Engine Controls - Tests W/codes - 1.9l Tbi Saturn SL I

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 BASIC TESTING article in this section. Failure to do so may result in lost diagnostic time.

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed with DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. 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.

SELF-DIAGNOSTIC SYSTEM

Note. Electronic Control Module (ECM) may also be referred to as Powertrain Control Module (PCM) in some diagnostic charts and figures. Terms are used interchangeably.

Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will illuminate SERVICE ENGINE SOON light located on instrument panel. When malfunction is detected and light is turned on, a corresponding trouble code will be stored in control module memory. To retrieve stored codes, see RETRIEVING CODES (NON-SCAN). Malfunctions are recorded as hard failures or as intermittent failures.

In addition to hard failures and intermittent failures, Saturn models also store information flags and codes in malfunction history. Information flags indicate a failure and will not turn on SERVICE ENGINE SOON light. Information flags and codes stored in malfunction history are used as a diagnostic tool to help technician when hard codes or intermittent problems occur.

Hard Failures

Hard failures cause SERVICE ENGINE SOON light to glow and remain on until malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, control module will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but it will most likely encounter degraded driveability.

Intermittent Failures

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

Malfunction History & Information Flags

Engine information flags will not cause SERVICE ENGINE SOON light to glow. Unlike hard failures and intermittent failures, information flags and codes stored in malfunction history will not be erased from PCM memory after 50 engine restarts. Flags and codes stored in malfunction history can only be retrieved and cleared from PCM memory using a "Scan" tester.

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. DIAGNOSTIC CIRCUIT CHECK must be performed before using trouble code charts. See «BASIC TESTING»(/saturn/sl/i-1990-1995/remont/testing-diagnostics/#engine-controls-basic-testing) article in this section.
2. If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent trouble codes. Hard codes will cause SERVICE ENGINE SOON light to glow continuously while engine is running. See 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»(/saturn/sl/i-1990-1995/remont/testing-diagnostics/#engine-controls-tests-wo-codes) article in this section. Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes.
3. If no trouble codes were displayed and a driveability problem exists, refer to SYMPTOMS in «TESTS W/O CODES»(/saturn/sl/i-1990-1995/remont/testing-diagnostics/#engine-controls-tests-wo-codes) article in this section. Doing so will identify proper system or component to check in appropriate I - SYS/COMP TESTS article in this section.
4. After repairs are made, clear any trouble codes and perform FIELD SERVICE MODE CHECK in «BASIC TESTING»(/saturn/sl/i-1990-1995/remont/testing-diagnostics/#engine-controls-basic-testing) article in this section. NOTE: For information on retrieving codes using a "Scan" tester, refer to user and reference manuals supplied with tester. NOTE: Inserting jumper wire into test and ground terminals of ALDL connector with engine running will cause fuel injected vehicles to enter field service mode. Flashes of SERVICE ENGINE SOON light will not indicate codes if this is done. See FIELD SERVICE MODE CHECK in «BASIC TESTING»(/saturn/sl/i-1990-1995/remont/testing-diagnostics/#engine-controls-basic-testing) article in this section.
5. Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate Assembly Line Data Link (ALDL) connector attached to control module wiring harness. Most ALDL connectors are located under dash on driver side of vehicle. For exact location of ALDL, see COMPONENT LOCATIONS in appropriate I - SYS/COMP TESTS article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of ALDL connector. (Scheme 48)
6. SERVICE ENGINE SOON light should begin to flash codes. Each code will be repeated 3 times. If codes are not flashed or SERVICE ENGINE SOON light does not glow, perform DIAGNOSTIC CIRCUIT CHECK in «BASIC TESTING»(/saturn/sl/i-1990-1995/remont/testing-diagnostics/#engine-controls-basic-testing) article in this section. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.

Scheme 48

READING TROUBLE CODES

Note. On Saturn, only general information (hard and intermittent) codes may be retrieved using non-scan method. Malfunction history information flags and codes can be retrieved only by using a "Scan" tester.

Control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of SERVICE ENGINE SOON light or by reading digital display on a "Scan" tester. "Scan" tester is faster to use, more accurate and capable of reading information which otherwise would necessitate testing individual control module and sensor/solenoid connector terminals using a digital voltmeter. See SCAN TESTER USAGE and SCAN DATA.

Note. When using most "Scan" testers, a time delay exists between serial data updates. For instantaneous response, a digital voltmeter must be used.

If "Scan" tester is not available, reading flashes of SERVICE ENGINE SOON light is possible by grounding diagnostic test terminal "B" of ALDL with ignition on and engine off. For example, "FLASH, FLASH, pause, FLASH, longer pause" identifies Code 21. First series of flashes is first digit of trouble code. Second series of flashes is second digit of trouble code. Trouble codes are displayed starting with lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL test terminal is grounded.

Note. Trouble codes 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 codes may not set in a service bay operational mode and may require road testing vehicle in order to duplicate condition under which code will set.

TROUBLE CODE DEFINITION

ECM/PCM TROUBLE CODE DEFINITION

Note. Use trouble code charts only if SERVICE ENGINE SOON light 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 control module-related Codes 51, 52 or 55 are displayed with another code, start with 50-series code, and then proceed to lower numbered codes.

INFORMATION FLAG

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, determine if codes are hard failure codes or intermittent failure codes. Diagnostic charts will not usually help analyze intermittent codes. To determine hard codes and intermittent codes

1. Manually enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See CLEARING TROUBLE CODES.
2. Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. SERVICE ENGINE SOON light should go out. Run warm engine at specified curb idle for 2 minutes and note SERVICE ENGINE SOON light.
3. If SERVICE ENGINE SOON light comes on, manually enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Codes 13, 15, 24, 44 and 45 may require a road test to reset hard failure after trouble codes were cleared.
4. If SERVICE ENGINE SOON light does not come on, all stored trouble codes were intermittent failures, except as noted above.

CLEARING TROUBLE CODES

To clear general information codes, turn ignition switch to ON position and jumper diagnostic test terminal "B" to ground terminal "A" at ALDL connector 3 times within 5 seconds. General information codes will also clear automatically if they do not reoccur within 50 ignition "on" cycles. Malfunction history codes and information flags can only be cleared using a "Scan" tester.

INFORMATION FLAGS

Note. Use information flags for diagnostic purposes only. Flags do not necessarily indicate component failure or malfunction.

Flag 16: Electrical Variable Orifice (EVO) Fault

EVO valve is controlled and monitored by PCM. When vehicle speed is zero MPH, current from PCM will be zero milliamps. Once vehicle speed reaches 12 MPH, current will gradually increase from 120 milliamps to 650 milliamps as vehicle speed increases from 12 to 55 MPH.

Flag 16 may set due to loss of ignition while vehicle is moving. When monitoring EVO output and feedback on a "Scan" tester, readings will have an inverse ratio. When output is 100 percent, feedback will be zero percent. Feedback should increase with increase in vehicle speed. If output decreases and feedback increases proportionally, EVO subsystem is okay. Ensure resistance across EVO terminals is8-12 ohms, with no continuity to ground.

Flag 48: Reference Input Intermittent Or Noisy

Flag will set if PCM detects missing or extra reference pulses or if time between reference pulses is too long or to short. Using Malfunction History mode on "Scan" tester may help determine cause for setting of flag. Check for large RPM increase on start-up. Check for possible induced reference signal due to proximity of reference wire of harness to high electrical output wiring.

Flag 52: Battery Voltage Out Of Range

Flag sets if monitored battery voltage drops to less than 11 volts or increases to greater than 17 volts. Flag 52 can set if all accessories are on for extended idling periods; this does not indicate a problem.

Flag 53: ESC (Knock Present)

Flag will set if PCM cannot reduce engine knock by retarding timing. Mechanical engine knocks can result in setting of this flag. Check for valve lifter noise, loose belt tensioner or loose brackets. If no problems are found, try improving fuel quality and checking cooling system for proper operation.

Flag 54: 5-Volt Reference Ground

Flag will set if MAP sensor signal is zero volts, handwheel sensor (in steering wheel) signal is zero volts (if equipped) and TPS signal is zero volts. With ignition switch in OFF position, disconnect PCM harness connector. Check resistance to ground on harness terminals J2B05, J2B06 and J2A06. If resistance is less than 200 ohms, repair short to ground in faulty circuit. If resistance is not less than 200 ohms, check PCM harness connector terminal tightness. If harness connector terminals are okay and scan indicates low voltage on all 3 circuits, replace PCM.

Flag 58: Battery Voltage Unstable

Flag will set if battery voltage changes more than 3 volts instantaneously. See INTERMITTENTS in TESTS W/O CODES article in this section.

Flag 61: 6X Signal Fault (1991)

Flag will set if 6X pulses do not occur between each reference pulse or a 6X pulse does not immediately follow a reference pulse. Flag could set due to opens or intermittents in DIS module harness.

Flag 63: Option Check Sum Error

Each time PCM is powered up, a comparison of tire size options is performed. Tire size and options must compare to valid combination options stored in EEPROM.

Flag 67: Handwheel Sensor Circuit Fault

Flag will set if vehicle speed is 5-30 MPH and handwheel sensor voltage is less than .2 volt or greater than 4.8 volts. Handwheel sensor is located at base of steering column, 5" from bulkhead. If Flag 67 is set with Flag 54, diagnose Flag 54 first. Flag may set if drive wheels are operated with vehicle on hoist.

Flag 71: Cooling System High Temperature

Flag will set if engine coolant temperature is greater than 239°F (118°C). Check for low coolant, faulty thermostat (stuck closed), reservoir cap damage, collapsed radiator hoses, faulty water pump and plugged radiator. Towing a trailer on a grade or extended high ambient idling may set this flag without presence of a problem.

Flag 72: Cooling System Low Temperature

Flag will set if coolant temperature is less than 32°F (0°C) after engine has been running 5 minutes. Flag indicates a lower than normal coolant temperature and does not indicate a faulty CTS. Check for faulty thermostat (stuck open) and a constantly running cooling fan.

Flag 73: Coolant Sensor Signal Unstable

Flag will set if Coolant Temperature Sensor (CTS) indicates a change of more than 59°F (15°C) instantaneously. See INTERMITTENTS in TESTS W/O CODES article in this section.

Flag 74: Coolant/Transmission Temperature Sensor Ratio Error

Flag will set if Transmission Temperature Sensor (TTS) is functioning and CTS reading is less than TTS reading. Flag indicates a degrading CTS. CTS resistance should be 2746-2826 ohms at 77°F (25°C). Check CTS for external contamination.

Flag 75: Air Temperature Sensor Signal Unstable

Flag will set if Air Temperature Sensor (ATS) indicates a temperature change of more than 59°F (15°C) instantaneously. See INTERMITTENTS in TESTS W/O CODES article in this section.

Flag 76: Throttle Position Sensor-To-MAP Sensor Voltage Out

Of Range

Flag will set if TPS voltage and MAP voltage readings do not correspond to internal relational tables built into EEPROM. Tables are built on normal engine operation. Check for corroded connections. Flag indicates either TPS or MAP sensor is out of calibration.

ECM/PCM LOCATION

On most models, engine control module is located behind right or left side of dash or behind right or left kick panel. See COMPONENT LOCATIONS in appropriate I - SYS/COMP TESTS article in this section.

Diagnostic Aids

Diagnostic aids (located in many trouble code charts) 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.

Field Service Mode Check

If ALDL test terminal "B" is grounded with engine running, SERVICE ENGINE SOON light will indicate operational mode of engine. This test confirms proper operation of fuel system 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 DIAGNOSTIC PROCEDURES article.

SPECIAL TOOLS (DIAGNOSTIC)

Note. A "Scan" tester plugged into ALDL may be used to read trouble codes and check voltages in system on serial data line (terminal "E", or terminal "M" on P-4 systems). This can save a great deal of time. For additional information, see SCAN TESTER USAGE and SCAN DATA.

Computerized engine control system is most easily diagnosed using "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 (for both TBI and PFI) 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 chart.

SCAN TESTER USAGE

Note. Before connecting "Scan" tester 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 DIAGNOSTIC CIRCUIT CHECK located in BASIC TESTING article in this section. If vehicle does not pass diagnostic circuit check, information received may be invalid.

"Scan" tester is a specialized tester which, when plugged into ALDL, 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" tester 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 control module; they do not indicate whether devices have responded properly to signal. Verify proper response at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine not running, but it may not be indicated by all makes of "Scan" testers.

A problem may exist even if trouble codes are not present. About 80 percent of driveability problems occur without trouble codes. Sensors that are out of specification will not set a trouble code but will cause driveability problems.

Using "Scan" tester is 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 DATA.

Note. 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, remove tester, turn ignition on and ground ALDL test terminal "B". Same codes flashed by SERVICE ENGINE SOON light should be indicated by "Scan" tester.

SCAN DATA

Note. Information contained in following tables is typical of readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are more frequent. Not all devices and systems are used on all models; following lists only represent most commonly used parameters. For additional information, refer to owner's manual furnished with tester.

THROTTLE BODY INJECTION

PCM/BCM CODE CHARTS

Note. In following diagnostic flow charts, schematics and illustrations are courtesy of General Motors Corp.

CODE 11: TRANSAXLE CODES PRESENT

The powertrain control module, used on vehicles equipped w/automatic transaxles, contains an engine control module (EC) and a transaxle control module (TC). These control modules communicate internally over a serial peripheral interface (SPI) bus. When the transaxle control module (TC) detects a malfunction in the automatic transaxle, a code is stored in the transaxle control module's memory and an indication is sent to the engine control module to turn on the malfunction indicator lamp. If the DLC is grounded, the transaxle codes flash on the SHIFT TO D2 telltale.

Code Parameter

Code 11 will set if the PCM/TC has set a transaxle code.

Search the scan tool for stored transaxle codes. Select TCM trouble codes.

When the PCM/TC codes are cleared, code 11 will also be cleared from general information but not from Malf history. Code 11 will not set if transaxle flags are present.

Diagnostic Check Only (Flash Code)

The PCM will flash Code 12 on the malfunction indicator lamp when it is able to perform diagnostics. The DLC must be grounded w/the key ON to flash codes.

Code Parameters

If diagnostics in the PCM are functioning, when the DLC is grounded Code 12 will flash on the malfunction indicator lamp.

Code 12 is a flash code. It is not shown on the Scan Tool.

CODE 13: OPEN OXYGEN (O2) SENS CKT

CODE 13 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This tests if problem still exists. Vehicle cannot enter "closed loop" mode if O2 sensor circuit is open. Code 13 indicates an open in O2 sensor circuit. Code will set if: Engine is at normal operating temperature. Neither Code 21 nor Code 22 is stored. O2 sensor voltage is constant within a specified range (.34-.55 volt). Throttle angle is greater than idle. A precalibrated amount of time has elapsed since start-up. All conditions have existed for a precalibrated amount of time.
2. Determines if O2 sensor, wiring or control module is at fault. If wiring is good, grounding O2 sensor wire will cause .45 volt reference supplied by control module to pull low.
3. This tests O2 sensor circuit wiring. Use only a high impedance (10-megohm minimum) digital voltmeter.

Control module will not go into closed loop if Code 13 is set. Code 13 may set if vehicle runs out of fuel or stalls while vehicle is in motion. If O2 sensor ground becomes loose, a false O2 sensor reading will occur. This can result in a Code 13 being set.

Scheme 49

Code 13, Flow Chart, Open Oxygen (O2) Sensor Ckt. Scheme 50

CODE 14: COOLANT TEMP SENS, SIGNAL VOLTAGE LOW

CODE 14 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.

1. Code 14 indicates control module has seen low coolant sensor voltage signal (high temperature) at control module terminal for a precalibrated period of time. This checks if conditions for Code 14 still exist.
2. This tests for grounded sensor signal line between control module and coolant sensor.

After engine is started, temperature should rise steadily to about 190°F (88°C) and then stabilize when thermostat opens. At normal operating temperature, signal voltage at control module terminal should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When Code 14 is set, control module will turn on electric cooling fan(s) if equipped.

Scheme 51

Code 14, Flow Chart, Coolant Temp Sens, Signal Voltage Low. Scheme 52

CODE 14 TEMPERATURE-TO-RESISTANCE VALUES (1)

CODE 15: COOLANT TEMP SENS, SIGNAL VOLTAGE HIGH

CODE 15 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 15 indicates control module has seen high resistance in coolant sensor circuit. This could be due to high resistance (cold temperature) or high voltage at coolant sensor terminal at control module for a precalibrated period of time. This checks if conditions for Code 15 still exist.
2. This test simulates a low voltage condition. If control module recognizes low voltage signal, "Scan" tester will display greater than 130°C. This indicates control module and wiring are not at fault.
3. This test determines if coolant sensor ground or signal circuit is open.

After engine is started, temperature should rise steadily to about 190°F (88°C) and then stabilize when thermostat opens. At normal operating temperature, voltage at control module sensor signal line should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When Code 14 is set, control module will turn on electric cooling fan(s) if equipped.

CODE 15 TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 15, Flow Chart, Coolant Temp Sens, Signal Voltage High. Scheme 53

CODE 17: PCM FAULT (PULL-UP RESISTOR)

PCM uses a coolant sensor signal pull-up resistor to increase sensing accuracy throughout entire range of operating temperatures. When coolant temperature is less than 104°F (40°C), a 4-k/ohm resistor is used. When temperature is greater than 104°F (40°C), PCM switches to a 348-ohm resistor. If pull-up resistor does not switch, Code 17 will set. Code 17 is an internal PCM fault; PCM must be replaced.

CODE 19: 6X SIGNAL FAULT

6X output signal is a 5-volt square wave that is initially high. Signal switches low at each of six 60-degree crankshaft position sensor pulses. 6X signal is used by PCM for greater resolution when determining ESC retard values. Code 19 will set if three 6X pulses do not occur between each reference pulse or a 6X pulse does not immediately follow a reference pulse.

Checking malfunction history on "Scan" tester may help determine cause of intermittent code. Check tightness of all terminals and connectors.

Code 19, Schematic, 6X Signal Fault. Scheme 54

Code 19, Flow Chart, 6X Signal Fault. Scheme 55

CODE 21: THROTTLE POSITION SENS, SIGNAL VOLTAGE HIGH

CODE 21 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent condition.
2. This test simulates a low-voltage condition. If control module recognizes change of state, control module and wiring are okay.
3. This step isolates a faulty sensor, control module or open sensor ground circuit. If sensor ground is shared by another sensor, an accompanying code related to that sensor may exist.

A "Scan" tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Code 21, Schematic, Throttle Position Sens Signal Voltage High. Scheme 56

Code 21, Flow Chart, Throttle Position Sens Signal Voltage High. Scheme 57

CODE 22: THROTTLE POSITION SENS, SIGNAL VOLTAGE LOW

CODE 22 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent condition.
2. This test simulates conditions for a Code 21. If control module recognizes change of state, control module and wiring are okay.
3. This simulates a high signal voltage to check for an open in TPS signal line to control module. "Scan" tester should recognize this signal and display high TPS voltage.

A "Scan" tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Code 22, Flow Chart, Throttle Position Sens, Signal Voltage Low. Scheme 58

CODE 23: MAT SENS SIGNAL VOLTAGE HIGH

CODE 23 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks if code is result of a hard failure or an intermittent condition. Code 23 will set if engine has been running for a precalibrated period of time, has reached operating temperature and signal voltage indicates a MAT temperature less than -22°F (-30°C).
2. This simulates conditions for a Code 25. If "Scan" tester displays a high temperature, control module and wiring are not at fault.
3. This checks for continuity of sensor signal and ground circuits. If ground circuit is shared by other sensors and ground circuit is open, accompanying codes related to those sensors may be present.

If engine is allowed to cool overnight, coolant and MAT sensor values should be close to each other when measured by "Scan" tester. Code 23 will result if signal and ground circuits become open. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.

CODE 23 TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 23, Schematic, MAT Sensor Signal Voltage High. Scheme 59

Code 23, Flow Chart, MAT Sensor Signal Voltage High. Scheme 60

CODE 24: VEHICLE SPEED SENS (VSS)

Code 24 will set if VSS indicates less than one MPH when engine speed is greater than normal idle RPM, MAP voltage is less than .5 volt and transaxle is not in Park or Neutral. Speed sensor is mounted on differential area of transaxle converter housing. PM generator speed sensor resistance is 700-900 ohms.

Code 24, Schematic, Vehicle Speed Sensor (VSS). Scheme 61

Code 24, Flow Chart, Vehicle Speed Sensor (VSS). Scheme 62

CODE 25: MAT SENS SIGNAL VOLTAGE LOW

CODE 25 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks if code is hard failure or intermittent condition. Code 25 will set if a MAT temperature greater than 266°F (130°C) is sensed for more than a precalibrated period.
2. This simulates condition for Code 23. If control module recognizes open circuit and "Scan" tester displays temperature of less than -30°C, control module and wiring are okay.

If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor values should be close to each other when measured by a "Scan" tester. A Code 25 will result if sensor signal circuit is shorted to ground. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.

CODE 25 TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 25, Flow Chart, MAT Sens Signal Voltage Low. Scheme 63

CODE 26: QUAD-DRIVER CKT

Code 26 will set if an open or short exists in any QDM output circuit. A comparison of driver input and output states is performed. If input and output are in same state (both high or both low), a fault is indicated and a Code 26 will set.

A shorted or open solenoid, relay or bulb can cause a Code 26. If only one output circuit is bad, PCM will shut down only that circuit and not entire quad-driver. If any corresponding codes exist (i.e., Code 32, EGR), diagnose that quad-driver first.

Component Resistances

1. EGR Solenoid; 28.8-35.2 ohms.
2. Canister Purge Solenoid; 28.8-35.2 ohms.
3. Coolant Fan Relay; 72-88 ohms.
4. A/C Relay; 72-88 ohms.

Code 26, Schematic, Quad-Driver Ckt. Scheme 64

Code 26, Flow Chart, Quad-Driver Ckt. Scheme 65

CODE 32: EGR SYS ERROR

If Code 26 is set with Code 32, diagnose Code 26 first and then clear codes and road test vehicle. If code reoccurs, use Code 32 chart to diagnose problem.

PCM verifies EGR function during a steady off-idle cruise (greater than 15 MPH) by grounding EGR drive circuit to energize solenoid and block off EGR vacuum source. This should result in a change in fuel control integrator. If a change is not seen by PCM, Code 32 is set.

Note. Test numbers refer to numbers on diagnostic chart.

1. With ignition off, EGR solenoid should be open. Vacuum should pass through EGR solenoid and open EGR valve.
2. With ignition on and ALDL test terminal "B" grounded, PCM will provide a ground for EGR solenoid. If power is present at solenoid, vacuum should now be blocked and EGR valve should not open.
3. With no power or ground supplied to EGR solenoid, vacuum should pass through solenoid. If vacuum does not pass through solenoid, vacuum hoses or EGR solenoid filter are plugged or EGR solenoid is faulty.

Code 32, Schematic, EGR Sys Error. Scheme 66

Code 32, Schematic, EGR Sys Error. Scheme 67

CODE 33: MAP SENS, SIGNAL VOLTAGE HIGH

CODE 33 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This test confirms Code 33 and determines if it is result of a hard failure or an intermittent condition. Code 33 will set when voltage signal reading is too high for greater than a precalibrated period of time, TPS voltage indicates throttle is closed and neither Code 21 nor 22 is present.
2. This step simulates conditions for a Code 34. If control module recognizes and sets Code 34, low MAP signal, control module and 5-volt reference and MAP signal circuits are not at fault. If ground circuit is shared with other sensors and ground circuit becomes open, additional codes related to these sensors may be set.

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

Code 33 Map Sens, Schematic, Signal Voltage High. Scheme 68

Code 33 Map Sens, Flow Chart, Signal Voltage High. Scheme 69

CODE 34: MAP SENS, SIGNAL VOLTAGE LOW

CODE 34 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This confirms Code 34 and determines if code was caused by a hard failure or an intermittent fault. 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 MAP signal to 5-volt reference at MAP harness connector will determine if sensor is at fault or if a problem exists with control module or wiring.
3. "Scan" tester may not display 12 volts. Control module recognizes voltage as greater than 4 volts (high MAP voltage signal), indicating control module and MAP signal circuit are not at fault.

With ignition switch in ON position and engine stopped, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparing BARO readings with a known good vehicle using same sensor is a good way to check accuracy of suspect sensor. Readings should be same within +/- .4 volt. A Code 34 will also result if 5-volt reference and MAP signal circuits are open or shorted to ground.

Code 34, Flow Chart, MAP Sens, Signal Voltage Low. Scheme 70

CODE 35: IAC IDLE SPEED ERROR

IAC is controlled by PCM using 4 pulse width modulated circuits. Code 35 will set when idle speed is greater or less than commanded (desired) idle speed.

Desired idle speed is based upon a look-up table built into PCM memory. This includes anything which requires an idle speed boost. Desired idle speed can be determined using a "Scan" tester. Cruise cable misadjustment may cause a high idle due to throttle plates being held open. Inspect IAC valve for dragging, binding and plugged passages.

Code 35, Schematic, IAC Idle Speed Error. Scheme 71

Code 35, Flow Chart, IAC Idle Speed Error. Scheme 72

CODE 41: EST CKT OPEN OR SHORTED

PCM monitors state of EST circuit and supplies an EST signal when engine is running (PCM is receiving RPM on reference circuit). DIS module has ability to control ignition coils in event of missing EST pulses from PCM. Code 41 will set if EST circuit is open, shorted to ground or shorted to voltage.

PCM will hold EST low if RPM reference is not received from ignition module. If Code 41 is set with Code 42, use CODES 41 & 42 SIMULTANEOUS chart.

Code 41, Flow Chart, EST Ckt Open Or Shorted. Scheme 73

Note. If Code Resets After Ignition Module Is Replaced, Replace PCM

Codes 41 & 42 Simultaneous, Flow Chart, By-pass Open Or Grounded. Scheme 74

CODE 42: BY-PASS OPEN OR SHORTED

PCM has an internal feedback to monitor state of by-pass circuit. Code 42 will set if by-pass circuit is open or shorted to ground at time of engine start-up. If Code 41 is set with Code 42, use CODES 41 & 42 SIMULTANEOUS chart.

Code 42, Flow Chart, By-Pass Open Or Shorted. Scheme 75

Check knock sensor signal circuit for a potential open or short to ground. An open knock signal circuit would cause 5-volt reference to remain high at ECM knock signal terminal. A short to ground in knock signal circuit would cause 5-volt reference signal to pull low to near zero volts. If either of these conditions exist for about 10 seconds, a Code 43 will set. Resistance to ground through knock sensor should be 3300-4500 ohms.

Code 43, Schematic, Esc Error. Scheme 76

Code 43, Flow Chart, Esc Error. Scheme 77

CODE 44: LEAN EXHAUST INDICATION

CODE 44 ECM TERMINAL & CKT WIRING IDENTIFICATION

O2 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 number refers to number on diagnostic chart.

1. Checks to see if O2 sensor is registering a lean condition. Code 44 is set when O2 sensor voltage signal at control module is low (less than .3 volt) for a precalibrated period and system is operating in "closed loop".

Using "Scan" tester, observe Block Learn Memory (BLM) value at different RPMs. If conditions for a Code 44 exist, block learn value will be about 150.

O2 Sensor Wire

O2 sensor wire may be mispositioned and laying against exhaust manifold. Check for ground between sensor and wire connector.

Fuel Contamination

Water, even small amounts, near in-tank fuel pump inlet can be delivered to injector. Water may cause a lean exhaust and set Code 44.

Fuel Pressure

System will be lean if fuel pressure is low. If necessary, 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.

Misfire Or Stall

If engine misfires or stalls (including running out of fuel) while vehicle is moving, a Code 44 may set. If Code 44 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Code 44, Flow Chart, Lean Exhaust Indication. Scheme 78

CODE 45: RICH EXHAUST INDICATION

CODE 45 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

O2 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. Diagnosis should begin with fuel pressure, leaking injector, HEI shielding (ground), vapor canister fuel saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.

Note. Test number refers to number on diagnostic chart.

1. Test checks to see 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 idle, O2 sensor signal at control module is greater than .7 volt for a precalibrated period and time since engine start is one minute or more.

If other codes of lower number are set with Code 45, use those charts first. Malfunction in MAP or TPS sensor circuits can cause a Code 45 to set. If other codes are not set, Code 45, rich exhaust, is most likely caused by

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. Control module can compensate for slight increases, but a Code 45 will be set if air/fuel ratio becomes too rich.

Ignition Ground

If an open occurs on HEI ground circuit, HEI induced electrical "noise" may result, causing simulated reference pulses to be picked up by control module on reference line of EST harness. Additional pulses result in a higher than actual engine speed signal. Control module will increase injector pulse width ("on" time) to match increased RPM signal. "Scan" tester will show higher than actual RPM, which can help in diagnosing this problem.

Evaporative Fuel Canister

Fuel saturation of charcoal canister will cause a rich air/fuel ratio. If canister is full of fuel, check canister control valves and hoses.

MAP Sensor

An output causing control module to sense a higher than normal manifold pressure (low vacuum) can cause system to go rich. Disconnecting MAP sensor will allow control module to substitute a fixed value for MAP sensor. If condition disappears, substitute a different 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 exterior of O2 sensor. False high signal voltage (low oxygen content sensed) produced is interpreted by control module as a rich mixture, causing control module to set Code 45.

EGR Problem

EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling.

Also check for shorted or leaking injector and fuel-contaminated oil. If Code 45 is intermittent, see INTERMITTENTS in the TESTS W/O CODES article in this section.

Code 45, Flow Chart, Lean Exhaust Indication. Scheme 79

CODE 46: POWER STEERING PRESSURE SWITCH

PCM supplies and monitors a 12-volt signal on power steering pressure switch circuit. Pressure switch is normally closed, pulling 12-volt signal low. When power steering pressure exceeds 450 psi (kg/cm 2 ), switch opens. Code 46 will set when vehicle speed is greater than 40 MPH and monitored circuit voltage is high (open) for more than 25 seconds.

Note. Test numbers refer to numbers on diagnostic charts.

1. Tests for normal operation of power steering switch. "Scan" testers will display this information differently. Refer to manufacturer operating manual for additional information.
2. If display does not change to normal (no pressure) when switch connector is removed, check for power steering switch signal circuit shorted to ground. If circuit is not shorted, ECM is faulty. If display changes to normal when switch connector is disconnected, switch is defective.
3. Determines if fault is switch or circuit. A jumpered connector should cause high pressure to be displayed, indicating wiring and ECM are okay. If high pressure is indicated and Code 46 is present, switch or switch connector is faulty.

Check harness for poor connections at ECM and switch. If connections and harness are okay, monitor switch status on a "Scan" tester while wiggling harness and connectors. An abrupt change in status indicates a problem.

Code 46, Schematic, Power Steering Pressure Switch. Scheme 80

Code 46, Flow Chart, Power Steering Pressure Switch. Scheme 81

CODE 49: IDLE RPM HIGH (VACUUM LEAK)

PCM can detect vacuum leaks that can cause idle speed to rise above control of IAC system. Code 49 is set when IAC is functioning properly and vacuum leaks are detected (engine idle speed cannot be reduced by IAC).

Inspect vacuum hoses for cracks and splits. If all hoses and connections are okay, check for intake manifold and MAP sensor leaks. Check minimum idle speed and PCV valve. A short to ground in a IAC circuit may cause a Code 49 to set.

Code 49, Idle RPM High (Vacuum Leak). Scheme 82

Code 49, Idle RPM High (Vacuum Leak). Scheme 83

CODE 51: FAULTY PROM/MEM-CAL

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

CODE 52: FAULTY CAL-PAK

Ensure all pins are fully inserted in socket. If pins are okay, replace CAL-PAK, clear memory and recheck. If Code 51 reappears, replace control module.

CODE 55: ECM ERROR

Ensure correct MEM-CAL or PROM is being used and that it is properly installed. If so, replace control module. Clear codes, confirm closed loop operation and check operation of SERVICE ENGINE SOON light.

CODE 82: INTERNAL PCM COMMUNICATION FAULT

PCM has diagnostic features that monitor communications between engine control module and transaxle control module within PCM. When a certain number of incorrect messages have been sent between engine and transaxle control modules or PCM has wrong calibration, PCM will set Code 82 in memory.

SUMMARY

If no hard fault codes are present, driveability symptoms exist 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. PCM/BCM CODE CHARTS

See also:
• BASIC TESTING
• TESTS W/O CODES
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