1.8l/2.5l Tbi Tests W/codes Pontiac Sunbird II

MODEL IDENTIFICATION

Repair procedures in this article are identified by body type. The following table lists GM division, model name, and body type.

MODEL IDENTIFICATION

DESCRIPTION

Note. Most Computer Command Control (CCC) problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the CCC system as a possible cause of problems, ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in lost diagnostic time.

The Computer Command Control (CCC) system used on the 1985 General Motors vehicles monitors as many as 19 engine/vehicle functions. This system controls engine operation and lowers exhaust emissions while maintaining good fuel economy and driveability. The Electronic Control Module (ECM) is the "brain" of the CCC system. The ECM controls as many as 12 engine related systems constantly adjusting engine operation.

The CCC system is primarily an emission control system, designed to maintain a 14.7:1 air/fuel ratio under all operating conditions. When the ideal air/fuel ratio is maintained, the catalytic converter can control oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) emissions.

ECM Operating Conditions Sensed

1. A/C "ON" or "OFF"
2. Engine Coolant Temperature
3. Ambient Temperature
4. Barometric Press. (BARO)
5. Brake "ON" or "OFF"
6. Cruise Control "ON" or "OFF"
7. Differential Press. (Eng. Vacuum)
8. Distributor Reference a) Crankshaft Position b) Engine Speed
9. EGR Vacuum
10. Engine Cranking
11. Engine Detonation (ESC)
12. Exhaust Oxygen (O2)
13. Manifold Absolute Press. (MAP)
14. Mass Air Flow (MAF)
15. Manifold Air Temperature (MAF)
16. Park/Neutral Sw. Position (P/N)
17. System Voltage
18. Throttle Position (TPS)
19. Transmission Gear Position Vehicle Speed (VSS)

ECM Systems Controlled

1. A/C
2. Air Management
3. Canister Purge
4. Diagnostics a) Check Eng. Light b) Data Output (ALCL) c) Diagnostic Test
5. Terminal (ALCL)
6. Early Fuel Evaporation (EFE)
7. Electric Fuel Pump
8. Electronic Fuel Inj. (TBI & Port)
9. Electronic Spark Control (ESC)
10. Electronic Spark Timing (EST)
11. Engine Cooling Fan
12. Exhaust Gas Recirculation (EGR)
13. Fuel Control (M/C solenoid)
14. Hood Louvre
15. Idle Air Control (IAC)
16. Idle Speed (ISC. ILC ISS)
17. Transmission Converter Clutch (TCC)
18. Turbo Wastegate

Schematic of Computer Command Control System. Scheme 65

Sectional View of Mixture Control Solenoid. Note air bleed above main metering rod. Scheme 66

DIAGNOSTIC SYSTEM OPERATION

Note. A "CHECK ENGINE" lamp driver is installed in the wiring harness from ECM to the "CHECK ENGINE" lamp. This driver amplifies the power to the "CHECK ENGINE" lamp to reduce amperage draw on the battery.

The ECM of the CCC system is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, the ECM will light the Amber "CHECK ENGINE" lamp located on the instrument panel. When the malfunction is detected and the lamp is turned on, a corresponding trouble code will be stored in the ECM memory. Malfunctions are recorded as "hard failures" or as "intermittent failures".

1. "Hard failures" cause the "CHECK ENGINE" lamp to glow and remain on until the malfunction is repaired. If the "CHECK ENGINE" lamp comes on and remains on during vehicle operation, the cause of the malfunction must be determined.
2. "Intermittent failures" cause the "CHECK ENGINE" lamp to flicker or go out after about 10 seconds when the fault goes away. However, the corresponding trouble code will be retained in the ECM memory. "Intermittent failures" may be sensor related. If a sensor fails, the ECM will use a substitute value in its calculations to continue engine operation. In this condition, service is not mandatory; but loss of good driveability may be encountered. If the related fault does not reoccur within 50 engine restarts, the related trouble code will be erased from the ECM memory.

As a bulb and system check, the "CHECK ENGINE" lamp will glow when the ignition switch is turned on and the engine is not running. When the engine is started, the lamp should go out. If not, a malfunction has been detected in the CCC system.

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.

BASIC DIAGNOSTIC PROCEDURE

Diagnosis of the CCC system should be performed in the following order

1. Make sure that all engine systems not related to the CCC system are operating properly. Do not proceed with testing unless all other problems have been repaired.
2. Put the system into diagnostic mode and record trouble codes flashed by "CHECK ENGINE" light. Exit the diagnostic mode.
3. If trouble codes were displayed, decide whether the codes are "hard" or "intermittent" trouble codes.
4. Proceed to Diagnostic Circuit Check chart. Follow all instructions given in that chart.
5. If no trouble codes were displayed, proceed to System Performance Check for carbureted models, or Field Service Mode for fuel injection models.
6. If no trouble is indicted by any of these charts, use the TROUBLE SHOOTING material in the CCC TESTS W/O CODES article in this section. The comments there will send you to the proper component charts or tell you what to fix.
7. After any repairs are made, perform System Performance Check. Clear any trouble codes.

Note. Each of the steps listed here are described later in this section. If you are unsure of the proper way to test, read through the following material.

Scheme 67

1. Turn ignition switch on but do not start engine. "CHECK ENGINE" light should glow. Locate assembly line data link (ALDL) connector attached to ECM wiring harness under instrument panel. Insert spade lug terminal across "TEST" terminal and "GROUND" terminal. (Scheme 67) CAUTION: Inserting spade lug in terminals of ALDL connector grounds "TEST" terminal lead. Do not ground ALDL connector until after ignition is on or engine is started. (Scheme 67): ALDL Connector Terminal Locations
2. "CHECK ENGINE" light should flash code "12". Code "12" consists of "FLASH", pause, "FLASH", "FLASH" followed by a longer pause. Trouble Code "12" will be repeated 2 more times, then if any trouble codes are stored in the ECM memory, they will be displayed in the same manner.
3. Trouble codes will be displayed from lowest to highest numbered codes (3 times each) and be repeated as long as the "TEST" terminal of the ALDL connector is grounded.
4. To exit diagnostic mode, turn ignition switch off and remove spade lug terminal from ALDL connector.

CLEARING TROUBLE CODES

Turn ignition switch on and ground "TEST" lead at ALDL connector. Turn ignition switch off and remove ECM fuse from fuse block for 10 seconds. Remove "TEST" lead ground.

READING TROUBLE CODES

The ECM stores component failure information for CCC system under a related trouble code which can be recalled for diagnosis and repair. When recalled, these codes will be displayed by flashes of the "CHECK ENGINE" light. Trouble codes are displayed starting with the lowest numbered code. Only codes that represent a definite malfunction will be shown.

Note. Chevette and 1000 models (Minimum Function system) do not have "long-term" memory capability. Codes in the memory will be erased when ignition switch is turned off. Diagnostic ability exists only while engine is running and malfunction exists.

Trouble codes are read by counting flashes of the "CHECK ENGINE" light, or by reading the output of a diagnostic tool connected to the ALDL connector under the dashboard. The tool is faster and more accurate, but is not mandatory.

If the tool is not available, read the flashes of the dashboard light. For example, "FLASH", "FLASH", pause, "FLASH", longer pause, identifies "21". The first series of flashes are the first digit of trouble code; second series of flashes are the second digit of trouble code.

Note. On EFI models only, "CHECK ENGINE" light will indicate operational mode of engine. In closed loop, the "CHECK ENGINE" light will flash at a rate of 1 flash per second. In open loop, the "CHECK ENGINE" light will flash at a rate of 2.5 flashes per second.

TROUBLE CODE COMPONENT IDENTIFICATION

ECM TROUBLE CODE IDENTIFICATION

TROUBLE CODE DETERMINATION (HARD OR INTERMITTENT)

During any diagnostic procedure, you must decide between "hard failure" codes and "intermittent failure" codes. Diagnostic charts will not usually help analyze "intermittent failure" codes. To determine "hard failure" codes and "intermittent failure" codes, proceed as follows

1. Enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode and clear trouble codes.
2. Apply parking brake and place transmission in Neutral (man. trans.) or "P" (auto. trans.). Block drive wheels and start engine. "CHECK ENGINE" light should go out. Run warm engine at specified curb idle for 2 minutes and note "CHECK ENGINE" light.
3. If "CHECK ENGINE" light comes on, enter diagnostic mode. Read and record trouble codes. This will reveal "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. NOTE: Anytime codes "51", "52", "54" or "55" are displayed with another code, start with "50-series" code first, then proceed to lowest numbered code.
4. If "CHECK ENGINE" light does not come on, all stored trouble codes were "intermittent failures". Exceptions are noted under Diagnostic Procedure.

DIAGNOSTIC MATERIALS

Note. The charts described in the following paragraphs are arranged later in this article, by engine size and fuel system type.

DIAGNOSTIC CHARTS

The Diagnostic Charts are used to find and repair problems which the On-Car Diagnostics have found. These charts include

1. Charts which fix a problem when the On-Car Diagnostics don't work.
2. Charts where a stored trouble code leads you to a particular problem.
3. Charts which are used because the Field Service Mode found a problem.
4. "Engine Cranks But Won't Run" charts.

DIAGNOSTIC CIRCUIT CHECK

1. If complaint is "CHECK ENGINE" lamp related, this check will lead to the most likely problem area, if a malfunction exists. Enter diagnostic mode and record stored trouble codes. Begin diagnosis with the lowest numbered code shown and go to the numbered trouble code chart.
2. If code "51" is displayed, see PROM removal and installation in this article. If codes "54" or "55" are displayed with another code, always refer to diagnostic chart for code "54" or "55" first, then proceed to next lowest numbered code.

DIAGNOSTIC SYMPTOM CHECK

1. If complaint is not "CHECK ENGINE" lamp related, this check will lead to most likely problem area. However, first make checks that would normally be made for the complaint on a vehicle without CCC system.
2. Follow instructions in diagnostic chart and repair malfunction. After repair, perform System Performance Check (carbureted models) or Field Service Mode Check (EFI models).

FIELD SERVICE MODE CHECK (EFI MODELS ONLY)

1. This test confirms proper operation of fuel system and verifies closed loop operation. Clear codes and perform this test after any repair is completed.
2. When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on front-wheel drive models does not hold drive wheels.
3. On some engines, the oxygen sensor will cool off after only a short period of time while engine is idling. This will cause engine to go into open loop. To restore closed loop mode, run engine at part throttle several minutes and accelerate from idle to part throttle several times.

Note. Although there are many charts connected with CCC diagnosis, only 2 charts are needed to prove the system is operating properly. Normally, only 3 charts are necessary to find a problem, if one exists.

DIAGNOSTIC TOOLS

The CCC system does not require special tools for diagnosis. A tachometer, a dwell meter, test light, ohmmeter, digital voltmeter with 10 megohms impedance (minimum), vacuum pump, vacuum gauge and 6 jumper wires 6" long (1 wire with female connectors at both ends; 1 wire with male connector at both ends; 4 wires with male and female connectors at opposite ends) are the only tools necessary for diagnosis.

Note. Special testers can be used to read trouble codes and check voltages in the system. These tools can save a great deal of time, but are not required. Refer to tester manual for operating procedures.

A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

On carbureted models, the dwell meter is used to measure the time the M/C solenoid is on or off. This indicates if the M/C solenoid is working and the fuel mixture strength (rich or lean). The dwell meter is set on the 6-cylinder scale regardless of the number of cylinders in the engine.

Dwell meter is connected to Green connector located near the carburetor. This connector will not be connected to any circuit EXCEPT when you are testing with the dwell meter. DO NOT allow terminal wire to come in contact with any ground source, including rubber hoses.

Note. If engine operation seems to change when the dwell meter is connected to Green wire, remove dwell meter and use another type. A few brands are not compatible with CCC system.

If engine is at operating temperature and idling, dwell meter needle should be varying between 10-50°. This indicates closed loop operation. If needle does not move, open loop operation is indicated.

Diagnostic Circuit Check Flow Chart. Scheme 68

DIAGNOSTIC CIRCUIT CHECK FLOW CHART. Scheme 69

CHART A1 - NO "CHECK ENGINE" LIGHT

The "CHECK ENGINE" light should come on when ignition is turned "ON" and engine is not running. Battery voltage is supplied directly to bulb. The ECM controls the light by grounding circuit 419.

If engine runs, no "CHECK ENGINE" light indicates a defective bulb, blown fuse or open control circuit 419. If engine cranks but will not run, no "CHECK ENGINE" light indicates a blown battery fuse, blown fusible link, ECM ignition fuse blown, battery circuit 340 to ECM open, ignition circuit 439 to ECM open or poor connection to ECM.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Solenoids and relays are turned "ON" or "OFF" by ECM, using electronic switches called "drivers". Each driver is part of a group of 4, called "Quad-Drivers". Failure of 1 driver can damage other drivers in set. Solenoid and relay coil resistance must be more than 20 ohms, as less resistance will cause early failure of ECM drivers.

Chart A1 Schematic, No "CHECK ENGINE" Light. Scheme 70

Flow Chart A1, No "CHECK ENGINE" Light. Scheme 71

Flow Chart A1, No "CHECK ENGINE" Light. Scheme 72

CHART A2 - NO CODE 12, "CHECK ENGINE" LIGHT ON STEADY

The "CHECK ENGINE" light should come on when ignition is turned "ON" and engine is not running. Battery voltage is directly supplied to bulb. The ECM controls the light by grounding circuit 419. With diagnostic terminal grounded, light should flash Code 12, followed by other trouble codes stored in memory. A steady light indicates a grounded circuit 419 or an open diagnostic circuit 451.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. If the light goes off when the ECM connector is disconnected, then circuit 419 is not shorted to ground. Check connector terminals physically for proper contact.
2. This step checks for an open diagnostic circuit 451.
3. At this point wiring is okay, problem may be a faulty ECM or PROM. If Code 51 is stored when PROM is removed, replace PROM.
4. Solenoids and relays are turned "ON" or "OFF" by ECM, using electronic switches called "drivers". Each driver is part of a group of 4, called "Quad-Drivers". Failure of 1 driver can damage other drivers in set. Solenoid and relay coil resistance must be more than 20 ohms, as less resistance will cause early failure of ECM drivers.

Chart A2 Schematic, No Code 12 ("CHECK ENGINE" Light On Steady). Scheme 73

Flow Chart A2, No Code 12 ("CHECK ENGINE" Light On Steady). Scheme 74

Flow Chart A2, No Code 12 ("CHECK ENGINE" Light On Steady). Scheme 75

CHARTS A3 & A4 - ENGINE CRANKS BUT WON'T RUN

Note. The following step numbers refer to the step numbers in the accompanying Flow Charts.

1. 1) A "CHECK ENGINE" light "ON" checks for ignition and battery supply to ECM.
2. 2) Fuel spray from injector indicates that fuel is available, check engine for flooding.
3. 3) While cranking engine there should be no fuel spray with injector disconnected. Replace injector if it sprays or if it drips.
4. 4) If injector is okay, fuel system appears to be operating normally. Using ST-125 spark gap tool, check voltage at spark plugs. No spark indicates an HEI problem. If spark is satisfactory, check the following; Throttle Position Sensor (TPS) for sticking or binding in wide open throttle position. Check coolant sensor "OPEN" signal to ECM using Code 15 chart. Check for ice (cold weather) or foreign material in fuel, engine may start after 5-6 minutes in heated shop. Check for EGR sticking open, open crank signal (cold weather), low fuel pressure or volume (lean air/fuel ratio) See CHART A5.
5. 5) The EFI system is considered okay, if no trouble was found. Reconnect injector and look for possible mechanical problems.
6. 6) No spray from injector indicates a faulty fuel system or no ECM control of injector. If test light "blinks" while cranking, ECM control is considered okay. Light may dim while "blinking", use bulb 1847 or equivalent.
7. 7) Circuit 439 supplies ignition voltage to injector. Using a test lamp, probe each connector terminal. Test lamp should light on 1 terminal, confirming voltage at connector. The ECM injector circuit 467 may be open, reconnect injector. Using test lamp, probe terminal 8 of White ECM connector. A light at this point indicates that injector drive circuit is okay.
8. 8) No "blinking" light indicates no ECM control of injector. With voltmeter on AC 2 volt range, voltage should be greater than .7 volts. If voltage is less than .7 volts, there is an open or short to ground in HEI reference circuit 430. If circuit is okay, there is an HEI problem.
9. 8A) Disconnect distributor connector. Momentarily touch ECM side of connector, circuit 430, with a test lamp connected to 12 volts. Note injector as contact is made, injector should turn on. If injector turns on, ECM circuit is okay. Connect spark tool ST-125 and check for spark. If spark is okay, HEI module is faulty. No spark indicates an HEI problem.

Chart A3 & A4 Schematic (1.8L), Engine Cranks But Won't Run. Scheme 76

Chart A3 & A4 Schematic (2.5L), Engine Cranks But Won't Run. Scheme 77

Flow Chart A3, Engine Cranks But Won't Run. Scheme 78

Flow Chart A3, Engine Cranks But Won't Run. Scheme 79

Flow Chart A4, Engine Cranks But Won't Run (Cont.). Scheme 80

Flow Chart A4, Engine Cranks But Won't Run (Cont.). Scheme 81

CHART A5 - FUEL SYSTEM DIAGNOSIS

The ECM turns in-tank fuel pump on as long as ignition is "ON" and the engine is cranking or running. The ECM will allow the pump to run as long as it receives reference pulses from distributor. If there are no reference pulses, the ECM will shut off the fuel pump within 2 seconds after key is "ON". The fuel pump test terminal is located on left side of engine compartment. When engine is stopped, pump can be turned "ON" by applying battery voltage to test terminal. Improper fuel system pressure will result in one or all of the following symptoms: Cranks but will not run, Code 44, Code 45, engine cuts out (may feel like ignition problem), poor fuel economy, loss of power and hesitation.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. If the fuse is blown, this test will confirm a short to ground on circuit 120. To prevent mis-diagnosis, be sure fuel pump is disconnected before test.
2. This test determines if pump circuit is ECM controlled. The ECM will turn pump relay on, then turn it off after 2 seconds, if engine is not cranking or running.
3. This step turns fuel pump on, if circuit 120 wiring is okay.
4. This step checks for battery voltage at fuel pump relay.

Chart A5 Schematic, Fuel System Diagnosis. Scheme 82

Flow Chart A5, Fuel System Diagnosis. Scheme 83

Flow Chart A5, Fuel System Diagnosis (1 Of 2). Scheme 84

CHART A6 - FUEL SYSTEM DIAGNOSIS

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. 5) This step checks relay ground circuit No. 450.
2. 6) This step checks ECM control of relay through circuit 465.
3. 7) The fuel pump circuit includes an engine oil pressure switch. If fuel pump relay fails, the fuel pump will continue to run via oil pressure switch circuit. Relay failure will result in extended cranking times and possible no start condition.
4. 8) This test checks the oil pressure switch to be sure it provides battery feed to fuel pump if pump relay fails.
5. 9) This test checks for open oil pressure switch with ignition "OFF". Should switch stick closed, fuel pump will continue to run and discharge battery.

Flow Chart A6, Fuel System Diagnosis. Scheme 85

From Chart A-5

Flow Chart A6, Fuel System Diagnosis (2 Of 2). Scheme 86

CHART A7 - FUEL SYSTEM DIAGNOSIS

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Pressure below 9 psi falls into 2 categories: If regulated pressure is less than 9 psi and volume to injector is adequate, system will run lean and cause Code 44. Engine will be hard to start when cold and have poor overall performance. A restricted fuel flow is causing pressure drop. Normally, a vehicle with fuel pressure of less than 9 psi at idle will not be driveable. However, if pressure drop occurs only when driving, the engine will surge then stop as pressure begins to drop.
2. Restricting the fuel return line allows the fuel pump to develop its maximum pressure. When battery voltage is applied to pump test terminal, pressure should be between 13 to 18 psi.
3. This test determines if high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.

Chart A7 Schematic, Fuel System Diagnosis. Scheme 87

Flow Chart A7, Fuel System Diagnosis. Scheme 88

Flow Chart A7, Fuel System Diagnosis. Scheme 89

CODE 13 - OPEN OXYGEN SENSOR CIRCUIT

Code 13 will set: At least 2 minutes after engine start, with O2 signal voltage steady between .35 and .55 volt for more than 1 minute, and with throttle position sensor signal above 6% (1200 RPM). The ECM supplies voltage of about .45 volt between terminals 8 and 15. (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The O2 sensor varies the voltage within a range of about 1 volt (rich exhaust) to .1 volt (lean exhaust). The O2 sensor is like an open circuit and produces no voltage when it is below about 600°F (360°C). An open sensor circuit or cold sensor causes open loop operation.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Grounding diagnostic terminal with engine running activates "Field Service Mode". This allows the ECM to confirm either open or closed loop operation using the "CHECK ENGINE" light.
2. This step verifies that no additional codes are stored, and that Code 13 is intermittent. See the CCC TESTS W/O CODES article in this section.
3. This step simulates a lean exhaust. If ECM and wiring are okay, the ECM will see the lean condition and turn the "CHECK ENGINE" light off for at least 30 seconds after engine start, and then flash "open loop". It is considered normal if light remains off for a longer period of time before flashing open loop.

Code 13 Schematic, Open O2 Sensor Circuit. Scheme 90

Code 13 Flow Chart, Open O2 Sensor Circuit. Scheme 91

Code 13 Flow Chart, Open O2 Sensor Circuit. Scheme 92

CODE 14 - COOLANT SENSOR SIGNAL VOLTAGE LOW

The Coolant Temperature Sensor uses a thermistor to control signal voltage to the ECM. The ECM applies voltage on circuit 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see a high signal voltage. As the engine warms, the sensor resistance becomes less. The voltage signal will be about 1-1.5 volts at terminal 4 of ECM. Code 14 will set if signal voltage indicates a coolant temperature above 275°F (135°C) for more than 2 seconds. Coolant temperature is one of the inputs used to control fuel delivery, engine timing (EST), idle (IAC), and converter clutch (TCC).

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. If voltage is above 4 volts, the ECM and wiring are okay. If checking resistance at coolant sensor is difficult because of sensor location, disconnect Black ECM connector and check resistance between terminals 4 and 11.

Code 14 Schematic, Coolant Sensor Signal Voltage Low. Scheme 93

Code 14 Flow Chart, Coolant Sensor Signal Voltage Low. Scheme 94

Code 14 Flow Chart, Coolant Sensor Signal Voltage Low. Scheme 95

CODE 15 - COOLANT SENSOR SIGNAL VOLTAGE HIGH

The Coolant Temperature Sensor uses a thermistor to control signal voltage to the ECM. The ECM applies voltage on circuit 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see a high signal voltage. As the engine warms, the sensor resistance becomes less and voltage drops. At normal engine operating temperature, voltage will be about 1-1.5 volts at terminal 4 of ECM.

Code 15 will set if signal voltage indicates a coolant temperature less than -31°F (-35°C) for more than 4 seconds or if time since engine start is more than 1 minute. Coolant temperature is one of the inputs used to control fuel delivery, engine timing (EST), idle (IAC), and converter clutch (TCC).

If coolant circuit 410 opens with ignition "OFF", the ECM will see -40°F (-40°C) and deliver fuel for this temperature. If actual temperature is above 20°F (-7°C), the engine will not start due to rich mixture unless "Clear Flood" is used by fully depressing accelerator. Engine will start using "Clear Flood". However, "CHECK ENGINE" light will not come on and code will not be stored, until engine has run for 1 minute.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. If voltage is above 4 volts, the ECM and wiring are OK. If location of sensor makes it hard to check, disconnect Black ECM connector and check resistance between connector terminals 4 and 11.

Code 15 Flow Chart, Coolant Sensor Signal Voltage High. Scheme 96

Code 15 Flow Chart, Coolant Sensor Signal Voltage High. Scheme 97

CODE 21 - TPS SIGNAL VOLTAGE HIGH

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to throttle valve. Signal voltage will vary from less than 1.25 volts at idle to 4.5 volts at wide open throttle. Code 21 will set if: TPS voltage is greater than 2.5 volts for 2 seconds, engine speed is less than 1600 RPM or if MAP is less than 9 psi or equal to a no load condition.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. This test confirms Code 21, and that fault is present.
2. This test simulates Code 22. If the ECM recognizes the low voltage signal and sets Code 22, the ECM and wiring are okay.

Code 21 Schematic, TPS Signal Voltage High. Scheme 98

Code 21 Flow Chart, TPS Signal Voltage High. Scheme 99

Code 21 Flow Chart, TPS Signal Voltage High. Scheme 100

CODE 22 - TPS SIGNAL VOLTAGE LOW

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to throttle valve. Signal voltage will vary from less than 1.25 volts at idle to 4.5 volts at wide open throttle. Code 22 will set if engine is running, TPS voltage is less than .2 volts for 2 seconds and engine speed is less than 1600 RPM.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. This test confirms Code 22, and that a fault is present.
2. This test simulates Code 21. If the ECM recognizes high voltage signal and sets Code 21, the ECM and wiring are okay.
3. This test checks for reference voltage from the ECM. To prevent damage to ECM, be sure to disconnect connector when checking circuit wiring for open or shorts to ground.

Code 22 Flow Chart, TPS Signal Voltage Low. Scheme 101

Code 22 Flow Chart, TPS Signal Voltage Low. Scheme 102

CODE 24 - VEHICLE SPEED SENSOR (VSS)

The ECM applies and monitors 12 volts on circuit 437. Circuit 437 connects to Vehicle Speed Sensor (VSS) which alternately grounds circuit when drive wheels are turning. This pulsing action takes place 2000 times per mile. The ECM calculates vehicle speed based on the time between "pulses".

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. This test monitors the ECM voltage on circuit 437. With wheels turning, the pulsating action will result in a varying voltage. The variation will be greater at low speeds to an average of 4-6 volts at about 20 MPH.
2. A voltage of less than 1 volt at ECM connector indicates that circuit 437 is shorted to ground. Disconnect 437 at VSS. If voltage now reads above 10 volts, the VSS is faulty. If voltage remains less than 10 volts, circuit 437 is grounded. If circuit 437 is not grounded, check for faulty ECM connector or ECM.
3. A steady 8-12 volts at ECM connector indicates circuit 437 is open or a faulty VSS.
4. This normal voltage condition indicates a possible intermittent problem. See the CCC TESTS W/O CODES article in this section.

Code 24 Schematic, Vehicle Speed Sensor (VSS). Scheme 103

Code 24 Flow Chart, Vehicle Speed Sensor (VSS). Scheme 104

Code 24 Flow Chart, Vehicle Speed Sensor (VSS). Scheme 105

CODE 33 - MAP SENSOR SIGNAL VOLTAGE HIGH

The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4-4.5 volts at wide open throttle. If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery.

Code 33 will set when signal reading is too high for a time greater than 8 seconds and if the TPS voltage indicates throttle is closed. Engine misfire or a low and unstable idle may set Code 33. Disconnect MAP sensor and system will go to back-up mode. If misfire or idle condition remains, see the CCC TESTS W/O CODES article in this section.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. This test confirms Code 33, and that fault is present.
2. If the ECM recognizes and sets Code 34, low MAP signal, the ECM and wiring are okay.

Code 33 Schematic, MAP Sensor Signal Voltage High. Scheme 106

Code 33 Flow Chart, MAP Sensor Signal Voltage High. Scheme 107

Code 33 Flow Chart, MAP Sensor Signal Voltage High. Scheme 108

CODE 34 - MAP SENSOR SIGNAL VOLTAGE LOW

The Manifold Absolute Pressure sensor (MAP) responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4-4.5 volts at wide open throttle. If MAP sensor fails the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery. Code 34 will set when signal reading is too low and ignition is turned on.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. This test confirms Code 34, and that fault is present.
2. If the ECM recognizes and sets Code 33, high MAP signal, the ECM and wiring are okay.

Code 34 Flow Chart, MAP Sensor Signal Voltage Low. Scheme 109

Start Non-Scan

Code 34 Flow Chart, MAP Sensor Signal Voltage Low. Scheme 110

CODE 35, IDLE AIR CONTROL (IAC)

The ECM controls engine idle speed by moving the Idle Air Control (IAC) valve to control airflow around throttle valve plate. It does this by sending voltage pulses called "counts" or "steps" to proper motor winding. The motor shaft and valve move a given distance for each pulse received.

1. To increase idle speed, the ECM sends enough counts to retract IAC valve and increase airflow until idle speed reaches proper RPM.
2. To decrease idle speed, the ECM sends enough counts to extend IAC valve and reduce airflow. This will reduce ECM counts.

The ECM "learns" to correct valve position to maintain proper idle RPM. If the "learned" IAC valve is correct, the ECM will command a reset. The reset will occur after the next engine start and vehicle speed is greater than 35-45 MPH.

The following are diagnostic aids

1. Park/Neutral switch (auto. trans. only). If the ECM thinks the vehicle is always in Neutral, idle speed will not be correct in Drive range. See CHART C-1A.
2. A leaking injector will cause poor idle quality due to excess fuel.
3. A sticking injector causing too lean or too rich condition can cause a poor idle condition. A Code 44 or Code 45 may be stored.
4. A sticking throttle shaft or binding linkage causes a high TPS voltage (open throttle indication). The ECM does not recognize a closed throttle and will not control idle. Monitor TPS voltage, voltage should read less than 1.2 volts with throttle closed.
5. EGR on while idling will cause roughness, stalling and hard starting. See CHART C-7A.
6. Battery cables and ground straps should be clean and secure, erratic voltage will cause IAC to change its position resulting in poor idle quality.
7. ECM should compensate for power steering loads. Loss of this signal will be most noticeable when parking and steering loads are high.
8. IAC valve will not move if system voltage is below 9 or greater than 17.8 volts.

Code 35 Schematic, Idle Air Control (IAC). Scheme 111

Code 35 Flow Chart, Idle Air Control (IAC). Scheme 112

Code 35 Flow Chart, Idle Air Control (IAC). Scheme 113

CODE 42 - ELECTRONIC SPARK TIMING (EST)

Code 42 indicates the ECM has seen an open or short to ground in EST or by-pass circuits.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. This test confirms Code 42, and that fault is present.
2. This test checks for a normal EST ground path through the ignition module. If circuit 423 is shorted to ground, reading will be less than 500 ohms.
3. As test lamp voltage touches circuit 423, the module should switch. This will cause the ohmmeter to "overange" if meter is in the 1000-2000 ohm position. A higher ohm range will indicate over 5000 ohms. This test assures that the module "switched".
4. If module did not switch, this step will test for a short in circuit 423, an open in circuit 424, and a faulty ignition module connection or module.
5. This step confirms that Code 42 is a faulty ECM and not an intermittent problem in circuits 423 and 424.

Code 42 Schematic (1.8L), Electronic Spark Timing (EST). Scheme 114

Code 42 Schematic (2.5L), Electronic Spark Timing (EST). Scheme 115

Code 42, Electronic Spark Timing (EST). Scheme 116

Code 42, Electronic Spark Timing (EST). Scheme 117

CODE 44 - LEAN EXHAUST INDICATION

The ECM supplies a voltage of about .45 volt between circuits 412 and 413. The O2 sensor varies the voltage from 1 volt (rich exhaust) to .10 volt (lean exhaust). The sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is below 600°F (310°C). An open sensor circuit or cold sensor causes open loop operation. Code 44 is set when O2 sensor signal at ECM is below .2 volts for 8 seconds or more or if time since engine start is 1 minute or longer.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Grounding diagnostic test terminal with engine running, activates the "Field Service Mode" and allows the ECM to confirm either open or closed loop operation.
2. A light out or "open loop" indicates presence of fault. Disconnecting O2 sensor will raise signal voltage above .2 volt. If the ECM and wiring are okay, the ECM should recognize the higher voltage, .35 to .55 volt and flash "open loop" when engine is started.
3. Code 44 may be set by any of the following conditions: Circuit 413 open (circuit 412 voltage will be over 1 volt), low fuel pressure, fuel contamination, EGR stuck open or malfunctioning MAP sensor. If these items are okay, and instructions at top of chart set Code 44, "CHECK ENGINE" light is "OFF" more than "ON" or flashing "open loop", oxygen sensor is faulty.

Code 44 Schematic, Lean Exhaust Indication. Scheme 118

Code 44 Flow Chart, Lean Exhaust Indication. Scheme 119

Code 44 Flow Chart, Lean Exhaust Indication. Scheme 120

Field Service Mode

1. Engine Running, Diagnostic Terminal Grounded
2. Open Loop - "Check Engine" Light Flashing At A Rate Of 2 Times Per Second
3. Closed Loop - "Check Engine" Light Flashes At A Rate Of 1 Time Per Second

CODE 45 - RICH EXHAUST INDICATION

The ECM supplies a voltage of about .45 volt between circuits 412 and 413. The O2 sensor varies the voltage from 1 volt (rich exhaust) to .10 volt (lean exhaust). The sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is below 600°F (310°C). An open sensor circuit or cold sensor causes open loop operation. Code 45 is set when O2 sensor signal at ECM is above .7 volts for 1 second and time since engine start is 1 minute or more.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Grounding diagnostic test terminal with engine running, activates the "Field Service Mode" and allows the ECM to confirm either open or closed loop operation.
2. A steady light or "open loop" indicates presence of fault. Grounding circuit 412 causes a low O2 sensor signal voltage. If the ECM and wiring are okay, the ECM should recognize the low voltage, and confirm lean signal by turning "CHECK ENGINE" light for at least 30 seconds.
3. Code 45 will not be set by a faulty O2 sensor. Code 45 indicates a rich exhaust and diagnosis should begin with these items: Fuel pressure, leaking injector, HEI shielding, canister purge saturation, coolant sensor, MAP sensor, and TPS intermittent output.

Code 45 Schematic, Rich Exhaust Indication. Scheme 121

Code 45 Flow Chart, Rich Exhaust Indication. Scheme 122

Code 45 Flow Chart, Rich Exhaust Indication. Scheme 123

CODE 51 - FAULTY PROM

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

CODE 55 - FAULTY ELECTRONIC CONTROL MODULE (ECM)

Replace ECM. Clear codes, confirm "closed loop" operation and check for no "CHECK ENGINE" light.

CHART C1 - ECM REPLACEMENT CHECK CHART

In order to reduce incidents of repeat ECM failure, a revised ECM diagnostic procedure is available. Beginning in 1982, most ECMs are equipped with Integrated Circuits (IC) in place of separate transistors to operate various controlled components.

These ICs, called Quad-Drivers (QDR), have 4 separate outputs, meaning that each QDR can operate up to 4 different components. An inoperative QDR can result in ECM output becoming open or shorted to ground. Often, all 4 outputs of a QDR will fail, even if just one QDR circuit is faulty.

Refer to the following tables to determine which ECMs contain QDRs. Since this procedure is not applicable to ECMs which do not contain QDRs, those ECMs are not listed.

Performing the diagnostic flow chart will identify an inoperative QDR. Once the circuit is identified, it must be repaired to eliminate repeat ECM failure. This diagnostic procedure must be used when "Replace ECM" is the conclusion of any procedure.

ECM QDR IDENTIFICATION (TBI/PFI)

ECM QDR IDENTIFICATION (CARBURETED)

ECM QDR IDENTIFICATION (PFI)

ECM QDR IDENTIFICATION (TBI)

ECM QDR IDENTIFICATION (TBI)

Scheme 124

CHART C1A - PARK/NEUTRAL SWITCH CHECK (AUTO TRANS MODELS)

The park/neutral switch contacts are part of neutral start switch, are closed to ground in park or neutral, and open in drive ranges. The ECM supplies ignition voltage through a current limiting resistor to circuit No. 434, and senses a closed switch when voltage on circuit No. 434 drops to less than one (1) volt. The ECM uses this signal as one of the inputs to control IAC and VSS diagnostics.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Checks for closed switch to ground in park position. Use an ohmmeter instead of a test light to 12 volts. Resistance will be low indicating continuity to ground.
2. Checks for an open switch in drive range. Use an ohmmeter instead of a test light to 12 volts. Resistance will be high or infinity, indicating an open switch.
3. Checks to this point indicate park/neutral switch and wiring are okay. The ECM signal voltage on circuit No. 434 may be missing. To check, reconnect ECM. Either back probe ECM connector circuit No. 434 with selector in drive or disconnect park/neutral switch. Probe harness connector circuit No. 434 with a voltmeter to ground.

Chart C1A, Park/Neutral Switch (Auto. Trans. Models). Scheme 125

Chart C1A, Park/Neutral Switch (Auto. Trans. Models). Scheme 126

CHART C1B - CRANK SIGNAL CHECK

Crank signal is a 12-volt signal to ECM during cranking to allow enrichment and cancel diagnostics until engine is running or 12 volts is no longer on circuit.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Checks for normal (cranking) voltage to terminal 1 of ECM. Test light should be on during cranking.
2. Checks to determine if source of blown fuse was faulty ECM.

Chart C1B, Crank Signal. Scheme 127

Chart C1B, Crank Signal. Scheme 128

CHART C1D - MAP OUTPUT CHECK

The MAP sensor measures manifold pressure (vacuum) and sends that signal to ECM. The ECM uses this information for fuel and spark control.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Check MAP sensor output voltage to ECM. This voltage, without engine running, represents a barometer reading to ECM.
2. Applying 34 kPa vacuum to MAP sensor should cause voltage to be 1.2 volts less than voltage at step 1). Upon applying vacuum to sensor, change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.
3. Check vacuum hose to sensor for leaking or restriction. Be sure no other vacuum devices are connected to MAP hose.

Chart C1D, MAP Output Check. Scheme 129

Chart C1D, MAP Output Check. Scheme 130

CHART C1E - P/S PRESSURE SWITCH SIGNAL

The power steering pressure switch is normally open to ground, and circuit No. 495 will be near battery voltage. Turning steering wheel increases power steering oil pressure, and its load on an idling engine. The pressure switch will close before load can cause an idle problem. Closing switch causes circuit No. 495 to read less than one (1) volt. The ECM will increase idle air rate and retard timing. A pressure switch that will not close, or an open circuit No. 495 or 450 may cause engine to stop when power steering loads are high. A switch that will not open, or a circuit No. 450 or 495 shorted to ground, will cause timing to retard at idle and may effect idle quality.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Checks for ECM signal voltage on circuit No. 495, and confirms ground circuit No. 450 is okay.
2. Maximum resistance, or infinity, indicates an open switch.
3. Less than one (1) ohm indicates that switch is closed when power steering pressure is high. Switch is okay.

Chart C1E, P/S Pressure Switch. Scheme 131

Chart C1E, P/S Pressure Switch. Scheme 132

Chart C4B, Ignition System Check. Scheme 133

CHART C7A - NON-ECM CONTROLLED EGR CHECK

Note. There is no text or circuit diagram with this check.

Chart C7A, Non-ECM Controlled EGR Valve Check. Scheme 134

Chart C7A, Non-ECM Controlled EGR Valve Check. Scheme 135

TORQUE CONVERTER CLUTCH (TCC) ELECTRICAL DIAGNOSIS

The purpose of automatic transmission/transaxle torque converter clutch feature is to eliminate power loss of torque converter stage when vehicle is in cruise condition. This allows convenience of automatic transmission/transaxle and fuel economy of a manual transmission. Fused battery ignition is supplied to TCC solenoid through brake switch, and transmission 3rd gear apply switch. The ECM will engages TCC by grounding circuit No. 422 to energize solenoid.

TCC will engage when vehicle speed is above 45 MPH, engine at normal operating temperature (above 158°F/70°C), throttle position sensor output not charging (indicating a steady road speed), transmission 3rd gear switch closed, and brake switch closed.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Light off confirms transmission 3rd gear apply switch is open.
2. At 30 MPH transmission/transaxle 3rd gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding diagnostic terminal with engine off should energize TCC solenoid. This test checks capability of ECM to control solenoid.
4. Solenoids are turned on or off by ECM internal electronic switches called drivers. Each driver is part of a group of 4 called quad-drivers. Failure of one can damage another driver within a set. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of ECM driver. Using an ohmmeter, check solenoid coil resistance before installing a replacement ECM.
5. Check TCC solenoid resistance. Disconnect TCC at transmission. Connect ohmmeter between transmission connector opposite harness connector terminal A and D. Raise drive wheels. Run engine in drive about 30 MPH to close 3rd gear apply switch. Replace TCC solenoid and ECM if resistance measures less than 20 ohms when switch is closed.

Chart C8, 125C Torque Converter Clutch (TCC). Scheme 136

Chart C8, 125C Torque Converter Clutch (TCC). Scheme 137

Chart C8, 125C Torque Converter Clutch (TCC) - Schematic. Scheme 138

CHART C8B - MANUAL TRANSMISSION SHIFT LIGHT

The shift light indicates best transmission shift point for maximum fuel economy. The light is controlled by ECM and is turned on by grounding terminal 19 circuit No. 456. The ECM uses MAP, distributor reference (engine speed), VSS and coolant temperature information for control.

Chart C8B, Manual Transmission Shift Light. Scheme 139

Chart C8B, Manual Transmission Shift Light. Scheme 140

CHART C10 - A/C CLUTCH CONTROL (EXCEPT "N" BODY)

ECM control of A/C clutch improves idle quality and performance by delaying clutch apply until idle air rate is increased, releasing clutch when idle speed is too low, releasing clutch at wide open throttle, and smooths cycling of compressor by providing additional fuel at instant clutch is applied. Turning on air conditioning supplies circuit No. 459 battery voltage to clutch control relay and terminal 21 of White ECM connector. After time delay of about 1/2 seconds, ECM will ground terminal 7 of Black ECM connector circuit No. 458 and close control relay.

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. Checks for low refrigerant as cause for no A/C.
2. This and following tests check for faulty A/C control relay.

Chart C10, A/C Clutch Control (Except "N" Body). Scheme 141

Chart C10, A/C Clutch Control (Except "N" Body - 1 Of 2). Scheme 142

Chart C10, A/C Clutch Control - Circuit Diagram. Scheme 143

CHART A10A - A/C CLUTCH CONTROL (EXCEPT "N" BODY)

Note. The following step numbers refer to the step numbers in the accompanying Flow Chart.

1. 3) Checks for faulty cycling switch. Solenoids and relays are turned on or off by ECM, using internal electronic switches called drivers. Each driver is part of a group of 4 called quad-drivers. Failure of one driver can damage another driver in a set. Solenoid and relay coil resistance must measure more than 20 ohms. Less resistance will cause early failure of ECM driver. Using an ohmmeter, check coil resistance of A/C relay before replacing ECM.

Chart C10A, A/C Clutch Control (Except "N" Body). Scheme 144

Chart C10A, A/C Clutch Control (Except "N" Body - 2 Of 2). Scheme 145

CHART C10 - A/C CLUTCH CONTROL ("N" BODY)

With air conditioning on, ignition voltage is supplied to compressor high side low pressure switch (identified by its Black color). If system refrigerant level is okay, low pressure switch will be closed completing circuit through closed high pressure cut-off switch (Red color) to circuit No. 459.

Circuit No. 459 supplied voltage to A/C control relay and ECM terminal 21. The ECM will delay about 1/2 seconds, then ground terminal 7 and circuit No. 458. This will close A/C relay and allow current to flow through relay and circuit No. 59 to engage compressor clutch.

Chart C10A, A/C Clutch Control Flow Chart ("N" Body). Scheme 146

CHART C10A, A/C CLUTCH CONTROL FLOW CHART ("N" BODY). Scheme 147

Chart C10A, A/C Clutch Control ("N" Body) - Ckt Diagram. Scheme 148

CHART C12 - COOLANT FAN CONTROL CKT W/A/C (EXCEPT N BODY)

Battery voltage is supplied to fan relay on terminal E and ignition to terminal C. Grounding relay terminal B will close relay and supply battery voltage to fan motor. Above 30 MPH, the ECM will remove ground from circuit No. 409. If coolant temperature and A/C pressure switches are open, fan will stop.

Chart C12, Engine Cooling Fan (Except "N" Body). Scheme 149

Chart C12, Engine Cooling Fan (Except "N" Body) Part 1. Scheme 150

Chart C12, Engine Cooling Fan (Except "N" Body) Part 2. Scheme 151

Chart C12, Engine Cooling Fan (Exc. "N" Body) - Schematic. Scheme 152

CHART C12 & 12A - COOLANT FAN CONTROL CKT W/A/C (N BODY)

Battery voltage is supplied to fan control relay terminal E and ignition terminal C. Grounding circuit No. 335 will close relay and is controlled by fan temperature switch when A/C is off or vehicle speed is above 30 MPH. When A/C control switch is on and compressor high side low pressure switch is closed, circuit No. 901 will provide ignition voltage to terminal A of A/C fan relay.

If vehicle speed is less than 30 MPH, ECM terminal 9 and circuit No. 409 are grounded. The A/C fan relay coil is grounded closing relay which in turn grounds circuit No. 335.

Chart C12A, Engine Cooling Fan (1 Of 2)("N" Body). Scheme 153

Chart C12A, Engine Cooling Fan (2 Of 2)("N" Body). Scheme 154

Chart C12A, Engine Cooling Fan. Scheme 155

Chart C12A, Engine Cooling Fan ("N" Body) - Schematic. Scheme 156

ECM Terminal Identification & Pin Voltages. Scheme 157

CCC Component Locations. Scheme 158

CCC System Wiring Diagram. Scheme 159