3.0l/3.8l Pfi Tests W/codes Buick Electra Estate Wagon

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
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 Air Flow (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)

ECM OPERATING SYSTEMS CONTROLLED

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

Schematic of Computer Command Control System. Scheme 259

Sectional View of Mixture Control Solenoid Note air bleed above main metering rod. Scheme 260

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 261

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 261) 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 261): 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 System Performance Check (carbureted engines) or the Field Service Mode (EFI engines) 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).

SYSTEM PERFORMANCE CHECK (CARBURETED MODELS ONLY)

1. This check verifies that CCC system is functioning correctly. This check should always be made after any repair on CCC system.
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. On engines equipped with Varajet carburetors (E2SE Model), remove bowl vent line at carburetor and plug hose at carburetor during check and reconnect it after the check is complete.
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.

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.

FUEL SYSTEM PRESSURE TEST

Note. Trouble shooting and diagnosis of the fuel system should begin with determining fuel injection system pressure. Before performing any test on the fuel system, pressure must be released from the system.

1. Remove "FUEL PUMP" fuse from fuse block. Crank engine. Engine will start and run until fuel supply remaining in fuel lines is used. Engage the starter again for about 3 seconds to ensure that all fuel is out of lines.
2. Remove air cleaner and plug thermal vacuum port on throttle body. Remove steel fuel line from between front and rear throttle body units. When removing fuel line, always use 2 wrenches. Install fuel pressure gauge (J-29658 or equivalent) between throttle body units.
3. Reinstall "FUEL PUMP" fuse in fuse block. Start engine and observe fuel pressure reading. If fuel pressure is not between 9 and 13 psi (.6-.9 kg/cm 2 ), proceed to Fuel System Diagnosis chart. If fuel pressure is okay, proceed to step 4).
4. Depressurize fuel system as described in step 1). Remove fuel pressure gauge and reinstall steel fuel line between throttle bodies. Reinstall "FUEL PUMP" fuse in fuse block. Start engine and watch for fuel system leaks. Remove plug from throttle body thermal vacuum port and reinstall air cleaner.

USING THE DIAGNOSTIC CIRCUIT CHECK

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 WON'T 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) 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 volts.
6. B) Open loop confirms that O2 sensor voltage is unusable to the ECM. Signal voltage is a fixed value between .35-.55 volts. 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 262

CHART A1 - NO "CHECK ENGINE SOON" 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 continuous voltages.
3. 4) Relays and switches 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 Schematic, No "CHECK ENGINE" Light (All Engines). Scheme 263

Chart A1, No "CHECK ENGINE" Light (All Engines). Scheme 264

CHART A2 - NO CODE 12 "CHECK ENGINE SOON" 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. 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. This step checks for open diagnostic circuit 451.
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. Relays and switches 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 Schematic, Won't Flash Code 12, ("CHECK ENGINE" Light On) (All Engines). Scheme 265

Chart A2, Won't Flash Code 12, ("CHECK ENGINE" Light On) (All Engines). Scheme 266

CHART A3 - ENGINE CRANKS BUT WILL NOT RUN (3.0L)

Engine cranks but won't run, or engine starts and dies immediately. Battery condition and engine cranking speed are okay. There is enough fuel in tank.

Circuit Description (3.0L VIN N)

This engine is equipped with a distributorless ignition system called Computer Controlled Coil Ignition (C3I). The EST and Bypass circuits operate in the same manner as in an HEI system.

Note. Test numbers below refer to the circled numbers on the diagnostic chart.

1. A "Check Engine" light "ON" is a basic check for ignition and battery supply to the Electronic Control Module (ECM).
2. Removing the fuel pump fuse at this point will prevent engine flooding during tests made, if an injector is stuck open. Checks to see if the ECm is controlling the fuel injectors. A blinking test light at this point indicates the ECM is controling the injectors and that ignition reference signal to the ECM is good.
3. Checks to see if problem is fuel or ignition related.
4. Checks to see if fuel pump and relay are operating correctly. Fuel pump should run for only 2 seconds after ignition "ON".
5. Checks to see if ECM is receiving reference signal from ignition system.

DIAGNOSTIC AIDS.

Check For

1. Open coolant sensor.
2. EGR sticking open.
3. TPS binding or sticking in wide open throttle position.
4. Water or foreign material in fuel.
5. A defective MAF Sensor may cause a no start or a stall after start. To determine if the sensor is causing the problem, disconnect it. The ECM will then use a default value for the sensor, and if the condition is correct and connections are OK, replace the sensor.

Ignition System Schematic (3.0L, VIN N). Scheme 267

Flow Chart A3, Cranks But Won't Run (3.0L, VIN N). Scheme 268

Circuit Description For Steps 1-6 (Chart 1 Of 3 - 3.0L VIN L)

The C(3)I ignition system uses a waste spark method of spark distribution. In this type of ignition system, the ignition module triggers the 1/4 coil pair, resulting in the Nos. 1 and 4 spark plug firing at the same time. The No. 1 cylinder is on the compression stroke while the No. 4 cylinder is on it's exhaust stroke, resulting in a lower energy requirement to fire the No. 4 spark plug. This leaves the remaining high voltage to fire the No. 1 spark plug.

The simultaneous fuel injection type of delivery system uses 2 injector driver circuits in parallel, to activate the 6 fuel injectors. The ECM activates all 6 of the injectors simultaneously.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. (Scheme 263)-7.

1. This step verifies that the "SES" light is operational, and TPS, and coolant sensor signals are normal. A blinking injector test light verifies that the ECM is monitoring the C(3)I reference signal and attempting to activate the injectors.
2. Both the "SYNC-PULSE" and Crank signals have been verified as functioning properly, as is evidenced by the blinking injector test light. A fuel pressure test, at this point, will separate the diagnostic path into either a fuel related fault or ignition system malfunction.
3. The 3-terminal injector harness connector must be disconnected to avoid flooding or fouling spark plugs. By testing for spark at plug leads 1, 3, and 5, each ignition coil's ability to produce 25,000 volts is verified.
4. By testing the problem coil's control circuit with a test light, a determination can be made whether the problem coil is faulty or if the module's internal driver for that specific coil is at fault.
5. An injector with a resistance of less than 10 ohms must be replaced due to a short.
6. This step tests for battery voltage at circuit No. 939. If voltage is present, the "LIGHT OFF" test result was caused by no activation pulse reaching the injector connector from the ECM.

Note. In the following circuit schematic, circuit numbers and wire colors may vary between vehicles. However, pin numbers and components represented are accurate.

Ignition System Schematic (3.0L, VIN L). Scheme 269

Chart A3 (1 of 4). Scheme 270

Chart A3 (2 of 4). Scheme 271

Ckt Description For Steps 7-11 (Chart 2 Of 3 - 3.0L VIN L)

For synchronization of spark plug firing, a "SYNCH-PULSE" is created by the combination sensor "HALL EFFECT" switch. The sensor sends the "SYNC-PULSE" signal to the ignition module when cylinders No. 1 and 4 are 25° ATDC on the compression stroke. This signal is used to start the correct firing sequence with the No. 3/6 ignition coil.

The crank signal portion of the combination sensor sends a signal to the ignition module for coil activation and then to the ECM for reference RPM and crankshaft position. There are 3 windows in a disc (interrupter) which is mounted to the harmonic balancer. As these windows pass through the slot in the sensor, the next coil is triggered.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. (Scheme 263)-7.

1. 7) Verifies ignition feed voltage at terminal "P" of the C(3)I ignition module. Less than battery voltage would be an indication of a circuit No. 439 fault.
2. 8) The test light to 12 volts simulates a reference signal to the ECM which will result in an injector test light blink. This validates circuit No. 430, the ECM, and the injector test light blink.
3. 9) Jumping the combination sensor harness terminals "B" and "C" together simulates a "SYNCH-PULSE" signal being transmitted to the C(3)I module. Then, by repeatedly jumping the combination sensor harness terminals "B" and "D" together, a crank signal is simulated, which should result in the injector test light blinking.
4. 10) Verifies a proper cam signal circuit voltage of 6-9 volts and a good ground from the C(3)I module to terminal "B" of the sensor connector.
5. 11) Determines if incorrect voltage reading was due to a fault in circuit No. 972, an open in circuit No. 952, or a faulty C(3)I module. If the C(3)I module was faulty, also verify that circuit 453 to the ECM terminal "B3" is not open.

From Chart A-3 (3 Of 4). Scheme 272

Ckt Description For Steps 12 & 13 (Chart 3 Of 3 - 3.0L VIN L)

For synchronization of spark plug firing, a "SYNCH-PULSE" is created by the combination sensor "HALL EFFECT" switch. The sensor sends the "SYNC-PULSE" signal to the ignition module when cylinders No. 1 and 4 are 25° ATDC on the compression stroke. This signal is used to start the correct firing sequence with the No. 3/6 ignition coil.

The crank signal portion of the combination sensor sends a signal to the ignition module for coil activation and then to the ECM for reference RPM and crankshaft position. There are 3 windows in a disc (interrupter) which is mounted to the harmonic balancer. As these windows pass through the slot in the sensor, the next coil is triggered.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. (Scheme 263)-8.

1. 12) This step verifies a proper crank signal circuit voltage of 7-9 volts and a good ground from the C(3)I module to terminal "B" of the sensor connector.
2. 13) Determines if incorrect voltage reading was due to a fault in circuit No. 971, an open in circuit No. 952, or a faulty C(3)I module.

From Chart A-3 (4 Of 4). Scheme 273

Eng. Cranks But Won't Run (3.8L VIN 3 & VIN B W/Type I Ign. System)

Engine cranks but won't run, or engine starts and dies immediately. Battery condition and engine cranking speed are okay. There is enough fuel in tank.

Ignition System Identification

To identify whether you have "TYPE I" or "TYPE II" ignition system, compare the position of the coil towers on the vehicle with those displayed at the top, right corner of the diagnostic chart. The "TYPE I" ignition system has 3 coil towers on each side of the engine and the "TYPE II" system has all 6 coil towers on one side.

Circuit Description For Steps 1-6 (Chart 1 OF 3 - Type I)

The C(3)I ignition system uses a waste spark method of spark distribution. In this type of ignition system, the ignition module triggers the 1/4 coil pair, resulting in the Nos. 1 and 4 spark plug firing at the same time. The No. 1 cylinder is on the compression stroke while the No. 4 cylinder is on it's exhaust stroke, resulting in a lower energy requirement to fire the No. 4 spark plug. This leaves the remaining high voltage to fire the No. 1 spark plug.

The sequential fuel injection type of delivery system uses 6 separate injector driver circuits to activate the 6 fuel injectors. During engine cranking, the ECM activates all 6 of the injectors simultaneously. After a calibrated engine RPM is reached, and a good cam signal has been received by the ECM, the injection mode reverts to sequential injection.

Note. Test numbers below refer to the circled numbers on the diagnostic chart.

1. This step verifies that the "SES" light is operational, and TPS, and coolant sensor signals are normal. A blinking injector test light verifies that the ECM is monitoring the C(3)I reference signal and attempting to activate the injectors.
2. Both the Cam and Crank sensors have been verified as functioning properly, as is evidenced by the blinking injector test light. A fuel pressure test, at this point, will separate the diagnostic path into either a fuel related fault or ignition system malfunction.
3. The 8-terminal injector harness connector must be disconnected to avoid flooding or fouling spark plugs. By testing for spark at plug leads 1, 3, and 5, each ignition coil's ability to produce 25,000 volts is verified.
4. By testing the problem coil's control circuit with a test light, a determination can be made whether the problem coil is faulty or if the module's internal driver for that specific coil is at fault.
5. An injector with a resistance of less than 10 ohms must be replaced due to a short.
6. This step tests for battery voltage at circuit No. 639 and/or circuit No. 939. If voltage is present, the "LIGHT OFF" test result was caused by no activation pulse reaching the injector connector from the ECM.

Note. In the following circuit schematic, circuit numbers and wire colors may vary between vehicles. However, pin numbers and components represented are accurate.

Ignition System Schematic (3.8L, Type I Ignition System). Scheme 274

Flow Chart A3 (1 of 3), Cranks But Won't Run (3.8L, Type I Ign. System). Scheme 275

Circuit Description For Steps 7-11 (Chart 2 Of 3 - Type I)

For timing of spark plug firing, a cam sensor "HALL EFFECT" switch is used. The cam sensor sends a signal "SYNC-PULSE" to the ignition module when cylinder No. 1 is 25° ATDC on the compression stroke. This signal is used to start the correct firing sequence and to enable sequential fuel injection. The engine will continue to run if the cam signal to the ignition module (circuit No. 633) is lost, however, it will not restart if shut down and will set a Code 41.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. (Scheme 276)and (Scheme 277).

1. 7) Verifies ignition feed voltage at terminal "M" of the C(3)I ignition module. Less than battery voltage would be an indication of a circuit No. 939 fault.
2. 8) The test light to 12 volts simulates a reference signal to the ECM which will result in an injector test light blink. This validates circuit No. 430, the ECM, and the injector test light blink.
3. 9) If the cam sensor signal circuit terminal "A" is jumped to the ground circuit terminal "B", the response should be an injector test light blink. This is a result of this artificial cam signal being transmitted through the C(3)I module to the ECM terminal "A11" and the ECM activating the injector driver circuit.
4. 10) Verifies a proper cam signal circuit voltage of 6-9 volts and a good ground from the C(3)I module to terminal "B" of the sensor connector.
5. 11) Determines if incorrect voltage reading was due to a fault in circuit No. 633, an open in circuit No. 632, or a faulty C(3)I module.

Flow Chart A3 (2 of 3), Cranks But Won't Run (3.8L, Type I Ign. System). Scheme 276

Circuit Description For Steps 12-14 (Chart 3 Of 3 - Type I)

For timing of spark plug firing, a cam sensor "HALL EFFECT" switch is used. The cam sensor sends a signal "SYNC-PULSE" to the ignition module when cylinder No. 1 is 25° ATDC on the compression stroke. This signal is used to start the correct firing sequence and to enable sequential fuel injection. The engine will continue to run if the cam signal to the ignition module (circuit No. 633) is lost, however, it will not restart if shut down and will set a Code 41.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. (Scheme 275)

1. 12) Jumping the cam sensor harness terminals "A" and "B" together simulates a cam signal to the C(3)I module. Then by repeatedly jumping the crank sensor harness terminals "B" and "C" together, a crank signal is simulated which should result in the injector test light blinking.
2. 13) This step verifies a proper crank signal circuit voltage of 6-9 volts and a good ground from the C(3)I module to terminal "B" of the sensor connector.
3. 14) Determines if incorrect voltage reading was due to a fault in circuit No. 643, an open in circuit No. 642, or a faulty C(3)I module.

Flow Chart A3 (3 of 3), Cranks But Won't Run (3.8L, Type I Ign. System). Scheme 277

Eng. Cranks But Won't Run (3.8L VIN 3 & VIN B W/Type II Ign. System)

Engine cranks but won't run, or engine starts and dies immediately. Battery condition and engine cranking speed are okay. There is enough fuel in tank.

To identify whether you have "TYPE I" or "TYPE II" ignition system, compare the position of the coil towers on the vehicle with those displayed at the top, right corner of the diagnostic chart. The "TYPE I" ignition system has 3 coil towers on each side of the engine and the "TYPE II" system has all 6 coil towers on one side.

Circuit Description For Steps 1-6 (Chart 1 Of 3 - Type II)

The C(3)I ignition system uses a waste spark method of spark distribution. In this type of ignition system, the ignition module triggers the 1/4 coil pair, resulting in the Nos. 1 and 4 spark plug firing at the same time. The No. 1 cylinder is on the compression stroke while the No. 4 cylinder is on it's exhaust stroke, resulting in a lower energy requirement to fire the No. 4 spark plug. This leaves the remaining high voltage to fire the No. 1 spark plug.

The sequential fuel injection type of delivery system uses 6 separate injector driver circuits to activate the 6 fuel injectors. During engine cranking, the ECM activates all 6 of the injectors simultaneously. After a calibrated engine RPM is reached, and a good cam signal has been received by the ECM, the injection mode reverts to sequential injection.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. (Scheme 276)and (Scheme 277).

1. This step verifies that the "SES" light is operational, and TPS, and coolant sensor signals are normal. A blinking injector test light verifies that the ECM is monitoring the C(3)I reference signal and attempting to activate the injectors.
2. Both the Cam and Crank sensors have been verified as functioning properly, as is evidenced by the blinking injector test light. A fuel pressure test, at this point, will separate the diagnostic path into either a fuel related fault or ignition system malfunction.
3. The 8-terminal injector harness connector must be disconnected to avoid flooding or fouling spark plugs. By testing for spark at plug leads 1, 3, and 5, each ignition coil's ability to produce 25,000 volts is verified.
4. By switching the problem coil with a working one, a determination can be made whether the problem coil is faulty or if the module's internal driver for that specific coil is at fault.
5. An injector with a resistance of less than 10 ohms must be replaced due to a short.
6. This step tests for battery voltage at circuit No. 639 and/or circuit No. 939. If voltage is present, the "LIGHT OFF" test result was caused by no activation pulse reaching the injector connector from the ECM.

Note. In the following circuit schematic, circuit numbers and wire colors may vary between vehicles. However, pin numbers and components represented are accurate.

Note. Fuel system is under pressure. To avoid fuel spillage, refer to field service procedures for testing or repairs that require disassembly of fuel lines or fittings.

Chart A3 (1 of 4). Scheme 278

Chart A3 (2 of 4). Scheme 279

Circuit Description For Steps 7-11 (Chart 2 Of 3 - Type II)

For timing of spark plug firing, a cam sensor "HALL EFFECT" switch is used. The cam sensor sends a signal "SYNC-PULSE" to the ignition module when cylinder No. 1 is 25° ATDC on the compression stroke. This signal is used to start the correct firing sequence and to enable sequential fuel injection. The engine will continue to run if the cam signal to the ignition module (circuit No. 633) is lost, however, it will not restart if shut down and will set a Code 41.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. (Scheme 276)and see scheme 20.

1. 7) Verifies ignition feed voltage at terminal "M" of the C(3)I ignition module. Less than battery voltage would be an indication of a circuit No. 939 fault.
2. 8) The test light to 12 volts simulates a reference signal to the ECM which will result in an injector test light blink. This validates circuit No. 430, the ECM, and the injector test light blink.
3. 9) If the cam sensor signal circuit terminal "A" is jumped to the ground circuit terminal "B", the response should be an injector test light blink. This is a result of this artificial cam signal being transmitted through the C(3)I module to the ECM terminal "A11" and the ECM activating the injector driver circuit.
4. 10) Verifies a proper cam signal circuit voltage of 6-9 volts and a good ground from the C(3)I module to terminal "B" of the sensor connector.
5. 11) Determines if incorrect voltage reading was due to a fault in circuit No. 633, an open in circuit No. 632, or a faulty C(3)I module.

From Chart A-3 (3 Of 4). Scheme 280

Circuit Description For Steps 12-14 (Chart 3 Of 3 - Type II)

For timing of spark plug firing, a cam sensor "HALL EFFECT" switch is used. The cam sensor sends a signal "SYNC-PULSE" to the ignition module when cylinder No. 1 is 25° ATDC on the compression stroke. This signal is used to start the correct firing sequence and to enable sequential fuel injection. The engine will continue to run if the cam signal to the ignition module (circuit No. 633) is lost, however, it will not restart if shut down and will set a Code 41.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. (Scheme 276)

1. 12) Jumping the cam sensor harness terminals "A" and "B" together simulates a cam signal to the C(3)I module. Then by repeatedly jumping the crank sensor harness terminals "B" and "C" together, a crank signal is simulated which should result in the injector test light blinking.
2. 13) This step verifies a proper crank signal circuit voltage of 6-9 volts and a good ground from the C(3)I module to terminal "B" of the sensor connector.
3. 14) Determines if incorrect voltage reading was due to a fault in circuit No. 643, an open in circuit No. 642, or a faulty C(3)I module.

From Chart A-3 (4 Of 4). Scheme 281

Chart A3 Schematic, Engine Cranks But Will Not Run (3.8L W/HEI). Scheme 282

Test Conditions

Engine cranks but won't run, or engine starts and dies immediately. Battery condition and engine cranking speed are okay. There is enough fuel in tank.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. See below.

1. A SERVICE ENGINE SOON light ON is a basic check for ignition and battery supply to the Electronic Control Module (ECM).
2. No fuel spray from injector indicates a faulty fuel system or no ECM control of injector. If the test light blinks while cranking, then ECM control should be considered okay. Be sure test light makes good contact between connector terminals during test. The light may a little dim when blinking. This is due to current draw of test light. Brightness of blinking is not important. Test light bulb should be No. 1847 or equivalent.
3. Secondary voltage (spark) is checked using an ST-125. No spark indicates a basic HEI problem. If spark is okay the following checks should be made.
4. Use pressure gauge (part number J-34730-1 or equivalent). Wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gauge.

Throttle Position Sensor (TPS): If the sensor is sticking or binding in the wide open throttle position, the ECM will be in the "Clear Flood" mode. The air/fuel ratio will be 18:1 to 20:1, and this may be too lean to start a cold engine. Water or foreign material can cause a no start during freezing weather. The engine may start after 5 or 6 minutes in a heated shop. The problem may not reoccur until an overnight park in freezing temperatures.

An EGR sticking open can cause a high air/fuel ratio during cranking. Unless engine enters "Clear Flood" at the first indication of a flooding condition, it can result in a no-start.

A defective MAF Sensor may cause a no-start or a stall after start. To determine if the sensor is causing the problem, disconnect it. The ECM will then use a default value for the sensor, and if the condition is corrected and the connections are okay, replace the sensor.

Chart A3 - 3.8L Non-Turbo W/HEI. Scheme 283

Engine cranks but won't run, or engine starts 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. Remove fuel pump fuse to prevent flooding if an injector is stuck open. This test checks to see if ECM is controlling injectors. Blinking test light indicates ECM is controlling injectors and the ignition reference signal to ECM is good.
3. This test checks to see if problem is fuel or ignition related.
4. This test checks fuel pump and relay. Fuel pump should run for only 2 seconds after ignition is turned "ON".
5. This test checks if ECM is receiving reference signal from ignition system.
6. Connect a timing light and note spark timing while cranking. Should be 10-15° BTDC. If timing mark is not visible while cranking, remove cam sensor cover and check for loose interrupter cup. If cup is not loose, set sensor timing. If timing mark is still not visible, internal camshaft timing problem is indicated.

Chart A3 - 3.8L Turbo. Scheme 284

CHART A4 - ENGINE CRANKS BUT WILL NOT RUN (3.8L)

1. This test checks for 12 volts on circuit 439 to injectors.
2. This test checks circuit 841 and 844 from injectors to ECM.
3. This test checks for reference signal from HEI distributor. The ECM keeps fuel injectors turned off until it receives the reference signal at term. "B5".
4. This test checks faulty HEI circuit.

From Chart A-3. Scheme 285

CHART A5 - ENGINE CRANKS BUT WILL NOT RUN (3.0L & 3.8L)

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 Schematic, Eng. Cranks But Will Not Run (3.0L & 3.8L). Scheme 286

Chart A5 Continued From Chart A-3. Scheme 287

CHART A6 - ENGINE CRANKS BUT WILL NOT RUN (3.0L & 3.8L)

Note. Continued from Chart A5.

1. 6) This test checks for ECM control of the 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 Schematic, Eng. Cranks But Will Not Run (3.0L & 3.8L). Scheme 288

Chart A6 Continued From Chart A-5. Scheme 289

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 26-46 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 and should be (37-43 psi).
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 (33-40 psi). This pressure drop at idle indicates proper regulator control. If fuel is observed in vacuum hose to regulator, the regulator is faulty. Turbo boost pressure will increase fuel line pressure by approximately 1 psi for each pound of manifold boost (46 psi maximum).
3. Pressure that continues to fall is caused by one of the following: the in-tank fuel pump check valve is not holding, pump coupling hose is leaking, pressure regulator valve is leaking or an injector is sticking open.

Chart A7 Fuel Flow Schematic (All Engines). Scheme 290

Note. Fuel System Under Pressure. To Avoid Spillage, Refer To Field Service Procedures For Testing Or Making Repairs Requiring Disassembly Of Fuel Lines Or Fittings.

Chart A7. Scheme 291

CHART A8 - FUEL INJECTION

1. Pressure less than 34 psi can be of 2 types: Regulated pressure less than 34 psi is when the amount of fuel to injector is okay, but pressure is too low. System may be 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 75 psi.
3. This test determines if high pressure is due to a restricted fuel return line or a pressure regulator problem.

Note. Fuel System Under Pressure. To Avoid Fuel Spillage, Refer To Field Service Procedures For Testing Or Making Repairs Requiring Disassembly Of Fuel Lines Or Fittings

Chart A8. Scheme 292

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 the engine is started.

Code 13 Schematic, Open Oxygen Sensor Circuit (All Engines). Scheme 293

Code 13 Chart. Scheme 294

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 term.

"C10". Code 14 will set if signal voltage indicates a coolant temperature more than 270°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), converter clutch (TCC), Canister Purge (CCP), and EGR.

1. This test checks if code was set as a result of a hard failure or intermittent condition.
2. If voltage is more than 4 volts, the ECM and wiring are okay. 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 "C10" and "D2".

Code 14 Schematic, Coolant Sens. Signal Voltage Low (All Engines). Scheme 295

Code 14 Chart. Scheme 296

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.

"C10". 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), Canister Purge (CCP), EGR and converter clutch (TCC).

1. This test checks if code was set as a result of a hard failure or an intermittent condition.
2. If voltage is more than 4 volts, the ECM and wiring are okay. 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 "C10" and "D2".

Code 15 Schematic, Coolant Sensor Signal Voltage High (All Engines). Scheme 297

Code 15 Chart. Scheme 298

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.
2. Code 33 or 34 are not present at start-up.

Possible causes of a Code 21 are faulty TPS, faulty wiring or terminals, or 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 Schematic, TPS Signal Voltage High (All Engines). Scheme 299

Code 21 Chart. Scheme 300

CODE 22 - TPS SIGNAL VOLTAGE LOW

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 22 will set if engine is running and TPS voltage is less than .1 volt for 8 seconds.

Possible causes of a Code 22 are faulty TPS, faulty wiring or terminals, or 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 "C-D" connector before checking circuit for open or short to ground.

Code 22 Schematic, TPS Signal Voltage Low (All Engines). Scheme 301

Code 22 Chart. Scheme 302

CODE 23 - MAT SENSOR SIGNAL VOLTAGE HIGH (3.0L)

The ECM applies 4-6 volts on CKT 472 to the sensor. When the air is cold the sensor resistance is high, therefore the ECM will see a high signal voltage. If the air is warm the sensor resistance will be low, therefore the ECM will see a low signal voltage. Code 23 will be set if the signal voltage indicates manifold air temperature below 40°C for 4 seconds.

1. Code 23 will set due to an open sensor, wire or connection. This test determines if the wiring and ECM are good.
2. If the resistance is greater than 25,000 ohms, replace the sensor.

Code 23 Schematic, MAT Sensor Signal Voltage High (3.0L). Scheme 303

Code 23 Chart. Scheme 304

CODE 24 - VEHICLE SPEED SENSOR ("C" & "N" SERIES)

The ECM supplies a current limited 12 volt signal on circuit 437. The Vehicle Speed Sensor (VSS) senses 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. ECM receives no VSS signal.
2. Engine speed is more than 1800 RPM.
3. Park/Neutral switch indicates transmission is in Drive range.
4. For at least 25 seconds.

1. This test checks for a VSS signal to the ECM while turning drive wheel. Voltage should vary from 4-6 volts.
2. This test checks ECM and wiring harness to VSS buffer.
3. This test checks if ECM recognizes the VSS signal.

Code 24 Schematic, Vehicle Speed Sensor ("C" & "N" Series). Scheme 305

Note. To Prevent Misdiagnosis, Disregard Code 24 If Set When Drive Wheels Are Not Turning.

Code 24 Chart. Scheme 306

CODE 24 - VEHICLE SPEED SENSOR (VSS) "A" BODIES W/ STANDARD CLUSTER

The ECM supplies a current limited 12 volt signal on circuit 437. The Vehicle Speed Sensor (VSS) will sense the speedometer rotating element and furnish this information to the buffer as a "Pulsed" signal, 2 pulses per cable revolution or 20002 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. ECM receives no VSS signal.
2. Engine speed is more than 1800 RPM.
3. Park/Neutral switch indicates transmission is in Drive range.
4. For at least 25 seconds.

1. This test checks if there is a VSS signal to the ECM while turning drive wheel. Voltage should vary from less than 2 volts to more than 8 volts with less variation as wheel speed increases.
2. This test checks ECM and wiring harness to I.P. cluster.
3. This test checks if ECM recognizes the VSS signal.

Code 24 Schematic, VSS - "A" Bodies With Standard Cluster. Scheme 307

Note. To Prevent Misdiagnosis, Disregard Code 24 If Set When Drive Wheels Are Not Turning.

Code 24 Chart. Scheme 308

CODE 24, VEHICLE SPEED SENSOR (VSS) "A" BODIES W/ DIGITAL INSTRUMENT CLUSTER

The ECM supplies a current limited 12 volt signal on circuit 437. The Vehicle Speed Sensor (VSS) 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. ECM receives no VSS signal.
2. Engine speed is more than 1800 RPM.
3. Park/Neutral switch indicates transmission is in Drive range.
4. For at least 25 seconds.

1. This test checks for a VSS signal to the ECM while turning drive wheel. Voltage should vary from 4-6 volts.
2. This test checks ECM and wiring harness to VSS buffer.
3. This test checks if ECM recognizes the VSS signal.

Code 24 Chart. Scheme 309

CODE 24 - VEHICLE SPEED SENSOR ("E" & "G" SERIES)

The ECM supplies a current limited 12 volt signal on circuit 437. The Vehicle Speed Sensor (VSS) will sense speedometer rotating elements 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. ECM receives no VSS signal.
2. Engine speed is more than 1400 RPM.
3. Park/Neutral switch indicates transmission is in Drive range.
4. For at least 20 seconds.

1. This test checks if there is a VSS signal to the ECM while turning drive wheel. Voltage should vary from 4-6 volts.
2. This test checks ECM and wiring harness to VSS buffer.
3. This test checks if ECM recognizes the VSS signal.

Note. To Prevent Misdiagnosis, Disregard Code 24 If Set When Drive Wheels Are Not Turning.

Code 24 Chart. Scheme 310

CODE 31 - WASTEGATE SOLENOID (3.8L TURBO)

The wastegate solenoid allows the ECM to increase turbo boost beyond the precalibrated level that is normally controlled by the wastegate actuator assembly. Code 31 sets when the ECM is commanding a duty cycle between 5-95% and no voltage pulses are received on the wastegate monitor. This condition must last more than 5 seconds.

1. This test checks to see if circuit 928 is shorted to ground.
2. This test checks for an open circuit 928 to ECM. Grounding THE TEST terminal should turn the test light "ON".
3. This test locates an open or short to voltage that is the source of the problem.

Code 31 Schematic, Wastegate Solenoid (3.8L Turbo). Scheme 311

Code 31 Chart. Scheme 312

CODE 32 - EGR VACUUM CONTROL (3.0L & 3.8L)

The EGR vacuum control circuit has an ECM controlled solenoid that pulses manifold vacuum to the EGR valve. The solenoid is always de-energized (EGR "OFF") in Park or Neutral and at idle. The circuit also includes vacuum diagnostic switch which is open with no vacuum applied to the EGR. The diagnostic switch signals the ECM when vacuum is being applied to the EGR valve. Code 32 will set if the EGR diagnostic vacuum switch senses vacuum at idle, or if it does not sense vacuum in gear with moderate to heavy engine load, but less than wide open throttle.

1. This test checks for presence of vacuum to EGR valve at idle (closed vacuum switch).
2. Grounding the test terminal causes the ECM to energize the solenoid by grounding circuit 435. Test light should be "ON".
3. Light "ON" indicates vacuum at EGR. Vacuum should not be present.
4. Normal response is "CHECK ENGINE" light "OFF". This indicates vacuum switch is open.
5. "CHECK ENGINE" light "ON" indicates circuit 932 shorted to ground, or contacts stuck closed in EGR vacuum diagnostic switch.

Code 32 Schematic, EGR Vacuum Control (3.0L & 3.8L). Scheme 313

Code 32 (3.0L & 3.8L)(1 Of 2). Scheme 314

Code 32 (3.0L & 3.8L) (2 Of 2). Scheme 315

CODE 32, EXHAUST GAS RECIRCULATION (EGR) VACUUM CONTROL (3.8L TURBO)

The EGR vacuum control circuit has an ECM controlled solenoid that pulses manifold vacuum to the EGR valve. The solenoid is always de-energized (EGR "OFF") in Park or Neutral and at idle. The circuit also includes vacuum diagnostic switch which is open with no vacuum applied to the EGR. The diagnostic switch signals the ECM when vacuum is being applied to the EGR valve. Code 32 will set if the EGR diagnostic vacuum switch senses vacuum at idle, or if it does not sense vacuum in gear with moderate to heavy engine load, but less than wide open throttle.

1. This test checks for presence of vacuum to EGR valve at idle (closed vacuum switch).
2. Grounding the test terminal causes the ECM to energize the solenoid by grounding circuit 435. Test light should be "ON."
3. Light "ON" indicates vacuum at EGR. Vacuum should not be present.
4. Normal response is "CHECK ENGINE" light "OFF". This indicates vacuum switch is open.
5. "CHECK ENGINE" light "ON" indicates circuit 932 shorted to ground, or contacts stuck closed in EGR vacuum diagnostic switch.

Code 32 (3.8L Turbo) (1 Of 2). Scheme 316

Code 32 (3.8L Turbo) (2 Of 2). Scheme 317

CODE 33 - MASS AIR FLOW (MAF) SENSOR

The MAF sensor measures the flow of air entering the engine. This information is used by the ECM for fuel control. To set Code 33 the following conditions must be met for 5 seconds or more: * Engine idling.

1. TPS is 10% or less.
2. Air flow is more than 150 grams per second (high frequency).

1. This test checks if ECM recognizes a problem.
2. Inspect wire routing of high voltage wires such as spark plug wires. Such wires routed too closely to MAF wiring harness could possibly cause an intermittent Code 33.

Code 33 Schematic, Mass Air Flow (MAF) Sensor (All Engines). Scheme 318

Code 33 Chart. Scheme 319

CODE 34 - MASS AIR FLOW (MAF) SENSOR

The MAF sensor measures the flow of air entering the engine. This information is used by the ECM for fuel control. Code 34 is set when the engine is running with MAF sensor disconnected or the engine is running faster than 1400 RPM with the TPS signal more than 50% (2.5 volts) and the air flow less than 10 grams per second (low frequency).

1. A loose or damaged air duct can set Code 34.
2. This test checks if ECM recognizes a problem. "CHECK ENGINE" light "OFF" indicates an intermittent problem.
3. This test checks if 5 volt reference signal from ECM is at MAF sensor harness connector. Less than 1 volt here indicates a faulty circuit 492, wiring connector or ECM.
4. This test checks continuity of electrical circuit.
5. This test checks for open in ignition circuit.

Code 34 Schematic, Mass Air Flow (MAF) Sensor (All Engines). Scheme 320

Code 34 Chart. Scheme 321

CODE 41 - C(3)I IGNITION CAM SENSOR SIGNAL (3.8L TURBO)

The cam sensor is a magnetic "hall switch" that provides the ECM with a voltage signal on the No. 1 cylinder compression stroke. This information is used by the ECM to properly time sequential fuel injection. When the cam signal is not received by the ECM, the injection is simultaneous rather than sequential. Code 41 will set when the engine is running and the cam sensor signal is not seen by the ECM for 1 second.

1. This test checks if the ECM recognizes a problem and sets a failure code.
2. The voltage recorded is 12 volts supplied by the ignition module. Voltage must be pulsed by the cam sensor to be recognized by the ECM as a signal of 2 to 9 volts. This is why the voltage is checked while cranking the engine.

Code 41 Schematic, C(3)I Ignition Cam Sensor Signal (3.8L Turbo). Scheme 322

Code 41 Chart. Scheme 323

CODE 42 - C(3)I IGNITION (3.0L)

Code 42 indicates that the ECM has seen an open or grounded bypass or EST circuit with engine running.

1. & 5) This test checks to see if ECM recognizes a problem. If it doesn't set Code 42, problem is intermittent and could be due to a loose connection.
2. With the ECM disconnected, the ohmmeter should indicate normal resistance of the ignition module (less than 200 ohms).
3. This test checks if ignition module switches when the bypass circuit is energized by 12 volts through the test light. If the ignition module switches, the ohmmeter will read more than 8000 ohms.
4. Disconnecting the ignition module should make the ohmmeter read as if it were seeing an open circuit. If the ohmmeter displays a low reading, circuit 423 is shorted to ground.

Code 42 Schematic, C(3)I Ignition (3.0L). Scheme 324

Code 42 Chart. Scheme 325

CODE 42 - ELECTRONIC SPARK TIMING (EST) (3.8L)

Code 42 indicates that the ECM has seen an open or grounded bypass, or EST circuit, with engine running.

1. Grounding the diagnostic terminal should cause the ECM to set a fixed timing value. Timing should change compared to the timing before grounding terminal. This indicates the EST system is working.
2. Jumpering "B" to "B" and "D" to "D" completes the reference circuit so the car will run. Measuring "A" voltage checks the EST signal from the ECM.
3. Jumpering "A" to "A" completes the EST circuit with the bypass circuit still open. Now the engine is running on module timing. In this condition, the EST circuit is grounded by the HEI module so the EST voltage should now be less than .4 volt.
4. The test light serves as a jumper to apply voltage to the bypass terminal. This will switch the module to allow EST. Because the EST signal will no longer be grounded, there should be a voltage reading on the EST circuit.
5. This test checks the bypass circuit in the ECM. Normal reading is 4-5 volts with engine running.

Code 42 Schematic, Electronic Spark Timing (EST) (3.8L). Scheme 326

Code 42 Chart. Scheme 327

CODE 43 - ELECTRONIC SPARK CONTROL

Code 43 indicates that the ECM has seen low voltage at CKT 457 for longer than 4 seconds with the engine running. This voltage drops when ESC module shuts off because it receives a knock signal.

1. This test checks if ECM recognizes a problem.
2. The ESC module supplies voltage to the ECM. It should always be over 6 volts unless the system is sensing engine detonation.
3. 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.
4. This test checks for grounded ECM.
5. This test checks open ignition circuit.

Code 43 Schematic, Electronic Spark Control (All Engines). Scheme 328

Code 43 Chart. Scheme 329

CODE 44 - LEAN EXHAUST INDICATION

Code 44 indicates that the ECM has seen O2 sensor voltage (at ECM term. "D7") lower than .2 volts for 1 minute or more, 2 minutes after engine start. The ECM supplies a voltage of about .45 volt between terms. "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 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, fuel contaminated, O2 sensor wire grounded, EGR not opening, or MAP sensor giving false low pressure reading. If these 6 systems are found to be operating, O2 sensor is faulty.

Code 44 Schematic, Lean Exhaust Indication (All Engines). Scheme 330

Code 44 Chart. Scheme 331

CODE 45 - RICH EXHAUST INDICATION

Code 45 indicates that the ECM has seen O2 sensor voltage (at ECM term. "D7") lower than .7 volts for 30 seconds or more, 1 minute after engine start. The ECM supplies a voltage of about .45 volt between terms. "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 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.

Code 45 WILL NOT be set by a faulty O2 sensor. Code 45 indicates a rich exhaust and diagnosis should begin with these items

1. A silicon contaminated O2 sensor will cause a steady signal above .55 volts and set code 45.
2. Fuel Pressure. System will go rich if pressure is too high. The ECM can compensate for some increase. However, if it gets too high.
3. A Code 45 may be set by a leaking fuel pressure regulator leaking injector. See Chart A7
4. HEI Shielding. An open ground circuit 453 may result in EMI, or induced electrical "noise". The ECM looks at this "noise" as distributor pulses. The additional pulses result in a higher than actual engine speed signal. The ECM then delivers too much fuel, causing system to go rich. Engine tachometer will also show higher than actual engine speed, which can help in diagnosing this problem.
5. Canister purge. Check for fuel saturation. If full of fuel, see Chart C3.
6. MAF sensor. An output that causes the ECM to sense a higher than normal manifold air flow can cause the system to go rich. Disconnecting MAF sensor will allow the ECM to set a fixed value for the MAF sensor. Substitute a different MAF sensor if the rich condition is gone while the sensor is disconnected.
7. TPS. An intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.

Code 45 Schematic, Rich Exhaust Indication (All Engines). Scheme 332

Code 45 Chart. Scheme 333

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 51 Chart. Scheme 334

Code 52 Chart. Scheme 335

CODE 55 - REPLACE ECM

Clear Codes and confirm "CLOSED LOOP" operation and no "CHECK ENGINE" light.

Code 55 Chart. Scheme 336

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)

Note. Use this chart only after the normal diagnostic charts have determined that there is an ECM failure.

Chart C-1. Scheme 337

Chart C1A. Scheme 338

Chart C1A. Scheme 339

Chart C1E. Scheme 340

Chart C2C. Scheme 341

CHART C3 - CANISTER PURGE VALVE

Canister purge is controlled by a solenoid that allows manifold vacuum to purge the canister when energized. The ECM supplies a ground to energize the solenoid (purge on).

If the diagnostic test terminal is grounded with the engine stopped or the following is met with the engine running the purge solenoid is de-energized (purge on).

1. Engine run time after start more than 1 minute.
2. Coolant temperature above 80°C (176°F).
3. Vehicle speed above 5 MPH (8 km/h).
4. Throttle off idle. TPS signal about .75 volt.

1. Checks to see if the solenoid is opened or closed. The solenoid is normally de-energized in this step, so it should be closed.
2. Completes functional check by grounding test terminal. This should be normally energize the solenoid and allow the vacuum to drop (purge on).
3. Check for open or grounded solenoid circuit.
4. Checks to see if ECM control circuit or solenoid is at fault.

Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM. Using an ohmmeter, check the purge solenoid, coolant fan relay, or wastegate solenoid (E and G Series only) resistance before installing a replacement ECM, because they could cause failure of the purge circuit.

Chart C3 Schematic - Canister Purge Valve. Scheme 342

Chart C3. Scheme 343

Chart C4 (1 Of 2). Scheme 344

Chart C4 (2 Of 2). Scheme 345

CHART C-4A - IGNITION SYSTEM CHECK (3.0L)

For timing spark plug firing, a dual crankshaft sensor is used. Cam signal part of this switch sends a signal to ignition module when No. 1 cylinder is on compression stroke. The signal is used by ignition module to start correct ignition coil firing sequence. engine will still operate if cam signal is lost while running. However, it will not restart after shut-down and Code 41 will be set in memory.

Crankshaft signal part of switch also sends a signal to ignition module. This signal is then passed on to the Electronic Control Module (ECM) for RPM reference and crankshaft position information.

Chart C-4A, C3I Ignition System Check Schematic (3.0L). Scheme 346

Chart C-4A. Scheme 347

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

1. If plug wire is open, other plug on that coil may still fire at idle. This tests ability of system to produce at least 25,000 volts.
2. No spark on one cylinder may be caused by an open plug wire or open secondary winding. Both plug wires related to each coil and the secondary winding resistance should be checked. Resistance readings over upper limit, but not infinite, will probably not cause a no start, but may cause an engine misfire under certain conditions.
3. Tests triggering circuit in the ignition module. A blinking light indicates module is triggering. The mini-schematic shows control wire for each coil. For example, if testing why No. 1 plug did not fire, connect test light between the Blue feed wire and Yellow/Black control wire.
4. ECM terminal "B-5" is the reference signal to ECM as generated by the crankshaft sensor. The signal goes from high to low during crank and will read 1-7 volts. A steady voltage reading, either high or low, indicates a faulty signal. This test checks cam and crankshaft sensor, because if cam sensor is inoperative, ignition module will not allow reference signal to reach ECM on circuit No. 430.
5. A separate 10-amp, 12 volt feed is used for the primary windings of the coils. This check will determine if 12 volts are reaching the coils.
6. If 12 volts are reaching ignition module on terminal "M" and connection is good but 12 volts were not detected at the common feed Blue wire at coils, module is open internally and must be replaced. If 12 volts are not reaching the module on terminal "M", ignition feed wire and 25-amp fuse must be checked.

Chart C-4A (2 of 2) Continued From Chart C-4A (1 Of 2). Scheme 348

Chart C-4A (2 of 2) Continued From Chart C-4A (1 Of 2)(continued). Scheme 349

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

1. 1) This check will determine if the cam sensor signal is reaching the module. A steady high or low voltage on terminal "A11" indicates a faulty signal.
2. 2) Probing terminals "A" and "B" of sensor connector on the module side checks the voltage supply through the module and the connections at the module.
3. 2a) Checks for an open sensor ground circuit.
4. 3) Checks for the 12-volt power supply reaching the module on terminal "P". If the 12 volts are present at "P" but were not present at the sensor connector terminal "A" and all connections are good, the ignition module must be open internally.
5. 4) In this step the "B" or "C" terminal is removed and a jumper wire is installed to allow for access to the signal wire being tested.
6. 5) If the sensor is functioning properly and the wiring and connections are good, the ignition module is at fault.
7. 6) Probing terminals "A" and "C" of the sensor connector on the module side checks the sensor supply voltage through the module and the connections at the module.
8. 6a) Checks for an open sensor ground circuit.
9. 7) Checks voltage at terminal "F" and "H". If okay, the ignition module is bad.
10. 8) If the sensor is functioning properly and the wiring connection is good, the ignition module is faulty.

Test Description For Steps 1-5 (3.0L VIN L)

The C(3)I ignition system uses a waste spark method of spark distribution. In this type of ignition system, the ignition module triggers the 1/4 coil pair, resulting in the Nos. 1 and 4 spark plug firing at the same time. The No. 1 cylinder is on the compression stroke while the No. 4 cylinder is on it's exhaust stroke, resulting in a lower energy requirement to fire the No. 4 spark plug. This leaves the remaining high voltage to fire the No. 1 spark plug.

Note. Test numbers below refer to the circled numbers on the diagnostic chart.

1. If the misfire complaint exists UNDER LOAD only, refer to CHART C4F-2 - MISFIRES UNDER LOAD (3.0L VIN L). Engine RPM should drop approximately the same for each cylinder.
2. A spark tester such as an ST-125 must be used because it is essential to verify adequate available secondary voltage at the spark plug. Secondary voltage of at least 25,000 volts must be present to jump the gap of the ST-125.
3. If the ignition coils are carbon tracked, the coil tower spark plug wire nipples may be damaged.
4. By checking the secondary resistance, a coil with an open secondary may be located.
5. By switching a normally operating coil into the position of the malfunctioning one, a determination can be made as to whether the fault is the coil or the C3I module.

Note. In the following circuit schematic, circuit numbers and wire colors may vary between vehicles. However, pin numbers and components represented are accurate.

Chart C4F-1. Scheme 350

Test Description For Steps 1-5 (3.8L VINS 3 & B)

The C(3)I ignition system uses a waste spark method of spark distribution. In this type of ignition system, the ignition module triggers the 1/4 coil pair, resulting in the Nos. 1 and 4 spark plug firing at the same time. The No. 1 cylinder is on the compression stroke while the No. 4 cylinder is on it's exhaust stroke, resulting in a lower energy requirement to fire the No. 4 spark plug. This leaves the remaining high voltage to fire the No. 1 spark plug.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. see scheme 98

1. If the misfire complaint exists UNDER LOAD only, refer to CHART C4F-2 - MISFIRES UNDER LOAD (3.8L VINS 3 & B). Engine RPM should drop approximately the same for each cylinder.
2. A spark tester such as an ST-125 must be used because it is essential to verify adequate available secondary voltage at the spark plug. Secondary voltage of at least 25,000 volts must be present to jump the gap of the ST-125.
3. If the ignition coils are carbon tracked, the coil tower spark plug wire nipples may be damaged.
4. By checking the secondary resistance, a coil with an open secondary may be located.
5. By switching a normally operating coil into the position of the malfunctioning one, a determination can be made as to whether the fault is the coil or the C3I module.

Note. In the following circuit schematic, circuit numbers and wire colors may vary between vehicles. However, pin numbers and components represented are accurate.

Chart C4F-1. Scheme 351

Test Description For Steps 1-4 (3.0L VIN L & 3.8L VINS 3 & B)

The C(3)I ignition system uses a waste spark method of spark distribution. In this type of ignition system, the ignition module triggers the 1/4 coil pair, resulting in the Nos. 1 and 4 spark plug firing at the same time. The No. 1 cylinder is on the compression stroke while the No. 4 cylinder is on it's exhaust stroke, resulting in a lower energy requirement to fire the No. 4 spark plug. This leaves the remaining high voltage to fire the No. 1 spark plug.

Note. Test numbers below refer to the circled numbers on the diagnostic chart. see scheme 102-46.

1. If the misfire complaint exists AT IDLE only, refer to CHART C4F-1 - MISFIRES AT IDLE (3.0L VIN L). Engine RPM should drop approximately the same for each cylinder.
2. A spark tester such as an ST-125 must be used because it is essential to verify adequate available secondary voltage at the spark plug. Secondary voltage of at least 25,000 volts must be present to jump the gap of the ST-125. Spark should jump the tester gap on all 6 leads. This simulates a "Load" condition.
3. If the ignition coils are carbon tracked, the coil tower spark plug wire nipples may be damaged.
4. By switching a normally operating coil into the position of the malfunctioning one, a determination can be made as to whether the fault is the coil or the C3I module.

Note. In the following circuit schematic, circuit numbers and wire colors may vary between vehicles. However, pin numbers and components represented are accurate.

Chart C4F-2. Scheme 352

CHART C5 - ELECTRONIC SPARK CONTROL (ESC) SYSTEM CHECK

This Chart Should Only Be Used After All Other Causes Of

Spark Knock Have Been Checked I.E., Timing, EGR, Engine

Temperature Or Excessive Engine Noise, Etc.

Chart C5. Scheme 353

Chart C7. Scheme 354

Chart C8 (1 Of 2). Scheme 355

Chart C8 (2 Of 2). Scheme 356

Chart C8A. Scheme 357

Chart C8B. Scheme 358

Chart C10A. Scheme 359

Chart C10B Continued From Chart C-10A. Scheme 360

Chart C10A. Scheme 361

Chart C10B Continued From Chart C-10A. Scheme 362

Chart C12A. Scheme 363

Chart C12B. Scheme 364

Chart C12C. Scheme 365

*

With heavy duty cooling (VO8), two fan motors are used. During hi speed operation, both fans should be "ON". If only one motor operates, treat this as fan "OFF".

Chart-C12D. Scheme 366

Component Location for 3.0L & 3.8L Engines. Scheme 367

Port Fuel Injection ECM Terminal Identification 3.0L. Scheme 368

Port Fuel Injection ECM Terminal Identification 3.8L. Scheme 369

Port Fuel Injection ECM Terminal ID 3.8L Turbo. Scheme 370

Port Fuel Injection Wiring Diagram 3.0L. Scheme 371

Port Fuel Injection Wiring Diagram 3.8L (Exc. Turbo). Scheme 372

Port Fuel Injection Wiring Diagram 3.8L Turbo. Scheme 373