1.8l Turbo 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 Systems Controlled (Outputs)

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

ECM Operating Conditions Sensed (Inputs)

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
9. Crankshaft Position
10. Engine Speed
11. EGR Vacuum
12. Engine Cranking
13. Engine Detonation (ESC)
14. Exhaust Oxygen (O2)
15. Manifold Absolute Press. (MAP)
16. Mass AirFlow (MAF)
17. Manifold Air Temperature (MAF)
18. Park/Neutral Sw. Position (P/N)
19. System Voltage
20. Throttle Position (TPS)
21. Transmission Gear Position
22. Vehicle Speed (VSS)

Schematic Of Computer Command Control System. Scheme 161

Sectional View Of Mixture Control Solenoid. Note Air Bleed Above Main Metering Rod. Scheme 162

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 Field Service Mode check.
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 Field Service Mode 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 163

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 163) 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 163): 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. 1) Enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode and clear trouble codes.
2. 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. 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. 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 Field Service Mode Check.

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.

Port Fuel Injection Component Locations for 1.8L Engine. Scheme 164

The diagnostic circuit check is an organized approach for identifying a problem caused by the fuel injection system. Driver complaints fall into 3 categories: Steady "CHECK ENGINE" light, driveability problems and "engine cranks but will not run".

1. 1) A steady "CHECK ENGINE" light, with the ignition "ON" and engine stopped, confirms battery and ignition voltage to the ECM.
2. 2) Ground diagnostic test terminal by jumpering terminals "A" to "B" in the ALDL located below the instrument panel. Code 12 should flash 3 times, followed by any other trouble codes stored in memory.
3. 3) Record all stored codes except Code 12.
4. 4) With the engine running and the diagnostic terminal grounded, the ECM will respond to the O2 sensor signal voltage and use the "CHECK ENGINE" light to display this information as follows
5. A) Closed loop confirms that O2 sensor voltage is being used to control fuel delivery. Signal voltage will vary from .35-.55 volt.
6. B) Open loop confirms that O2 sensor voltage is not usable to the ECM. Signal voltage is a fixed value between .35-.55 volt. System will flash open loop for 30 seconds to 2 minutes or until O2 sensor reaches operating temperature.
7. C) O2 sensor signal voltage will be less than .35 volt.
8. D) O2 sensor signal voltage will be more than .55 volt.
9. 5) Road test of the system in the field service mode must be done at steady speeds. In this mode the following conditions may be observed and considered normal: Light "ON" too long under acceleration, light "OFF" too long under deceleration, light on too long at idle with idle below 1200 RPM.

Diagnostic Circuit Check. Scheme 165

Diagnostic Circuit Check. Scheme 166

CHART A1 - NO "CHECK ENGINE" LIGHT

"CHECK ENGINE" light should be "ON" steady when ignition is ON" and engine is "OFF". Battery voltage is supplied to the bulb, bulb is grounded by ECM through circuit 419.

1. 1) This test checks for a faulty bulb or an open control circuit 419. If test light will not light, fault can be battery supply to ECM.
2. 2) & 3) These tests check for ignition and battery contin voltages.
3. 4) Relays and solenoids are operated by the ECM, using internal switches called "Drivers". Each driver is part of a group of 4 called "Quad Drivers". Failure of any driver can damage any other driver in the set. Use an ohmmeter to check resistance of solenoids listed in chart.

Chart A1, No "CHECK ENGINE" Light. Scheme 167

Chart A1, No "CHECK ENGINE" Light. Scheme 168

Before replacing ecm, use an ohmmeter and check the resistance between solenoid and relay terminals of

1. Fan Control - Opposite Harness Connector Terminals B & C
2. A/C Relay - Opposite Harness Connector Terminals A & C
3. TCC
4. Wastegate

Replace Any Solenoid Or Relay Where Resistance Measures Less Than 20 Ohms.

CHART A2 - WON'T FLASH CODE 12 ("CHECK ENGINE" LIGHT ON)

"CHECK ENGINE" light should be "ON" steady when ignition is ON" and engine is "OFF". Battery voltage is supplied to the bulb, bulb is grounded by ECM through circuit 419.

With the diagnostic terminal grounded, the light should flash a Code 12, followed by any trouble codes stored in memory. A steady light is possibly a short to ground in circuit 419, or an open in diagnostic circuit 451.

1. 1) If the light goes "OFF" when the ECM connector is disconnected, circuit 419 is not shorted to ground. Check connector terminals for proper contact.
2. 2) This step checks for open diagnostic circuit 451.
3. 3) At this point, light wiring is okay. Problem is a faulty ECM or PROM. ECM is okay if Code 51 is stored when PROM is removed.
4. 4) Relays and solenoids are operated by the ECM, using internal switches called "Drivers". Each driver is part of a group of 4 called "Quad Drivers". Failure of any driver can damage any other driver in the set. Use an ohmmeter to check solenoids listed in chart.

Chart A2, Won't Flash Code 12 ("CHECK ENGINE" Light On). Scheme 169

Chart A2, Won't Flash Code 12 ("CHECK ENGINE" Light On). Scheme 170

CHART A3 - ENGINE CRANKS BUT WILL NOT RUN

Engine cranks but will not run, or engine cranks and dies immediately. Battery condition and engine cranking speed are okay. There is enough fuel in tank.

1. Light "ON" is a check for battery and ignition voltage to ECM.
2. No spray from injector indicates a faulty fuel system or no ECM control of injector. If light flashes while cranking, ECM control is okay. Water or foreign material can cause a no start in freezing weather. An open crank signal can cause a no start in cold weather.
3. No spark indicates an HEI problem.
4. For this test, use pressure gauge J-34730-1. Wrap a shop towel around the fuel pressure tap to absorb any fuel leakage.
5. If the TPS is sticking in the "clear flood" mode, the air/fuel ratio may be too lean to start the engine.
6. Fuel system should be considered okay. Check for possible mechanical problems.

Chart A3, Engine Cranks But Will Not Run. Scheme 171

Chart A3, Engine Cranks But Will Not Run. Scheme 172

CHART A4 - ENGINE CRANKS BUT WILL NOT RUN (CONT.)

1. 7) This test checks for 12 volts on circuit 439 to injectors.
2. 8) Check for open circuit 467 or 468 from connector to ECM.
3. 9) This test checks for reference signal from HEI distributor. ECM keeps injectors turned "OFF" until it receives a reference signal at terminal "B5".

Chart A4, Engine Cranks But Will Not Run (Cont.). Scheme 173

Chart A4, Engine Cranks But Will Not Run (Cont.). Scheme 174

CHART A5 - ENGINE CRANKS BUT WILL NOT RUN (CONT.)

The ECM will turn on the electric fuel pump when the ignition is turned "ON". The ECM will keep the pump "ON" if the engine is running or cranking (ECM is receiving reference pulses from distributor). If there are no reference pulses, the ECM turns pump OFF" within 2 seconds after key "ON". Normal pump pressure is 26-46 psi. Excess fuel is returned to the tank. The fuel pump test terminal is located in the engine compartment. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to this terminal. Improper pump pressure can cause: "cranks but won't run", Code 44, Code 45, cuts out (similar to ignition problem), poor fuel economy, lack of power, and hesitation.

1. If fuse is blown, this test will confirm a short to ground in circuit 120. To prevent mis-diagnosis, be sure fuel pump is disconnected before test.
2. This test determines if the pump is ECM controlled. ECM will turn pump "OFF" after 2 seconds of the engine not cranking or running.
3. This test turns pump "ON" if circuit 120 is okay.
4. This test checks for battery voltage at the pump relay.
5. This test checks relay ground circuit 450. See CHART A6.

Chart A5, Engine Cranks But Will Not Run (Cont.). Scheme 175

Chart A5, Engine Cranks But Will Not Run (Cont.). Scheme 176

CHART A6 - ENGINE CRANKS BUT WILL NOT RUN (CONT.)

1. 6) This test checks for ECM control of relay through circuit 465.
2. 7) The fuel pump control circuit includes an oil pressure switch, parallel to the relay. Should the relay fail, the switch will provide voltage to the pump as long as oil pressure is more than 4 psi. If the relay fails, engine crank time may be extended because pump will not run (switch will not close) until engine has oil pressure. If engine cranks slowly or switch is defective, engine may not start.
3. 8) This test checks if oil pressure switch provides voltage to pump.
4. 9) This test checks that oil pressure switch is open when engine is not running. Switch sticking closed will allow pump to run continuously and discharge battery.

Chart A6, Engine Cranks But Will Not Run (Cont.). Scheme 177

Flow Chart. Scheme 178

CHART A7 - FUEL SYSTEM DIAGNOSIS

The ECM will turn on the electric fuel pump when the ignition is turned "ON". The ECM will keep the pump "ON" if the engine is running or cranking (ECM is receiving reference pulses from distributor). If there are no reference pulses, the ECM turns pump OFF" within 2 seconds after key "ON". Normal pump pressure is 20-40 psi. Excess fuel is returned to the tank.

1. This test checks for adequate fuel delivery pressure. Pressure is controlled by spring pressure within the regulator assembly.
2. Manifold vacuum is applied to fuel pressure regulator to control fuel pressure. When engine is idling, manifold pressure is low (high vacuum) and this will lower fuel line pressure (26-32 psi). This pressure drop at idle indicates proper regulator control. Turbo boost pressure will increase fuel line pressure by approximately 1 psi for each pound of manifold boost (46 psi maximum).

Chart A7, Fuel System Diagnosis. Scheme 179

Chart A7, Fuel System Diagnosis. Scheme 180

CHART A8 - FUEL INJECTION

1. Pressure less than 30 psi can be of 2 types: Regulated pressure less than 30 psi is when the amount of fuel to injector is okay, but pressure is too low. System may run lean and set Code 44. In addition, engine may be hard starting and have poor overall performance. Restricted flow can cause pressure drop. Normally, a vehicle with a system pressure of less than 9 psi will not be driveable. If the pressure drop occurs only while driving, the engine will begin to surge then stop as pressure drops rapidly.
2. Restricting fuel return line allows pump to develop maximum pressure. Pressure should exceed 60 psi.
3. This test determines if high pressure is due to a restricted fuel return line or a pressure regulator problem.

Chart A8, Fuel Injection. Scheme 181

Chart A8, Fuel Injection. Scheme 182

CODE 13 - OPEN OXYGEN SENSOR CIRCUIT

Code 13 will set with engine at operating temperature at least 2 minutes after engine start. The ECM must see: O2 signal voltage steady, between .35-.55 volt for more than 1 minute, or see TPS signal at more than 6% (.8-1.2 volt). Possible causes of a Code 13 are a faulty O2 sensor, faulty wiring or terminals, or a faulty ECM.

1. This test 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.
3. This test simulates a lean exhaust. If the ECM and wiring are okay, the ECM will turn the "CHECK ENGINE" light off. Light will flash open loop at least 30 seconds after engine start. It is normal for the light to remain off for a longer period of time after engine start.

Code 13, Open Oxygen Sensor Circuit. Scheme 183

Code 13, Open Oxygen Sensor Circuit. Scheme 184

CODE 14 - COOLANT SENSOR SIGNAL VOLTAGE LOW

The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on circuit 410 to the sensor. When the engine is cold, sensor resistance is high and the ECM sees a high signal voltage. As the engine warms, the sensor resistance becomes less and the voltage drops. At operating temperature, voltage will measure about 1-1.5 volts at ECM terminal C-10". Code 14 will set if signal voltage indicates a coolant temperature more than 275°F (135°C) for more than 2 seconds. Possible causes of a Code 14 are: A shorted coolant sensor, faulty wiring or terminals, or a faulty ECM. Coolant temperature is used to control: Fuel delivery, engine timing (EST), knock control (ESC), idle (IAC), and converter clutch (TCC).

1. If voltage is more than 4 volts, the ECM and wiring are okay.
2. If checking resistance at the coolant sensor is difficult because of sensor location, disconnect the ECM "C-D" connector and check resistance between harness connector terminals "C-10" and "D-2".

Code 14, Coolant Sensor Signal Voltage Low. Scheme 185

Code 14, Coolant Sensor Signal Voltage Low. Scheme 186

CODE 15 - COOLANT SENSOR SIGNAL VOLTAGE HIGH

The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on circuit 410 to the sensor. When the engine is cold, sensor resistance is high and the ECM sees a high signal voltage. As the engine warms, the sensor resistance becomes less and the voltage drops. At operating temperature, voltage will measure about 1-1.5 volts at ECM term. C-10". Code 15 will set if signal voltage indicates a coolant temperature less than -31°F (-35°C) for more than 4 seconds. Possible causes of a Code 15 are: An open coolant sensor, faulty wiring or terminals, or a faulty ECM. Coolant temperature is used to control: Fuel delivery, engine timing (EST), knock control (ESC), idle (IAC), and converter clutch (TCC).

1. If voltage is more than 4 volts, the ECM and wiring are okay.
2. If checking resistance at the coolant sensor is difficult because of sensor location, disconnect the ECM "C-D" connector and check resistance between harness connector terminals "C-10" and "D-2".

Code 15, Coolant Sensor Signal Voltage High. Scheme 187

Code 15, Coolant Sensor Signal Voltage High. Scheme 188

CODE 21 - TPS SIGNAL VOLTAGE HIGH

The Throttle Position Sensor (TPS) provides a voltage signal that changes with the position of the throttle valve. Signal voltage will vary from idle (.5 volt) to wide open throttle (4.5 volts). Code 21 will set if

1. Engine is running and TPS voltage is greater than 2.5 volts for 8 seconds with engine speed less than 1600 RPM.
2. Code 33 or 34 are not present at start-up.
3. MAP is less than 10 psi (no load condition).

Possible causes of a Code 21 are faulty TPS, faulty wiring or terminals, a faulty ECM.

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

Code 21, TPS Signal Voltage High. Scheme 189

Code 21, TPS Signal Voltage High. Scheme 190

CODE 22 - TPS SIGNAL VOLTAGE LOW

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the position of the throttle valve. Signal voltage will vary from idle (.5 volt) to wide open throttle (4.5 volts). Code 21 will set if engine is running and TPS voltage is less than .1 volt for 8 seconds with engine speed less than 1600 RPM.

Possible causes of a Code 22 are faulty TPS, faulty wiring or terminals, a faulty ECM.

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

Code 22, TPS Signal Voltage Low. Scheme 191

Code 22, TPS Signal Voltage Low. Scheme 192

CODE 23 - MAT SENSOR SIGNAL VOLTAGE HIGH

The Manifold Air Temperature (MAT) sensor uses a thermistor to control signal voltage to the ECM. The ECM applies a voltage on circuit 472 to the sensor. When manifold air is cold, the sensor resistance is high and the ECM will set a high signal voltage. As the incoming air warms, the sensor resistance becomes less, and the voltage drops. At engine operating temperature, the voltage will measure about 1-2 volts at ECM term. "C-12".

Code 23 will set if

1. Signal voltage indicates a manifold air temperature less than -31°F (-35°C) for 5 seconds during a boost condition.
2. Time since engine start is more than 1 minute.

Possible causes of a Code 23 are an open MAT sensor, faulty wiring or terminals, or a faulty ECM. MAT is one of the inputs used to control fuel delivery, spark timing (EST), and idle (IAC).

1. If voltage is more than 4 volts, ECM and wiring are okay.
2. If location of sensor makes it hard to check, disconnect ECM connectors and check resistance between terms. "C-12" and "A11".

Code 23, MAT Sensor Signal Voltage High. Scheme 193

Code 23, MAT Sensor Signal Voltage High. Scheme 194

CODE 24 - VEHICLE SPEED SENSOR (VSS) (INTEGRAL BUFFER)

The ECM supplies a current limited 12 volt signal on circuit 437. The VSS located in the I.P. cluster will sense the speedometer rotating element and furnish this information to the buffer as a pulsed" signal (2 pulses per cable revolution or 2002 per mile). The buffer assembly will switch circuit 437 to ground for each pulse received. The ECM uses the time between pulses to determine vehicle speed.

Code 24 is set by the following

1. Circuit 437 voltage is constant for 4-10 seconds.
2. Engine speed is 1500-4400 RPM
3. Park/Neutral switch indicates transmission is in Drive range.
4. Low MAP (high vacuum) indicating an engine deceleration.

Loss of VSS will affect converter clutch (TCC) and idle (IAC), and fan control will not shut off above 30 MPH with A/C on.

1. This test checks if there is a VSS signal to the ECM while turning drive wheel. Voltage should vary from less than 3 volts to more than 6 volts with less variation as wheel speed increases.

Code 24, Vehicle Speed Sensor (VSS) (Integral Buffer). Scheme 195

Code 24, Vehicle Speed Sensor (VSS) (Integral Buffer). Scheme 196

CODE 25 - MAT SENSOR SIGNAL VOLTAGE LOW

The Manifold Air Temperature (MAT) sensor uses a thermistor to control signal voltage to the ECM. The ECM applies a voltage on circuit 472 to the sensor. When manifold air is cold, the sensor resistance is high and the ECM will set a high signal voltage. As the incoming air warms, the sensor resistance becomes less and the voltage drops. At engine operating temperature, the voltage will measure about 1-2 volts at ECM terminal "C-12".

Code 25 will set if signal voltage indicates a manifold air temperature greater than 275°F (135°C) for more than 2 seconds. Possible causes of a code 25 are faulty wiring or terminals, circuit 472 shorted to ground, shorted MAT sensor, or faulty ECM. MAT is one of the inputs used to control fuel delivery, spark timing (EST), knock control (ESC), and idle (IAC).

1. If voltage is more than 4 volts, ECM and wiring are okay.
2. If checking resistance at the manifold air sensor is difficult because of sensor location, disconnect the ECM connectors and check resistance between harness connector terminals "C-12" and "A11".

Code 25, MAT Sensor Signal Voltage Low. Scheme 197

Code 25, MAT Sensor Signal Voltage Low. Scheme 198

CODE 31 - WASTEGATE OVERBOOST & FUNCTIONAL CHECK

Code 31 will set when the manifold pressure exceeds about 15 pounds of boost for 2 seconds and Code 33 has not been previously set. Code 31 will set and the "CHECK ENGINE" light will stay "ON" only while overboost exists. The light will stay "ON" for 10 seconds after the condition exists and then go "OFF". An overboost condition could be caused by circuit 435 shorted to ground, wastegate actuator or wastegate sticking closed, a control valve stuck in the closed position, a cut or pinched hose, or a faulty ECM. An underboost condition could be caused by a wastegate actuator or wastegate sticking open, no ignition feed to control valve or an open wire to ECM, or a faulty ECM.

1. With key "OFF", the control valve solenoid is open and should allow pressure to be applied to wastegate actuator.
2. After 15 psi is applied to valve and the pressure source is removed, the actuator should slowly move back and close wastegate. If pressure does not bleed off, the vent in the control valve solenoid could be plugged.
3. With key "ON" and diagnostic terminal grounded, control valve solenoid should be energized. This closes off the manifold to the wastegate actuator.
4. This test checks electrical control portion of the system. Key "ON" and engine not running, solenoid should not be energized. Key ON" and diagnostic terminal grounded, solenoid should be energized.

Code 31, Wastegate Overboost & Functional Check. Scheme 199

Code 31, Wastegate Overboost & Functional Check. Scheme 200

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 signal voltage that will vary from 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 value and use the TPS sensor to control fuel delivery. Code 33 will set when signal voltage is too high for more than 8 seconds. Possible causes of a Code 33 are a faulty MAP sensor, faulty wiring or terminals, or a faulty ECM. Disconnect MAP sensor and system will go to back-up mode. If misfire or idle condition remains, MAP sensor is okay.

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.
3. If circuit 432 is shorted to voltage, check turbo boost gauge unit.

Code 33, MAP Sensor Signal Voltage High. Scheme 201

Code 33, MAP Sensor Signal Voltage High. Scheme 202

CODE 34 - MAP SENSOR SIGNAL VOLTAGE LOW

The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as signal voltage that will vary from 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 value and use the TPS sensor to control fuel delivery. Code 34 will set when signal voltage is too low and ignition is turned "ON". Possible causes of a Code 34 are a faulty MAP sensor, faulty wiring or terminals, or a faulty ECM. Engine misfire or unstable idle may set a Code 33. Disconnect MAP sensor and system will go to back-up mode. If misfire or idle condition remains, MAP sensor is okay.

1. This test confirms Code 34, and that fault is present.
2. If the ECM recognizes and sets Code 33, low MAP signal, the ECM and wiring are okay.
3. If circuit 432 is shorted to ground, check turbo boost gauge unit.

Code 34, MAP Sensor Signal Voltage Low. Scheme 203

Code 34, MAP Sensor Signal Voltage Low. Scheme 204

CODE 42 - ELECTRONIC SPARK TIMING (EST)

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

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. An EST circuit 423 shorted to ground will read less than 500 ohms.
3. As the test light voltage touches terminal "D5", the module should switch causing the ohmmeter to "overrange" if the meter is in the 1000-2000 ohm position. Selecting a higher ohms position will indicate above 5000 ohms. It is only important that the module switched".
4. If the module did not switch, this step will check for EST circuit 423 shorted to ground, an open by-pass circuit 424, or a faulty ignition module connection or module.
5. This test confirms that Code 42 is a faulty ECM and not an intermittent in circuits 423 or 424.

Code 42, Electronic Spark Timing (EST). Scheme 205

Code 42, Electronic Spark Timing (EST). Scheme 206

CODE 43 - ELECTRONIC SPARK CONTROL

Code 43 indicates the ECM has seen low voltage at circuit 457, terminal "B7" in the ECM "AB" connector for longer than 4 seconds with the engine running. This voltage drops when the ESC module shuts off because it receives a knock signal.

1. The ESC module supplies voltage to the ECM. It should always be over 6 volts unless the system is sensing engine detonation.
2. This test checks for intermittent ESC operation. If the voltage is now over 6 volts, it is faulty ESC terminal "C" connection or ESC module.

Code 43, Electronic Spark Control. Scheme 207

Code 43, Electronic Spark Control. Scheme 208

CODE 44 - LEAN EXHAUST INDICATION

Code 44 indicates that the ECM has seen O2 sensor voltage at ECM terminal "D7") lower than .2 volts for 50 seconds or more, 1 minute after engine start. The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". The O2 sensor varies the voltage from 1 volt (rich indication) to .10 volt (lean indication). An open sensor circuit or a bad sensor causes open loop operation.

1. This test allows the ECM to confirm either open or closed loop operation.
2. A light out or "open loop" indicates presence of a fault. Disconnecting the O2 sensor will raise the signal voltage above .2 volt. If the ECM and wiring are good, the ECM should recognize the higher voltage, .35 to .55 volt, and flash "open loop" when the engine is started.
3. Code 44 is most likely the result of: Open circuit 413, fuel pressure too low, contaminated fuel, O2 sensor wire grounded, EGR not opening, or MAP sensor giving false low reading. If these 6 systems are found to be operating, O2 sensor is faulty.

Code 44, Lean Exhaust Indication. Scheme 209

Code 44, Lean Exhaust Indication. Scheme 210

CODE 45 - RICH EXHAUST INDICATION

Code 45 indicates that the ECM has seen O2 sensor voltage at ECM terminal "D7") lower than .7 volts for longer than 30 seconds, 1 minute after engine starts. The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". The O2 sensor varies the voltage from 1 volt (rich indication) to .10 volt (lean indication). An open sensor circuit or a bad sensor causes open loop operation.

1. This test allows the ECM to confirm either open or closed loop operation.
2. A steady light or open loop indicates presence of a fault. Grounding circuit 412 causes a low O2 signal voltage. If the ECM and wiring are good, the ECM should recognize the low voltage and confirm the lean signal by turning off the light for at least 15 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, coolant sensor, MAP sensor, and TPS.

Code 45, Rich Exhaust Indication. Scheme 211

Code 45, Rich Exhaust Indication. Scheme 212

CODE 51 - PROM FAILURE

Check that all pins are fully inserted in the socket. If okay, clear memory and recheck. If CODE 51 resets, replace ECM.

Code 52, CALPAC Missing. Scheme 213

Codes 51, 52 & 55. Scheme 214

CODE 55 - REPLACE ECM

Clear codes and confirm "CLOSED LOOP" operation and 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 215

Flow Chart C1A, Park/Neutral Switch. Scheme 216

Flow Chart C1A, Park/Neutral Switch. Scheme 217

Flow Chart C1B, Crank Signal. Scheme 218

Flow Chart C1B, Crank Signal. Scheme 219

Flow Chart C1E, Power Steering Pressure Switch (PSPS) Check. Scheme 220

Flow Chart C1E, Power Steering Pressure Switch (PSPS) Check. Scheme 221

Flow Chart C1F, MAP Output Check. Scheme 222

Flow Chart C1F, MAP Output Check. Scheme 223

Flow Chart C2C, Idle Air Control (IAC). Scheme 224

Flow Chart C2C, Idle Air Control (IAC). Scheme 225

Flow Chart C5, Electronic Spark Control (ESC) System Check. Scheme 226

Flow Chart C5, Electronic Spark Control (ESC) System Check (1 Of 2). Scheme 227

Flow Chart C5, Electronic Spark Control (ESC) System Check (2 Of 2). Scheme 228

Flow Chart C8, TCC Electrical Diagnosis. Scheme 229

Flow Chart C8, TCC Electrical Diagnosis. Scheme 230

Flow Chart C10, A/C Clutch Control. Scheme 231

Flow Chart C10, A/C Clutch Control. Scheme 232

Flow Chart C10A, A/C Clutch Control (Cont.). Scheme 233

Flow Chart C10A, A/C Clutch Control (Cont.). Scheme 234

Flow Chart C12 (1 of 3), Coolant Fan Control Circuit. Scheme 235

Flow Chart C12 (2 of 3), Coolant Fan Control Circuit. Scheme 236

Flow Chart C12 (3 of 3), Coolant Fan Control Circuit. Scheme 237

Flow Chart C12 (2 of 4), Coolant Fan Control Circuit. Scheme 238

Flow Chart C12 (3 of 4), Coolant Fan Control Circuit. Scheme 239

Flow Chart C12 (4 of 4), Coolant Fan Control Circuit. Scheme 240

Port Fuel Injection ECM Terminal ID for 1.8L Engine. Scheme 241

1.8L Engine Port Fuel Injection CCC Wiring Diagram. Scheme 242