST) system or by-pass circuits.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test confirms Code 42 and determines if fault is a hard failure or intermittent condition.
2. This tests for a normal EST ground path through ignition module. If circuit No. 423 is shorted to ground, reading will be less than 500 ohms.
3. As test light voltage touches circuit No. 424, module should switch. This causes ohmmeter to "over-range" with meter in 100-200 ohm range. A higher ohm range will indicate over 5000 ohms. This test assures module switched.
4. If module did not switch, this step tests for a short in circuit No. 423, an open in circuit No. 424 and a faulty ignition module connection or module.
5. This step confirms Code 42 is a faulty ECM and not an intermittent problem in circuits No. 423 and 424.

The scan tester cannot help diagnose a Code 42 problem. See INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 42, Schematic, Elec. Spark Timing (V8 C, K & P Series W/ M/T). Scheme 369

CODE 42, Schematic, Elec. Spark Timing (All Models W/ 4L60E Trans. Exc. CPI). Scheme 370

CODE 42, Schematic, Elec. Spark Timing (All W/ 4L60E Trans. & CPI). Scheme 371

CODE 42, Schematic, Elec. Spark Timing (All W/ 4L80E Trans.). Scheme 372

CODE 42, Flowchart, Elec. Spark Timing. Scheme 373

CODE 43, ELECTRONIC SPARK CONTROL WITH SPARK CONTROL MODULE

Note. Test numbers refer to test numbers on diagnostic chart.

1. If conditions for a Code 43 exist, scan tester will display YES. A knock signal should exist at idle unless an internal or system problem exists.
2. Determines if system is functioning. Usually, a knock signal can be made by tapping on exhaust manifold. If knock signal is not made, try tapping on engine block near sensor. On models with automatic transmission, it may be necessary to place gear selector lever in Drive.
3. Because Code 43 sets when signal voltage on spark retard line remains low, this test should cause signal on that line to go high. The 12-volt signal should be seen by ECM as a "no knock" signal if ECM and wiring are okay.
4. This test determines if knock signal is detected on sensor-to-controller line or if ESC module is at fault.
5. If sensor line is routed too close to secondary ignition wires, ESC module may see interference as a knock signal.
6. This checks ground circuit to module. An open ground will cause voltage on monitored line to remain constant at about 12 volts. This would cause Code 43 functional test to fail.
7. This should generate a knock signal to controller. This determines if ESC controller is operating correctly.

Code 43 can be caused by a faulty knock sensor connection at ESC module or ECM. Also, check controller-to-ECM signal line for an open or short to ground.

CODE 43 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 43, Schematic, ESC W/ Spark Control Module. Scheme 374

CODE 43, Flowchart, ESC W/ Spark Control Module. Scheme 375

CODE 43, ELECTRONIC SPARK CONTROL WITHOUT ESC MODULE (SINGLE SENSOR)

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 43 will set when vehicle reaches normal operating temperature (but not overheating), high engine load is indicated by MAP sensor and voltage on circuit No. 496 is greater than 3.5 volts DC or less than 1.5 volts DC. This step determines if system is functioning properly at current time.
2. This step determines state of 5-volt reference signal applied to sensor.
3. Checks knock sensor internal resistance.

ECM/PCM applies and monitors a 5-volt DC signal to knock sensor. Internal knock sensor circuitry pulls this DC signal down to about 2.5 volts. When knock sensor detects detonation, it generates an AC signal which rides back on DC signal to ECM/PCM. Knock signal intensity is dependent upon knock signal level.

CODE 43, Schematic, ESC W/O Spark Control Module. Scheme 376

CODE 43, Flowchart, ESC W/O Spark Control Module. Scheme 377

CODE 44, LEAN EXHAUST INDICATION

Sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 44 sets when O2 sensor signal remains low for a precalibrated period and system is operating in "closed loop".

Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If Code 44 conditions exist, block learn value will be around 150-172.

O2 Sensor Wire

Wire may be mispositioned and touching exhaust manifold. Check for ground between sensor and wire connector.

Fuel Contamination

Water, even small amounts, near in-tank fuel pump inlet can reach fuel injector, causing a lean exhaust and setting Code 44.

Fuel Pressure

System will be lean if fuel pressure is low. It may be necessary to monitor fuel pressure while driving vehicle. For fuel pressure checking procedure, see BASIC TESTING article in this section.

Exhaust Leaks

If exhaust system has large leaks, exhaust system negative pressure pulses can cause outside air to be drawn into system and past O2 sensor. Vacuum or crankcase leaks can also cause a lean condition. If Code 44 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 44 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 44, Flowchart, Lean Exhaust Indication. Scheme 378

CODE 45, RICH EXHAUST INDICATION

Sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation. Code 45 indicates a rich exhaust and diagnosis should begin with: fuel pressure, leaking injector, HEI shielding, canister purge saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Tests if O2 sensor is registering a rich condition. Code 45 is set when vehicle is at operating temperature (in "closed loop"), throttle angle is greater than 5 percent, O2 sensor signal at ECM is greater than .75 volt for 60 seconds or more.

Code 45, rich exhaust, is most likely caused by one of the following

Fuel Pressure High

If fuel pressure is too high, air/fuel ratio will be rich. For fuel pressure checking procedure, see BASIC TESTING article in this section. The ECM can compensate for slight increases but if air/fuel ratio becomes too rich a Code 45 will be set.

Ignition Ground

If an open occurs at circuit No. 453, HEI induced electrical "noise" may result, causing simulated reference pulses picked up by ECM on EST harness reference line. Additional pulses result in a higher than actual engine speed signal. The ECM will increase injector pulse width ("on" time) to match increased RPM signal. Scan tester will show higher than actual RPM, which can help diagnose problem.

Fuel Canister

Charcoal canister fuel saturation will cause a rich air/fuel ratio. If full of fuel, check canister control and hoses.

MAP Sensor

If ECM senses higher than normal manifold pressure (low vacuum) system can go rich. Disconnecting MAP sensor allows ECM to substitute a fixed value for the MAP sensor. If rich condition disappears, replace MAP sensor and continue testing.

TPS

An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.

O2 Sensor Contamination

O2 sensor contamination, caused by silicone in certain fuels or use of improper RTV sealant, may cause a White-powdery coating to cover O2 sensor. The false high signal voltage produced (or low oxygen content sensed) is interpreted by ECM as a rich mixture, causing ECM to set Code 45.

EGR Problem

EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling. If Code 45 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 45 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 45, Flowchart, Rich Exhaust Indication. Scheme 379

CODE 51, FAULTY PROM/MEM-CAL

Ensure all pins are fully inserted in socket. If okay, replace PROM/MEM-CAL, clear memory and recheck. If Code 51 reappears, replace ECM.

CODE 52, FAULTY CALPAK

Ensure all pins are fully inserted in socket. If okay, replace CALPAK, clear memory and recheck. If Code 51 reappears, replace ECM.

CODE 53, SYSTEM OVERVOLTAGE

This code indicates a basic charging system problem. Code 53 will set when voltage at ECM terminal is greater than 17.1 volts for 2 seconds. Check and repair charging system.

CODE 55, ECM/PCM ERROR

Ensure ECM grounds are good and MEM-CAL is properly latched. If okay, replace ECM/PCM. Clear codes and confirm closed loop operation. Check operation of SERVICE ENGINE SOON light.

CODE 54, FUEL PUMP CIRCUIT

Code 54 will set if ECM does not see 12 volts on fuel pump signal voltage monitor during the first 2 seconds after ignition is turned on.

CODE 54, Schematic, Fuel Pump Cir. (5.7L C,K & P Series; 5.0L & 7.4L C & K Series; All W/ M/T). Scheme 380

CODE 54, Schematic, Fuel Pump Cir. (5.0L & 5.7L C & K Series W/ 4L60E Trans.). Scheme 381

CODE 54, Schematic, Fuel Pump Cir.(5.0L & 5.7L G Series W/ 4L60E Trans.). Scheme 382

CODE 54, Schematic, Fuel Pump Cir.(All Models W/ 4L80E Trans). Scheme 383

CODE 54, Flowchart, Fuel Pump Circuit. Scheme 384

See also:
• READING TROUBLE CODES
• RETRIEVING CODES (NON-SCAN)
• HARD OR INTERMITTENT TROUBLE CODE DETERMINATION
• TROUBLE CODE IDENTIFICATION
• SCAN TESTER DATA
• SCAN TESTER USAGE
• CLEARING TROUBLE CODES
• DIAGNOSTIC PROCEDURE