Tests W/codes - 3.0l VIN (l) & 3.8l VIN (3 & 7) Buick Electra VI

MODEL IDENTIFICATION

Note. The following conditions must be met before testing: Engine at operating temperature, Engine in closed loop operation, Engine idling ("Engine Run" column), Test terminal NOT grounded, and Scanner or ALDL tool NOT installed.

Repair procedures in this article are sometimes identified by a specific body code. The following table lists GM division, model name, and body types that apply to the body codes.

MODEL IDENTIFICATION

DESCRIPTION & OPERATION

The computerized engine control system monitors as many as 19 engine/vehicle functions. (Scheme 49) This system controls engine operation and lowers exhaust emissions while maintaining fuel economy and driveability. The Electronic Control Module (ECM) is the "brain" of the CCC system.

The computerized engine control 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 3-way catalytic converter can control Oxides of Nitrogen (NOx), Hydrocarbon (HC) and Carbon Monoxide (CO) emissions.

ECM Conditions Sensed & Systems Controlled. Scheme 49

DIAGNOSTIC SYSTEM OPERATION

The ECM of computerized engine control system is equipped with a self-diagnostic system which detects system failures or abnormalities. As a bulb and system check, "SERVICE ENGINE SOON" light will glow when ignition switch is turned to "ON" position and engine is not running. When engine is started, light should go out. If not, a malfunction has been detected in the computerized engine control system or "SERVICE ENGINE SOON" light circuit is faulty.

When a malfunction occurs, ECM will illuminate the "SERVICE ENGINE SOON" light located on instrument panel. When malfunction is detected and light is turned on, a corresponding trouble code will be stored in ECM memory. Malfunctions are recorded as "hard failures" or as "intermittent failures".

"HARD FAILURES"

Hard failures cause "SERVICE ENGINE SOON" light to glow and remain on until the malfunction is repaired. If light comes on and remains on during vehicle operation, cause of malfunction must be determined using diagnostic charts. If a sensor fails, ECM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is driveable, but loss of good driveability will most likely be encountered.

"INTERMITTENT FAILURES"

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

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds. Others may require operation for 5 minutes or longer under engine load.

BASIC DIAGNOSTIC PROCEDURE

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

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

1. Make sure that all engine systems not related to the computer system are operating properly. Do not proceed with testing unless all other problems have been repaired.
2. Perform appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If trouble codes were displayed (other than Code 12), decide whether codes are "hard" or "intermittent" trouble codes. "Hard" codes will cause the "SERVICE ENGINE SOON" light to illuminate continuously while engine is running. See ECM TROUBLE CODE DEFINITIONS table in this article.
3. If no trouble codes were displayed, perform FIELD SERVICE MODE CHECK procedures.
4. If no trouble is indicated by the FIELD SERVICE MODE check and/or a driveability problem exists, refer to SYMPTOM DIAGNOSIS and/or SCAN TESTER USAGE in this article. The comments there will send you to the proper component charts or tell you the most likely system/component to check.
5. After any repairs are made, clear any trouble codes and perform FIELD SERVICE MODE check again.

Scheme 50

1. Turn ignition on. Do not start engine. "SERVICE ENGINE SOON" light should glow. Locate Assembly Line Data Link (ALDL) connector attached to ECM wiring harness under instrument panel, left or right of steering column (under cigar lighter plate in center console on Fiero). Insert jumper wire across terminal "B", "DIAGNOSTIC TERMINAL" and terminal "A", "GROUND". (Scheme 50) CAUTION: Inserting spade lug (jumper lead) into terminals of ALDL connector grounds "DIAGNOSTIC TERMINAL". Do not ground ALDL connector until after ignition is on (engine not running). (Scheme 50): ALDL Connector Terminal Identification NOTE: In some of the diagnostic and trouble shooting charts the Assembly Line Data Link (ALDL) may also be referred to as the Assembly Line Communication Link (ALCL). These are referring to the same connector. It is also the test point for connection of aftermarket "Scan" testers.
2. "SERVICE ENGINE SOON" 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. If any other trouble codes are stored in ECM memory, they will be displayed in the same manner.
3. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.

READING TROUBLE CODES

The ECM stores component failure information for the CCC system under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of the "SERVICE ENGINE SOON" light, or by reading the output of a diagnostic "Scan" tester connected to the ALDL connector. The tester is faster, more accurate, and capable of reading information which otherwise would necessitate testing individual ECM and sensor/solenoid connector terminals with a volt/ohmmeter. See SCAN TESTER - TEST DATA PARAMETERS table and SCAN TESTER USAGE in this article.

If "Scan" tester is not available, it is possible to read flashes of the dashboard "SERVICE ENGINE SOON" light by grounding the diagnostic terminal of the ALDL with ignition on and engine off. 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. Trouble codes are displayed starting with the lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL "DIAGNOSTIC TERMINAL" is grounded.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others may require operation for 5 minutes or longer at normal operating temperature, road speed and load. Therefore, some codes may not set in a service bay operational mode.

ECM TROUBLE CODE DEFINITIONS

ECM TROUBLE CODE DEFINITION

Note. Trouble code charts should only be used if "SERVICE ENGINE SOON" light is illuminated (indicating a current problem exists). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes.

Note. Any time Codes 51, 52, 54 or 55 are displayed with another code, start with "50-series" code first, then proceed to low profile numbered code.

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" codes. To determine "hard" codes and "intermittent" codes, proceed as follows

1. Manually enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode and clear trouble codes.
2. Apply parking brake and place transmission in Neutral (man. trans.) or "P" (auto. trans.). Block drive wheels. Start engine. "SERVICE ENGINE SOON" light should go out. Run warm engine at specified curb idle for 2 minutes. Note "SERVICE ENGINE SOON" light.
3. If "SERVICE ENGINE SOON" 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.
4. If "SERVICE ENGINE SOON" light does not come on, all stored trouble codes were "intermittent failures". Exceptions are noted under DIAGNOSTIC PROCEDURE.

CLEARING TROUBLE CODES

Turn ignition switch to "ON" position and ground "DIAGNOSTIC TERMINAL" lead at ALDL connector. Turn ignition switch to "OFF" position and remove ECM fuse from fuse block for 10 seconds. Replace fuse. Remove "DIAGNOSTIC TERMINAL" ground lead.

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 test the reliability of the self-diagnostic system.
2. Charts which help fix problems which are "SERVICE ENGINE SOON" light related.
3. Charts which test the computerized fuel control system performance.
4. Charts which help fix a problem when the on-car diagnostics don't work.
5. ENGINE CRANKS BUT WON'T RUN charts. Refer to the appropriate TROUBLE SHOOTING chart in the CCC TESTS W/O CODES article in this section.
6. Charts where a stored trouble code leads you to a particular problem. See ECM TROUBLE CODE DEFINITION and DIAGNOSTIC AIDS in this article. Charts which are used because the FIELD SERVICE MODE CHECK found a problem.

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

Diagnostic Aids

Diagnostic aids (located in each "trouble code" chart box for each system) are additional tips used to help diagnose trouble codes when inspected circuit checks out okay. Diagnostic aids may help lead to a definitive solution to that trouble code problem.

FIELD SERVICE MODE CHECK (FUEL INJECTED MODELS)

On fuel injected models, "SERVICE ENGINE SOON" light will indicate operational mode of engine if ALDL is grounded while engine is running. In closed loop mode, "SERVICE ENGINE SOON" light will flash at a rate of one flash per second. In open loop, light will flash at a rate of 2.5 flashes per second. If light is off all or most of the time, a lean exhaust is indicated. If light is on all or most of the time, a rich exhaust is indicated.

This test confirms proper operation of fuel system and verifies closed loop operation. Clear codes and perform this test after any repair is completed. When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on front-wheel drive models does NOT hold drive wheels.

Note. On some engines, 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.

SPECIAL DIAGNOSTIC TOOLS

Note. Special "Scan" testers plugged into the ALDL may be used to read trouble codes and check voltages in the system on the serial data line (terminal "E" on EFI and terminal "M" on EFI with P-4 systems). These testers can save a great deal of time. For additional information see SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS table in this article.

The computerized engine control system is most easily diagnosed using a "Scan" tester, however, other tools may aid in diagnosing problems if a "Scan" tester is unavailable. These tools are: a tachometer, a dwell meter, test light, ohmmeter, digital voltmeter with 10-megohm impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights (TBI and PFI) and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connector at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

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

When engine is at operating temperature and idling, dwell meter needle should vary between 10-50 degrees. This indicates closed loop operation. Before engine reaches operating temperature, dwell should be fixed between 10-50 degrees, indicating open loop operation. If after reaching normal operating temperature dwell is fixed between 10-50 degrees, less than 10 degrees or more than 50 degrees, refer to appropriate CHART A - DWELL FIXED diagnostic chart for that system.

SCAN TESTER USAGE

Note. Prior to connection of scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received by scan tester will be accurate. This is done by performing appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If vehicle does not pass diagnostic circuit check, information received by scan tester may be invalid. CCC Scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on- board computer control stems by providing instant access to circuit voltage information without need to crawl under dash or hood to back-probe sensors and connectors.

Scan testers cut down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN TESTER - TEST DATA PARAMETERS table. They also furnish information on output device (solenoids and motors) status. Status parameters, however, are only an indication that output signals have been sent to devices by the ECM. It does not indicate if devices have responded properly to that signal. This will need to be verified at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine not running but may not be indicated by all makes of scan tester.

If trouble codes are not present, this is not an indication that there is not a problem. CCC related problems are about 20 percent codes and 80 percent driveability. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Use of a scan tester is easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See the SCAN TESTER - TEST DATA PARAMETERS table below.

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, it will be necessary to verify tester information using a digital voltmeter and wiring schematic. If non- existent codes are in evidence, turn ignition off, remove tester, turn ignition on and ground ALDL "DIAGNOSTIC TERMINAL". If same codes are not flashed by "SERVICE ENGINE SOON" light that were indicated by scan tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate.

SCAN TESTER - TEST DATA PARAMETERS

Note. Information in the following tables is typical readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are virtually instantaneous. Not all devices & systems are used on all models.

PORT FUEL INJECTION

DIAGNOSTIC CONNECTOR LOCATION

DIAGNOSTIC CONNECTOR LOCATION

DIAGNOSTIC CIRCUIT CHECK

The diagnostic circuit check is an organized approach for identifying a problem caused by an electronic control system malfunction. If after completing the diagnostic circuit check, no problems were found, a comparison of "Scan" tester parameters may be used to help locate intermittents and out-of-specification sensors. See the SCAN TESTER - TEST DATA PARAMETERS table above this paragraph.

If the "Scan" tester is not operating properly, check on another vehicle. If okay, the cigar lighter socket should be checked for 12 volts and a good ground. If the "Scan" tester reads "NO DATA" or "NO ALDL", with the ignition on, check the serial data wire for an open or short to ground between ALDL terminal "E" and the ECM. Also check for an open diagnostic test terminal from ALDL terminal "B" and ECM. With ignition on, the serial data line should have a between 2-5 volts and the diagnostic line about 5 volts.

Diagnostic Circuit Check. Scheme 51

"SCAN" DIAGNOSTIC CIRCUIT CHECK

The "SCAN" Diagnostic Circuit Check is an organized approach for identifying fuel injection problems using an assembly line communication link (ALCL). This communication link can provide diagnostic information for display on any "SCAN" device or tool designed for this purpose.

1. If the "SCAN" tester is not operating, check on another vehicle. If okay, the cigar lighter socket should be checked for 12 volts and a good ground. If the "SCAN" tester reads "no data" or "no ALCL", with the ignition on, check the serial data wire for an open or short to ground between ALCL terminal "E" and the ECM. Also check for an open diagnostic test terminal from ALCL terminal "B" and ECM. With ignition on, the serial data line should have a between 2-5 volts and the diagnostic line about 5 volts.
2. See the CCC TESTS W/O CODES article in this section.
3. See the CCC TESTS W/O CODES article in this section.

"Scan" Diagnostic Circuit Check - Schematic. Scheme 52

"Scan" Diagnostic Circuit Check. Scheme 53

DIAGNOSTIC TROUBLE CODE IDENTIFICATION

DIAGNOSTIC TROUBLE CODE IDENTIFICATION

CHART A1 - NO "SERVICE ENGINE SOON" LIGHT

"SERVICE ENGINE SOON" 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 No. 419.

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

1. The "SERVICE ENGINE SOON" light should be on as the test light provides a ground.
2. Using a test light connected to 12 volts, probe each of the system ground circuits to be sure a good ground is present.

Engine Runs Okay

1. Check for faulty light bulb.
2. Check for open in circuit No. 419.

Engine Cranks, But Will Not Run

1. Check continuous battery power, check fuse or fusible link for open.
2. Check for ECM ignition fuse open.
3. Check for ignition circuit No. 439 to ECM open.
4. Check for poor connection to ECM.

Chart A1, Schematic. Scheme 54

Chart A1, No "Service Engine Soon" Light. Scheme 55

Won't Flash Code 12 "Service Engine Soon" ("SES") Light On

"SERVICE ENGINE SOON" light should be on steady when ignition is on and engine is off. Battery voltage is supplied to the light bulb and light bulb is grounded by ECM through circuit No. 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 No. 419, or an open in diagnostic circuit No. 451.

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

1. If there is a problem with the ECM that causes a "Scan" tester to not read serial data, the ECM should not flash a Code 12. If Code 12 does flash, be sure that the "Scan" tester is working properly on another vehicle. If the "Scan" tester is functioning properly and circuit No. 451 is okay, the PROM or ECM may be at fault for the "NO ALDL" symptom.
2. If the light goes off when the ECM connector is disconnected, then circuit No. 419 is not shorted to ground.
3. This test will check for an open diagnostic circuit 451.
4. At this point, the "SERVICE ENGINE SOON" light wiring is okay. The problem is a faulty ECM or PROM. If Code 12 does not flash, the ECM should be replaced using the original PROM. Replace the PROM only after trying a new ECM, as a defective PROM is an unlikely cause of the problem.

Won't Flash Code 12 "Service Engine Soon" Light On. Scheme 56

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

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 For Steps 1-6 (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 its 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.

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.

Ignition System Schematic (3.0L, VIN L). Scheme 57

Chart A3 (1 of 3), Cranks But Won't Run (3.0L, VIN L). Scheme 58

Circuit Description For Steps 7-11 (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.

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.

Chart A3 (2 of 3), Cranks But Won't Run (3.0L, VIN L). Scheme 59

Circuit Description For Steps 12 & 13 (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.

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.

Chart A3 (3 of 3), Cranks But Won't Run (3.0L, VIN L). Scheme 60

Engine Cranks But Won't Run (3.8L Non-Turbo With Type I Ignition 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 (1 Of 3, 3.8L Non-Turbo With Type I Ignition System)

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 its 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.

Ignition System Schematic (3.8L, W/ Type I Ignition System). Scheme 61

Flowchart A3 (1 of 3), Cranks/Won't Run (3.8L W/ Type I Ignition System). Scheme 62

Circuit Description For Steps 7-11 (2 Of 3, 3.8L Non-Turbo With Type I Ignition System)

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.

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/Won't Run (3.8L W/ Type I Ignition System). Scheme 63

Flow Chart A3 (2 of 3, Part 1), Cranks/Won't Run (3.8L W/ Type I Ignition System). Scheme 64

Flow Chart A3 (2 of 3, Part 2), Cranks/Won't Run (3.8L W/ Type I Ignition System). Scheme 65

Circuit Description For Steps 12-14 (3 Of 3, 3.8L Non-Turbo With Type I Ignition System)

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.

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/Won't Run (3.8L W/ Type I Ignition System). Scheme 66

Flow Chart A3 (3 of 3). Scheme 67

Engine Cranks But Won't Run (1 Of 3, 3.8L Non-Turbo W/ Type II Ignition 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 (1 Of 3, Type II Ignition)

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 its 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 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.

Ignition System Schematic (3.8L W/ Type II Ignition System). Scheme 68

Flow Chart A3 (1 of 3), Cranks/Won't Run (3.8L W/ Type II Ignition System). Scheme 69

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.

Flow Chart A3 (1 of 3, Part 1), Cranks/Won't Run (3.8L W/ Type II Ignition System). Scheme 70

Flow Chart A3 (1 of 3, Part 2), Cranks/Won't Run (3.8L W/ Type II Ignition System). Scheme 71

Circuit Description For Steps 7-11 (2 Of 3, 3.8L Non-Turbo With Type II Ignition System)

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.

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/Won't Run (3.8L W/ Type II Ignition System). Scheme 72

Flow Chart A3 (2 of 3). Scheme 73

Circuit Description - Steps 12-14 (3 Of 3, 3.8L Non-Turbo With Type II Ignition System)

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.

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/Won't Run (3.8L W/ Type II Ignition System). Scheme 74

Flow Chart A3 (3 of 3). Scheme 75

CHART A3 - ENGINE CRANKS BUT WON'T RUN (3.8L TURBO)

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. The following step numbers refer to the numbers in the accompanying flow chart.

1. Light "ON" is a check for battery and ignition voltage to the 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. 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. Checks to see if the ECM is receiving a reference signal from the 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.

Flow Chart A3, Engine Cranks But Won't Run (3.8L Turbo). Scheme 76

Flow Chart A3, Engine Cranks But Won't Run (3.8L Turbo). Scheme 77

CHART A5 - FUEL SYSTEM ELECT. TEST (3.0L VIN L, "N" BODY)

When the ignition is turned on, the ECM will energize the fuel pump relay which completes the circuit to the in-tank fuel pump. It will remain on as long as the engine is cranking or running, and the ECM is receiving ignition reference pulses. If there are no reference pulses, the ECM will de-energize the fuel pump relay within 2 seconds after ignition is turned on, or the engine is stopped.

The fuel pump will deliver fuel to the fuel rail and injectors and then to the pressure regulator, where the system pressure is controlled. Excess fuel pressure is by-passed back to the fuel 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 the test terminal. Improper fuel system pressure may contribute to one or all of the following symptoms

1. Cranks, but won't run.
2. Code 44 or 45.
3. Cuts out, may feel like ignition problems.
4. Hesitation, loss of power and poor fuel economy.

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

Scheme 78

Scheme 79

1. If the fuse is blown, a short to ground in circuits No. 120, 939, or the fuel pump itself is the cause.
2. Determines if the fuel pump circuit is being controlled by the ECM. The ECM should energize the fuel pump relay. Since engine is not cranking or running, ECM should de-energize the relay within 2 seconds after ignition is turned on.
3. Turns on the fuel pump if circuit No. 120 wiring is okay. If the pump runs, it is a basic fuel delivery problem.
4. This test will determine if a short to ground on circuit No. 120 caused the fuse to blow. To prevent a misdiagnosis, be sure the fuel pump is disconnected before the test.
5. Checks for a short to ground in the fuel pump relay harness circuit No. 939. (Scheme 78): Chart A5, Schematic (Scheme 79): Chart A5, Fuel System Elect. Test (3.0L "N" Body, 1 of 2)
6. Checks for open in relay ground circuit No. 450.
7. Determines if the ECM is in control of the fuel pump relay through circuit No. 465.
8. The fuel pump control circuit includes an engine oil pressure switch with a separate set of normally open contacts. The switch closes at about 4 psi (.28 kg/cm 2 ) of oil pressure and provides a second battery feed path to the fuel pump. If the relay fails, the pump will continue to run using the current supplied by the closed oil pressure switch. This test checks the oil pressure switch to ensure it provides power to the fuel pump should the pump relay fail.
9. If the fuel pump relay control coil resistance is less than 20 ohms (shorted), repeat ECM failures may result.

A failed fuel pump relay will result in extended engine crank time, because of the time required to build enough oil pressure to close the oil pressure switch and turn on the fuel pump. There may be instances when the relay has failed but the engine will not crank fast enough to build enough oil pressure to close the switch. This, or a faulty relay in conjunction with a faulty oil pressure switch, can result in "Engine Cranks But Won't Run".

Chart A5, Fuel System Elect. Test (3.0L "N" Body, 2 of 2). Scheme 80

CHART A5 - FUEL SYSTEM ELECTRICAL TEST (3.8L)

When the ignition is turned on, ECM will energize the fuel pump relay which completes the circuit to the in-tank fuel pump. It will remain on as long as the engine is cranking or running, and the ECM is receiving ignition reference pulses. If there are no reference pulses, ECM will de-energize the fuel pump relay within 2 seconds after ignition is on, or the engine is stopped.

The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator. The fuel pump test terminal is located in the engine compartment. Pump can be turned on by applying battery voltage to the test terminal. Improper fuel system pressure may contribute to one or all of the following symptoms

1. Cranks but won't run.
2. Code 44 or 45.
3. Cuts out, may feel like ignition problem.
4. Hesitation, loss of power

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

1. If the fuse is blown, a short to ground in circuits No. 120, 839 or the fuel pump itself is the cause.
2. Determines if the fuel pump circuit is being controlled by the ECM. The ECM should energize the fuel pump relay. The engine is not cranking or running as the ECM should de-energize the relay within 2 seconds after ignition is turned on.
3. Turns on the fuel pump if circuit No. 120 wiring is okay. If the pump runs, it is a basic fuel delivery problem.
4. This test will determine if a short to ground on circuit No. 120 caused the fuse to blow. To prevent a misdiagnosis, be sure the fuel pump is disconnected before the test.
5. Checks for a short to ground in the fuel pump relay harness (circuit No. 839).
6. Checks for open in the relay ground, circuit No. 450 (terminal "C").
7. Determines if the ECM is in control of the fuel pump relay through circuit No. 465 (relay terminal "A").
8. The fuel pump control circuit includes an engine oil pressure switch with a separate set of normally open contacts. Switch closes at about 4 psi (.28 kg/cm 2 ) of oil pressure and provides a second battery feed path to the fuel pump. If relay fails, pump will continue to run using the battery feed supplied by the closed oil pressure switch. This test checks the oil pressure switch to be sure it provides battery feed to the fuel pump should the pump relay fail.
9. If the fuel pump relay control coil resistance is less than 20 ohms (shorted), repeated ECM failures may result.

A failed fuel pump relay will result in extended engine crank time, because of the time required to build enough oil pressure to close the oil pressure switch and turn on the fuel pump. There may be instances when the relay has failed but the engine will not crank fast enough to build enough oil pressure to close the switch. This or a faulty oil pressure switch can result in "Cranks But Won't Run".

Flow Chart A5, Fuel System Elect. Test (3.8L A/C/G & H Bodies, 1 of 2). Scheme 81

Flow Chart A5, Fuel System Elect. Test (3.8L A/C/G & H Bodies, 1 of 2). Scheme 82

Flow Chart A5, Fuel System Elect. Test (3.8L A/C/G & H Bodies, 2 of 2). Scheme 83

Flow Chart A5, Fuel System Elect. Test (3.8L A/C/G & H Bodies, 2 of 2). Scheme 84

CHART A7 - FUEL PRESSURE TEST - ALL ENGINES

The fuel pump will deliver fuel to the fuel rail and injectors and then to the pressure regulator, where the system pressure is controlled. Excess fuel pressure is by-passed back to the fuel tank. The fuel pump test terminal is located in the engine compartment. Fuel pump can be turned on by applying battery voltage to the test terminal.

Improper fuel system pressure may contribute to one or all of the following symptoms

1. Cranks but won't run.
2. Code 44 or 45.
3. Cuts out, may feel like ignition problem.
4. Hesitation, loss of power, or poor fuel economy.

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

1. Install Fuel Pressure Gauge (J-34730-1). Wrap a shop towel around the fuel pressure gauge tap to absorb fuel leakage that may occur when installing the gauge. With ignition on, pump pressure should be 34-40 psi (2.3-2.8 kg/cm 2 ) for 3.8L and 40-47 psi (2.8-3.2 kg/cm 2 ) for 3.0L. This pressure is controlled by spring pressure and manifold vacuum within the pressure regulator assembly. Pressure should not leak down after the fuel pump is shut off.
2. When the engine is idling, the vacuum is high and is applied to the fuel regulator diaphragm. This will overcome regulator spring pressure, resulting in a lower fuel pressure of 25-35 psi (1.7-2.4 kg/cm 2 ) on 3.8L and 31-42 psi (2.1-2.9 kg/cm 2 ) on 3.0L.
3. The application of 12-14 in. Hg vacuum to the pressure regulator should result in less fuel pressure.
4. Pressure that leaks down may be caused by one of the following conditions: In-tank fuel pump check valve not holding. Pump coupling hose leaking. Fuel pressure regulator valve leaking. Injector sticking open. NOTE: Refer to TROUBLE SHOOTING in article FUEL INJ - MULTI-PORT in the ENGINE PERFORMANCE section.
5. If fuel system has pressure but is less than specifications, condition may be caused by one of the following: Regulated Pressure, But Less Than Specifications The amount of fuel to injectors is okay but pressure is too low. The fuel system will be running lean and may set Code 44. Vehicle may also exhibit hard starting cold and overall poor performance. Restricted Fuel Flow Causing Pressure Drop Normally, a vehicle with fuel pressure of less than 24 psi (1.7 kg/cm 2 ) at idle will not be driveable, however, if the pressure drop occurs only while driving, the engine will normally surge then stop as pressure begins to drop rapidly.
6. Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to the pump test terminal, pressure should be greater than 75 psi (5.2 kg/cm 2 ).
7. This test determines if the high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.

Chart A7, Schematic. Scheme 85

Flow Chart A7, Fuel Pressure Test All Engines (1 of 2). Scheme 86

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

Flow Chart A7, Fuel Pressure Test All Engines (1 of 2). Scheme 87

Flow Chart A7, Fuel Pressure Test All Engines (2 of 2). Scheme 88

CHART B1 - RESTRICTED EXHAUST SYSTEM CHECK

Before any components are replaced, exhaust system must be checked for restrictions. Check at AIR pipe or check at O2 sensor procedure may be used to diagnose condition, depending on engine or tool used.

Check At Air Pipe

Remove rubber hose at exhaust manifold AIR pipe check valve and remove check valve. Install fuel pump pressure gauge to hose and nipple via Propane Enrichment Device (J26911) (Scheme 89)and (Scheme 90). Nipple should be inserted into exhaust manifold AIR pipe.

Flow Chart B1, Restricted Exhaust System Check (1 of 2). Scheme 89

Flow Chart B1, Restricted Exhaust System Check (2 of 2). Scheme 90

Check At O2 Sensor

Remove O2 sensor. Install backpressure tester in place of O2 sensor as shown in illustration. After test is completed, be sure to coat sensor threads with anti-seize compound before installation.

Diagnosis

1. Start engine and bring to operating temperature. Allow engine to idle and observe exhaust system backpressure gauge. Reading should not exceed 1.25 psi (.09 kg/cm 2 ).
2. Increase engine speed to 2000 RPM and note gauge. Reading should not exceed 3 psi (.21 kg/cm 2 ).
3. If during steps 1) or 2), specification is exceeded, exhaust system restriction is indicated.
4. Check complete exhaust system for collapsed pipe, heat distress and possible internal muffler failure.
5. If none of the conditions in step 4) exist, check for restricted catalytic converter. Replace if necessary.

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 (CARBURETOR)

ECM QDR IDENTIFICATION (PFI)

ECM QDR IDENTIFICATION (TBI)

ECM QDR IDENTIFICATION (TBI)

Scheme 91

CHART C1A - PARK/NEUTRAL SWITCH

The Park/Neutral (P/N) switch contacts are a part of the neutral start switch and are closed to ground in Park or Neutral, and open in Drive. The ECM supplies ignition voltage through a current limiting resistor to circuit No. 434 and senses a closed switch when the voltage on circuit No. 434 drops to less than one volt. The ECM uses the P/N signal as one of the inputs to idle air control and VSS diagnostics.

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

1. This test checks for a closed switch to ground in Park position. Different makes of "Scan" tester will display P/N status differently. Refer to owners manual for display used.
2. This test checks for an open switch in Drive.
3. Be sure "Scan" tester indicates Drive, even while wiggling shifter. This will test for an intermittent condition due to an faulty or misadjusted P/N switch.

Chart C1A, Schematic. Scheme 92

Flow Chart C1A, Park/Neutral Switch. Scheme 93

Flow Chart C1A, Park/Neutral Switch. Scheme 94

CHART C1E - POWER STEERING PRESSURE SWITCH CHECK

The Power Steering Pressure Switch (PSPS) opens when power steering pressure goes high, such as on a full turn in either direction. When the PSPS switch opens, it turns the A/C relay off and sends a signal to the ECM. The ECM uses this signal for idle control.

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

1. This test checks to see that P/S pressure switch opens when pressure goes high.
2. Checks to see that P/S pressure switch is closed.

Chart C1E, Schematic. Scheme 95

Flow Chart C1E, Power Steering Pressure Switch (PSPS) Check. Scheme 96

Flow Chart C1E, Power Steering Pressure Switch (PSPS) Check. Scheme 97

CHART C2A - INJECTOR BALANCE TEST

Note. If it is determined that injectors are dirty, they should be cleaned using approved injector cleaning procedures prior to performing this test. Complete CHART A7 - FUEL PRESSURE TEST before starting this test.

The injector balance test is used to pulse the injector for a precise amount of time, spraying a measured amount of fuel in the intake manifold. As each injector is pulsed, a drop in fuel rail pressure occurs. This pressure drop can be recorded and compared to other injectors. An injector that has a pressure drop difference of 1.5 psi (.11 kg/cm 2 ) or more, greater or less than other injectors, should be considered faulty.

Note. Allow engine to cool down to avoid irregular readings due to "Hot Soak" fuel boiling. In order to prevent flooding, the INJECTOR BALANCE TEST should not be repeated more than once, without starting and running engine.

1. With ignition off, connect Fuel Pressure Gauge (J34730-1) to pressure tap. Unplug harness connector at all injectors. Connect Injector Tester (J34730-3) to one of the injectors. On turbocharged engines, use adapter harness supplied with injector tester to pulse injectors that are not accessible.
2. Follow manufacturer's instructions for use of the adapter harness. Ignition should be turned off for at least 10 seconds to complete ECM shutdown cycle.
3. Turn ignition on. Fuel pump should run at least 2 seconds after ignition is turned on. Bleed air from gauge and hose to ensure accurate gauge reading. Repeat this procedure until all air is bled from system. Turn ignition off for at least 10 seconds.
4. Turn ignition on again to bring fuel pressure to maximum. Record initial pressure reading. Energize tester one time and note pressure drop at lowest point.
5. Disregard any slight pressure drop after low point is reached. Subtracting second pressure reading from initial reading indicates amount of injector pressure drop.
6. Repeat test step 4) on each injector and compare amount of pressure drop. Recheck injectors that do not read within pressure drop range. Replace injector(s) that fail second check.
7. If injectors are all okay, plug in harness connectors and review SYMPTOMS in TROUBLE SHOOTING section.

Flow Chart C2A, Injector Balance Test. Scheme 98

CHART C2C - IDLE AIR CONTROL

The ECM controls idle RPM using the IAC valve. To increase idle RPM, the ECM retracts the IAC, allowing more air to pass around the throttle plate. To decrease RPM, it extends the IAC valve, reducing airflow around the throttle plate. The "Scan" tester will read the ECM commands to the IAC valve in counts (0-255). The greater the counts, the more air allowed (higher idle). The less the counts, the less air allowed (lower idle).

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

1. Continue with test, even if engine will not idle. If idle is too low, "Scan" tester will display 80 or more counts, or steps. If idle is high, it will display zero counts. Occasionally an erratic or unstable idle may occur. If engine speed varies 200 RPM or more up and down, disconnect IAC. If the condition is unchanged, the IAC is not at fault.
2. When the engine was stopped, the IAC valve retracted (more air) to a fixed "Park" position for increased airflow and idle speed during the next engine start. A "Scan" tester will display 100 or more counts.
3. Be sure to disconnect the IAC valve prior to this test. The test light will confirm the ECM signals by a steady or flashing light on all circuits.
4. There is a remote possibility that one of the circuits is shorted to voltage, which would have been indicated by a steady light. Disconnect ECM and turn the ignition on and probe terminals to check for this condition.

A slow instable idle may be caused by a system problem than cannot be overcome by the IAC. The "Scan" tester counts will be greater than 60 counts if too low, and zero counts if too high.

If idle is too high, stop engine. With ignition on, ground diagnostic terminal and wait 30 seconds for IAC to seat, then, disconnect IAC. Unground diagnostic terminal and start engine. If idle speed is more than 750-850 RPM, locate and correct vacuum leak. For other causes of an improper idle, check the following

1. System Too Lean Idle speed may be too high or too low or engine running speed may vary up and down, disconnecting the IAC does not help. May set a Code 44. The "Scan" tester will read an oxygen sensor output less than .3 volt. Check for low regulated fuel pressure or water in fuel. A lean exhaust, with an oxygen sensor output fixed greater than .8 volts, will be a sensor contaminated with silicone.
2. System Too Rich Idle speed too low. "Scan" tester counts will be usually greater than 80. System is obviously rich and may exhibit Black exhaust smoke. The "Scan" tester will read an oxygen sensor signal fixed greater than .8 volt. Check for high fuel pressure or injector leaking or sticking.
3. Throttle Body Remove IAC and inspect for foreign material or evidence of IAC valve dragging the bore.

Chart C2C, Schematic. Scheme 99

Flow Chart C2C, Idle Air Control. Scheme 100

Flow Chart C2C, Idle Air Control. Scheme 101

CHART C3 - CANISTER PURGE CHECK

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).

The purge solenoid is energized (purge on) if the diagnostic test terminal is grounded with the engine stopped or if following conditions are met

1. Engine run time is more than one minute.
2. Coolant temperature more than 176°F (80°C).
3. Vehicle speed more than 5 MPH
4. Throttle position voltage greater than .75 volt.

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

1. Checks to see if the solenoid is opened or closed. The solenoid is normally de-energized in this test, so it should be closed.
2. This test completes functional check by grounding test terminal. This should normally energize the solenoid and allow the vacuum to drop (purge on).
3. This test checks for open or shorted 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 ECM failure. Using an ohmmeter, check the purge solenoid and coolant fan relay resistance, before installing a replacement ECM. This could cause a failure of the purge circuit.
5. Checks to see if short to voltage damaged original ECM.

Chart C3, Schematic. Scheme 102

Flow Chart C3, Canister Purge Check. Scheme 103

Flow Chart C3, Canister Purge Check. Scheme 104

CHART C4E - 3.8L TYPE I IGNITION

Note. Test numbers refer to test number on diagnostic charts.

1. Verification of TYPE I and TYPE II ignition systems is very important, because TYPE I diagnostics chart will not work on TYPE II system. See Diagnostic Chart for TYPE I or TYPE II ignition systems. If a plug wire is open, the other plug on the coil may still fire at idle. This tests the ability of the system to produce at least 25,000 volts.
2. No spark on one cylinder may be caused by an open plug wire or secondary winding. Both wires related to a coil and the secondary winding resistance should be checked. Resistance readings over the upper limit but not infinite will probably not cause a no start, but may cause an engine miss under certain conditions.
3. This test checks the triggering circuit in the ignition module. A blinking light indicates the module is triggering. The schematic shows the control wire color for each coil. Before checking the primary winding, check and note the resistance of the ohmmeter leads by touching them together.
4. This test determines whether the ECM is seeing camshaft and/or crankshaft sensor signals. If the test light blinks, the ECM is receiving good camshaft and/or crankshaft signals, so the problem is a faulty module connection or module.
5. This test provides the ECM with a substitute camshaft signal.
6. This test checks the crankshaft sensor signal. The ECM must see a camshaft sensor signal first, before it will recognize the crankshaft sensor signal. Jumping the camshaft sensor first, is very important in making an accurate test at this point.
7. This signal is supplied by the module and is pulled low each time the crankshaft signal occurs.
8. This checks for the battery voltage supplied by the module to operate the sensor.
9. This test checks to see if problem is in ground circuit No. 642, or power circuit No. 643 or ignition module.
10. See INTRODUCTION.

Chart C4E, Schematic. Scheme 105

Flow Chart C4E, 3.8L Type I Ignition (1 of 2). Scheme 106

Flow Chart C4E, 3.8L Type I Ignition (1 of 2, Part 1). Scheme 107

Flow Chart C4E, 3.8L Type I Ignition (1 of 2, Part 2). Scheme 108

Flow Chart C4E, 3.8L Type I Ignition (2 of 2). Scheme 109

Flow Chart C4E, 3.8L Type I Ignition (2 of 2). Scheme 110

CHART C4F - 3.8L TYPE II IGNITION

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

1. Verification of TYPE I and TYPE II ignition system is very important, because TYPE I diagnostic chart will not work on TYPE II system. See Diagnostic Chart for TYPE I or TYPE II ignition systems. If a plug wire is open, the other plug on the coil may still fire at idle. This tests the ability of the system to produce at least 25,000 volts.
2. No spark on one cylinder may be caused by an open plug wire or secondary winding. Both wires related to a coil and the secondary winding resistance should be checked. Resistance readings over the limit but not infinite will probably not cause a no start, but may cause an engine miss under certain conditions.
3. This test checks the triggering circuit in the ignition module. A blinking light indicates the module is triggering.
4. A slow blinking at this point indicates that the ECM is not seeing a crankshaft sensor signal.
5. At this point the camshaft sensor and its control have proved to be good. The problem is in the crankshaft sensor, sensor circuits or the ignition module.
6. Turn ignition on and listen for fuel pump within first two seconds. If fuel pump runs, the fuse is okay.
7. Check to see if problem is a grounded crankshaft sensor signal circuit or a camshaft sensor circuit fault.
8. The ignition module supplies the power to operate the camshaft sensor. This test checks to see if problem is the module or harness.
9. Test one checked the fuse. This test determines if problem is in circuit No. 939 from the fuse or a faulty ignition module.
10. See INTRODUCTION.

Flow Chart C4F, 3.8L Type II Ignition (1 of 2). Scheme 111

Flow Chart C4F, 3.8L Type II Ignition (1 of 2, Part 1). Scheme 112

Flow Chart C4F, 3.8L Type II Ignition (1 of 2, Part 1). Scheme 113

Flow Chart C4F, 3.8L Type II Ignition (2 of 2). Scheme 114

Flow Chart C4F, 3.8L Type II Ignition (2 of 2). Scheme 115

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 its 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 C4F1 Schematic, C3I Misfire At Idle (3.0L VIN L). Scheme 116

Flow Chart C4F1, C3I Misfire At Idle (3.0L VIN L). Scheme 117

Flow Chart C4F1, C3I Misfire At Idle (3.0L VIN L). Scheme 118

Test Description For Steps 1-5 (3.8L VIN's 3 & 7)

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 its 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 (3.8L 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.

Test Description For Steps 1-4 (3.0L VIN L & 3.8L VIN's 3 & 7)

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 its 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 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.

C4F2 Schematic, C3I Misfire Under Load (3.8L VINs 3 & 7). Scheme 119

Flow Chart C4F2, C3I Misfire Under Load (All 3.0L & 3.8L). Scheme 120

CHART C4G - 3.8L TYPE I TURBO IGNITION

1. If a plug wire is open, the other plug on that coil may still fire at idle. This tests the ability of the system to produce at least 25,000 volts.
2. No spark on one cylinder may be caused by an open plug wire or secondary winding. Both wires related to a coil and the secondary winding resistance should be checked. Resistance readings over the limit but not infinite will probably not cause a no start, but may cause an engine miss under certain conditions.
3. This test checks the triggering circuit in the ignition module. A blinking light indicates the module is triggering. The schematic shows the control wire color for each coil. For example, if testing why No. 1 did not fire, connect the test light between the Blue feed wire and the Yel/Blk control wire. Before checking the primary winding, check and note the resistance of the ohmmeter leads by touching them together.
4. This test determines whether the ECM is seeing cam and crank sensor signals. If the test light blinks, the ECM is receiving good cam an crank signals, so the problem is a faulty module connection or module.
5. This test provides the ECM with a substitute cam signal.
6. This test checks the crank sensor signal circuit. The ECM must see a cam sensor signal first, before it will recognize the crank sensor signal. Jumping the cam sensor first, is very important in making an accurate test at this point.
7. This signal is supplied by the module and is pulled low each time the crank signal occurs.
8. This checks for the battery voltage supplied by the module to operate the sensor.
9. This test checks to see if problem is in ground circuit 642, power circuit 643 or ignition module.

CHART C5 - ELECTRONIC SPARK CONTROL

The Electronic Spark Control (ESC) system is comprised of a knock sensor and an ESC module. As long as the ESC module is sending a voltage signal (8-10 volts) to the ECM (no detonation detected by the ESC sensor) the ECM provides normal spark advance.

When the sensor detects detonation, the module turns off the circuit to the ECM and the voltage at ECM terminal "B7" drops to zero volts. The ECM then retards Electronic Spark Timing (EST) as much as 20 degrees to reduce detonation. This happens fast and frequently enough that if looking at this signal with a digital voltmeter (DVM), you won't see zero volts, but an average voltage somewhat less than what is normally seen with no detonation.

A loss of the knock sensor signal or a loss of ground at ESC module would cause the signal at the ECM to remain high. This condition would result in the ECM controlling EST as if no detonation were occurring. The EST would not be retarded, and detonation could become severe enough under heavy engine load conditions to result in pre-ignition and potential engine damage. Loss of the ESC signal to the ECM would cause the ECM to constantly retard ESC. This could result in sluggish performance and cause a Code 43 to set.

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

1. Tests ESC system's ability to detect detonation and retard the ignition timing.
2. By disconnecting the ESC module, the ECM monitors a low voltage at terminal "B7" and should retard the ignition timing.
3. After approximately 4 seconds, the "SERVICE ENGINE SOON" light will come on and Code 43 will be stored.
4. Checks for proper voltage output (measured on A/C scale) of knock sensor. Low or no voltage would indicate an open circuit to terminal "E" or a faulty sensor.
5. Checks to see if constant retard is due to a faulty knock sensor or module, or if a false voltage signal is being transmitted on the wire from the knock sensor by induction from an adjacent wire, such as a spark plug wire. Reroute wiring as necessary.

Chart C5, Schematic. Scheme 121

Flow Chart C5, Electronic Spark Control. Scheme 122

Flow Chart C5, Electronic Spark Control. Scheme 123

CHART C7 - EXHAUST GAS RECIRCULATION

The EGR valve is opened by solenoid-regulated manifold vacuum, to let exhaust gas flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion will be affected. For this reason, very little exhaust gas is allowed to pass through the valve, especially at idle. The EGR valve is usually open with engine at operating temperature and at speeds greater than idle. The amount of exhaust gas recirculated is controlled by variations in vacuum regulated by the ECM through the EGR vacuum control solenoid.

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

1. Checks for a sticking EGR valve. If sticking, remove and examine valve to determine whether it can be cleaned, or must be replaced. A sticking EGR valve will most likely cause a rough idle.
2. Checks for plugged EGR passages. If passages are plugged, the engine may have severe detonation on acceleration.

Chart C7, Schematic. Scheme 124

Flow Chart C7, Exhaust Gas Recirculation. Scheme 125

Flow Chart C7, Exhaust Gas Recirculation. Scheme 126

CHART C8 - TORQUE CONVERTER CLUTCH (3.0L "N" BODY)

The purpose of the Torque Converter Clutch (TCC) feature is to eliminate power loss when the vehicle is in a cruise condition. This allows the convenience of an automatic transmission and the fuel economy of a manual transmission.

Fused battery ignition is supplied to the TCC solenoid through the brake and 3rd gear switch. The ECM will engage TCC by grounding circuit No. 422 to energize the solenoid.

The TCC will engage when the following conditions occur

1. Engine warmed up to greater than 156°F (70°C).
2. Vehicle speed greater than about 45 MPH.
3. Throttle sensor output not changing, indicating a steady road speed.
4. 3rd gear switch closed.
5. Brake switch closed.

An engine coolant thermostat that is stuck open, or opens at too low a temperature, may result in an inoperative TCC.

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

1. When test light is off, this confirms 3rd gear switch is open.
2. At 30 MPH the 3rd gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding the diagnostic terminal with ignition on and engine off, should energize the TCC solenoid by grounding circuit No. 422. This test checks the capability of the ECM to supply a ground for the TCC solenoid.
4. Solenoids and relays are turned on or off by ECM internal electronic switches called "drivers". Each driver is part of a group of 4 called "quad-drivers". Failure of one can damage any other driver in the set. Before replacing ECM, be sure to check the coil resistance of all solenoids and relays controlled by the ECM. When checking TCC solenoid, be sure to raise drive wheels (support drive axles) and run about 30 MPH to close 3rd gear switch.

Chart C8, Schematic. Scheme 127

Flow Chart C8, Torque Converter Clutch (3.0L "N" Body). Scheme 128

If Using A "Scan" Tool, Check The Following And Correct If Necessary

1. Coolant Temperature
2. TPS
3. VSS
4. Codes - If 24 Is Present, See Code Chart 24

Also Perform Mechanical Checks, Such As Linkage, Oil Level, Etc., Before Using This Chart

Flow Chart C8, Torque Converter Clutch (3.0L "N" Body). Scheme 129

Torque Converter Clutch (TCC) (3.8L Non-Turbo, "A", "C", & H" Bodies)

The purpose of the Torque Converter Clutch (TCC) feature is to eliminate the power loss of the torque converter when the vehicle is in a cruise condition. This allows the convenience of an automatic and the fuel economy of a manual transaxle. The heart of the system is an ECM-controlled solenoid located inside the transaxle.

When the solenoid coil is energized, the torque converter clutch is applied, which results in straight through mechanical coupling from the engine to the wheels. When the transmission solenoid is deactivated, the torque converter clutch is released which allows the torque converter to operate in the conventional manner (fluidic coupling between engine and transmission). The TCC will engage when the following conditions occur

1. Engine warmed up.
2. Vehicle speed greater than 28 MPH.
3. Throttle position sensor output not changing, indicating a steady road speed.
4. Brake switch closed.

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

1. This test checks the continuity of the TCC circuit from the fuse to the ALDL connector.
2. When the brake pedal is released and the diagnostic terminal is grounded, the light should come back on and then go off. This tests circuit No. 422 and the TCC driver in the ECM.

The "Scan" tester only indicates when the ECM has turned on the TCC driver. This does not confirm that the TCC has engaged. To determine if TCC is functioning properly, monitor engine RPM. Engine RPM should decrease when the "Scan" tester indicates the TCC driver has turned on.

Chart C8A, Schematic. Scheme 130

Flow Chart C8A, TCC (3.8L "A", "C" & "H" Bodies, 1 of 2). Scheme 131

Using A "Scan" Tool Check The Following And Correct As Necessary

1. Coolant Temperature Should Be Above 65°C
2. TPS - Be Sure TPS Signal Is Not Erratic
3. VSS - Be Sure "Scan" Displays VSS With Drive Wheels Turning, If Code 24 Is Present, See Code Chart 24

Flow Chart C8A, TCC (3.8L "A", "C" & "H" Bodies, 1 of 2). Scheme 132

The 3rd gear switch in this vehicle is open in 3rd and 4th gear. The 4th gear switch is open in 4th gear, which allows for TCC when in 4th gear.

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

1. Some "Scan" testers display the state of these switches in different ways. Be familiar with the type of tester being used. Since both switches should be in the closed state during this test, the tester should read the same for either the 3rd or 4th gear switch.
2. Determines whether the switch or signal circuit is open. The circuit can be checked for an open by measuring the voltage (with a voltmeter) at the TCC connector. Voltage should be about 12 volts.
3. Because the switch should be grounded in this test, disconnecting the TCC connector should cause the "Scan" tester switch state to change.
4. The switch state should change when the vehicle shifts into 3rd gear.

If vehicle is road tested because of a TCC related problem, be sure the switch states do not change while in 4th gear, because the TCC will disengage. If switches change state, carefully check wire routing and connections.

Flow Chart C8B, TCC (3.8L "A", "C" & "H" Bodies, 2 of 2). Scheme 133

Checks Made In This Chart Will Not Prevent The TCC From Working, But Will Affect Engagement Or Disengagement Points

Flow Chart C8B, TCC (3.8L "A", "C" & "H" Bodies, 2 of 2). Scheme 134

Torque Converter Clutch (TCC) (3.8L Turbo "G" Body)

The purpose of the converter clutch feature is to eliminate the power loss of the torque converter when the vehicle is in a cruise condition. This allows the convenience of an automatic and the fuel economy of a manual transmission. The heart of the system is an ECM-controlled solenoid which is located inside the transmission.

When the solenoid coil is energized, the torque converter clutch is applied, which results in straight through mechanical coupling from the engine to the wheels. When the transmission solenoid is deactivated, the torque converter clutch is released which allows the torque converter to operate in the conventional manner (fluidic coupling between engine and transmission). The TCC will engage on a warm engine under road load, in 4th gear only.

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

1. A test light on indicates battery voltage and continuity through TCC solenoid is okay.
2. Vacuum hose on throttle shaft pin increases TPS signal so TCC will engage without excessive wheel speed. Without the hose, it would require vehicle speed in excess of 65 MPH to engage TCC.
3. Checks for vehicle speed signal to ECM. Voltage should vary from 2-9 volts.
4. Checks 3rd and 4th gear signal to ECM. Signals will not prevent TCC engagement, but could cause a change in engagement and disengagement speed points.
5. Solenoids and relays are turned on or off by ECM internal electronic switches called "drivers". Each driver is part of a group of 4 called "quad-drivers". Failure of one can damage any other driver within the set.

Note. Before replacing ECM, be sure to check the coil resistance of all solenoids and relays controlled by the ECM.

Chart C8, Schematic. Scheme 135

Flow Chart C8, Torque Converter Clutch (3.8L "G" Body). Scheme 136

Flow Chart C8, Torque Converter Clutch (3.8L "G" Body) (1 Of 2). Scheme 137

Flow Chart C8, Torque Converter Clutch (3.8L "G" Body) (2 Of 2). Scheme 138

CHART C10A - A/C CLUTCH (3.0L & 3.8L NON-TURBO)

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement .4 second after A/C is turned on. This allows the IAC adequate time to adjust engine RPM before the A/C clutch engages. The ECM also causes the relay to disengage the A/C clutch during wide open throttle operation. The A/C clutch control relay is energized when the ECM provides a ground path for circuit No. 366.

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

1. Checks that ECM is controlling A/C clutch control relay.
2. Checks operation of A/C cycling switch.
3. Checks for open circuit on either side of relay coil.

Chart C10A, Schematic. Scheme 139

Chart C10A, A/C Clutch Control (3.0L/3.8L Non-Turbo, 1 of 2). Scheme 140

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

1. Checks that there is battery voltage to the relay through circuit No. 67.
2. Substitutes for relay to determine if problem is in relay or in circuit No. 59, A/C clutch coil, high pressure switch or ground.
3. Checks for open in circuit No. 67 between cycling switch and A/C fuse, or open circuit No. 67 to relay.
4. Checks that "A/C on" signal is getting to ECM through circuit No. 67. A test light that is off at this time indicates circuit No. 67 is open between the cycling switch and the ECM.

Chart C10A, A/C Clutch Control (3.0L/3.8L Non-Turbo, 2 of 2). Scheme 141

CHART C10D - A/C CLUTCH CONTROL (3.8L TURBO "G" BODY)

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement .4 second after A/C is turned on. This allows the IAC to adjust engine RPM before the A/C clutch engages. The ECM also causes the relay to disengage the A/C clutch during wide open throttle operation. The A/C clutch control relay is energized when the ECM provides a ground path for circuit No. 959.

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

1. Checks that ECM is controlling A/C clutch control relay.
2. This test checks operation of A/C cycling switch.
3. This test checks for grounded circuit No. 959 to ECM. At this point, the test light should be off.
4. This test checks for open circuit on either side of relay coil.

Chart C10D, Schematic. Scheme 142

Chart C10D, A/C Clutch Control (3.8L Turbo "G" Body, 1 of 2). Scheme 143

CHART C10E - A/C CLUTCH CONTROL (3.8L TURBO "G" BODY)

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement .4 second after A/C is turned on. This allows the IAC to adjust engine RPM before the A/C clutch engages. The ECM also causes the relay to disengage the A/C clutch during wide open throttle operation. The A/C clutch control relay is energized when the ECM provides a ground path for circuit No. 959.

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

1. Check for battery voltage to relay through circuit No. 67.
2. Substitutes for relay to determine if problem is in relay or in circuit No. 59, A/C clutch coil, high pressure switch or ground.
3. Checks for open in circuit No. 67 between cycling switch and A/C fuse, or open circuit No. 67 to relay.
4. Check to see that A/C is on is getting to ECM circuit 67. A test light off at the time indicates circuit No. 67 is open between the cycling switch and the ECM.

Chart C10E, A/C Clutch Control (3.8L Turbo "G" Body, 2 of 2). Scheme 144

Chart C12A - Coolant Fan Check (3.0L VIN L, "N" Body)

The coolant fan is energized through a low speed, high speed fan relay. Power for the fan comes through the fusible link to terminal No. 1 on all relays. The relays are energized when current flows to ground through the activation of the A/C pressure, coolant temperature switches and/or the ECM.

1. Low Speed Relay The low speed relay is energized by the ECM or the A/C pressure switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 208°F (98°C) and vehicle speed is less than 45 MPH. The low speed relay is also energized through the A/C pressure switch through terminal "B" when refrigerant pressure reaches 150 psi (10.5 kg/cm 2 ).
2. High Speed Relay The high speed relay is energized by the A/C high pressure and coolant override switches. If the A/C refrigerant pressure reaches 275 psi (19.3 kg/cm 2 ), or the coolant temperature reaches 226°F (108°C), the high speed fan relay is energized. The ECM has no control of the high speed fan relay.

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

1. Grounding the diagnostic test terminal should cause the ECM to ground circuit No. 535 and the fan to run at low speed.
2. Grounding the temperature switch harness terminal will check circuit No. 536 and will also check the high speed fan and pusher fan (VO8) relay (if equipped).
3. Checks circuit No. 533 between the fan control relay terminal No. 4 and the motor. If the fan does not operate, circuit No. 533 is open.
4. This test checks to see if the temperature switch is grounding and is grounded when the light comes on. The switch should close at 226°F (108°C).
5. If the vehicle is equipped with A/C, the following test will check the high pressure switch and related wiring from the switch to the fan control relay. If poor A/C performance is noted, the A/C pressure switch should be checked by a qualified A/C repair person. The low speed fan should come on if high pressure exceeds 150 psi (10.5 kg/cm 2 ).

Chart C12A, Schematic. Scheme 145

Flow Chart C12A, Coolant Fan Check (3.0L "N" Body, 1 of 3). Scheme 146

Flow Chart C12A, Coolant Fan Check (3.0L "N" Body, 1 of 3). Scheme 147

Chart C12B - Fan On At All Times (3.0L VIN L, "N" Body)

The coolant fan is energized through a low speed, high speed fan relay. Power for the fan comes through the fusible link to terminal No. 1 on all relays. The relays are energized when current flows to ground through the fusible link to terminal No. 1 on all relays. The relays are energized when current flows to ground through the activation of the A/C pressure, coolant temperature switches, and/or the ECM.

1. Low Speed Relay The low speed relay is energized by the ECM or the A/C pressure switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 208°F (98°C) and vehicle speed is less than 45 MPH. The low speed relay is also energized through the A/C pressure switch through terminal "B" when refrigerant pressure reaches 150 psi (10.5 kg/cm 2 ).
2. High Speed Relay The high speed relay is energized by the A/C high pressure and coolant override switches. If the A/C refrigerant pressure reaches 275 psi (19.3 kg/cm 2 ) or the coolant temperature reaches 226°F (108°C) the high speed fan relay is energized. The ECM has no control of the high speed relay.

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

1. Check to see if circuit No. 535 is shorted to ground which would keep the relay grounded at all times.
2. Check to see if circuit No. 536 is shorted to ground. A light indicates the wire is shorted to ground and the following tests will isolate the short.
3. If the test light is off after disconnecting, the ECM is shorted internally. Before replacing the ECM, be sure to check the resistance value of low speed side of the fan control relay. Replace if resistance is less than 20 ohms. Also be sure that circuit No. 535 is not shorted to battery voltage, and check the resistance of the canister purge solenoid. Replace solenoid if less than 20 ohms.

Flow Chart C12B, Fan On At All Times (3.0L "N" Body, 2 of 3). Scheme 148

Flow Chart C12B, Fan On At All Times (3.0L "N" Body, 2 of 3). Scheme 149

Chart C12C - No Low Speed Fan (3.0L Vin L, "N" Body)

The coolant fan is energized through a low speed/high speed fan relay. Power to the fan comes through the fusible link on terminal No. 1 of all relays. The relays are energized when current flows to ground through the fusible link to terminal No. 1 on all relays. The relays are energized when current flows to ground through the activation of the A/C pressure switches, coolant temperature switches, and/or the ECM.

1. Low Speed Relay The low speed relay is energized by the ECM or the A/C pressure switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 208°F (98°C) and vehicle speed is less than 45 MPH. The low speed relay is also energized through the A/C pressure switch through terminal "B" when refrigerant pressure reaches 150 psi (150 kg/cm 2 ).
2. High Speed Relay The high speed relay is energized by the A/C high pressure and coolant override switches. If A/C refrigerant pressure reaches 275 psi (19.3 kg/cm 2 ), or the coolant temperature reaches 226°F (108°C), the high speed fan relay is energized. The ECM has no control of the high speed relay.

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

1. Checks for battery voltage at relay harness connector.
2. Jumpering terminals No. 1 and 4 by-passes the relay which should cause the fan to run if the fan motor and the wiring to the motor are good.
3. Grounding the test terminal should cause the ECM to ground circuit No. 535. At this point, the test light should light if the ECM is good and circuit No. 535 isn't open.
4. This checks for battery voltage and ground to the fan motor. A test light on at this point indicates a faulty fan motor connection or motor.

Flow Chart C12C, No Low Speed Fan (3.0L "N" Body, 3 of 3). Scheme 150

Flow Chart C12C, No Low Speed Fan (3.0L "N" Body, 3 of 3). Scheme 151

Chart C12A - Coolant Fan Check (1 Of 3, All 3.8L Except 3.8L Turbo "G" Body)

On "VO8" (heavy duty cooling) system, 2 coolant fans are energized through one low speed and 2 high speed relays. On standard cooling applications, one fan and one low speed relay are used.

Power for the fan motors comes through the fusible link to terminal No. 1 on all relays. Relays are energized when current flows to ground through the activation of A/C, coolant switches, and/or ECM.

1. Low Speed Relay The low speed relay is energized by the ECM or the A/C pressure fan switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 208°F (98°C). The low speed relay is also energized through the A/C pressure fan switch (terminal "B") when refrigerant pressure reaches 150 psi (10.5 kg/cm 2 ).
2. High Speed Relay The high speed relay is energized by the A/C high pressure fan switch and coolant temperature override switches. If the A/C refrigerant pressure reaches 275 psi (19 kg/cm 2 ), or the coolant temperature reaches 226°F (108°C), the high speed fan relay is energized. The ECM has no control of the high speed fan relay.
3. Optional High Speed Relay The optional high speed relay is energized by the A/C high pressure fan switch and coolant temperature override switch and/or the temperature switch. Relay is energized any time the standard high speed relay is energized. The ECM has no control of the optional high speed relay.

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

1. Grounding the diagnostic test terminal should cause the ECM to ground circuit No. 535 and the fan should run in low speed.
2. Grounding the temperature switch harness terminal will check circuit No. 536 and the high side portion of the fan control relay.
3. Separates and checks relay driver circuit and relay to fan circuit for open circuit or faulty relay.
4. This test checks to see if the temperature switch is grounding and is also grounded when the test light is on. The switch should close at 226°F (108°C).
5. The following steps will check the high pressure switches and related wiring from the switch to the fan control relay. If poor A/C performance is noted, the A/C pressure switches should be checked by a qualified A/C repair person. The low speed fan should come on if high pressure exceeds 260 psi (18.3 kg/cm 2 ).

Chart C12A, Schematic. Scheme 152

Flow Chart C12A, Coolant Fan Check (3.8L Non-Turbo, 1 of 3). Scheme 153

Flow Chart C12A, Coolant Fan Check (3.8L Non-Turbo, 1 of 3). Scheme 154

Chart C12B - Fan Always On (2 Of 3, All 3.8L Except 3.8L Turbo "G" Body)

On "VO8" (heavy duty cooling) system, 2 coolant fans are energized through one low speed and 2 high speed relays. On standard cooling applications, one fan and one low speed relay are used.

Power for the fan motors comes through the fusible link to terminal No. 1 on all relays. Relays are energized when current flows to ground through the activation of A/C, coolant switches, and/or ECM.

1. Low Speed Relay The low speed relay is energized by the ECM or the A/C pressure fan switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 208°F (98°C). The low speed relay is also energized through the A/C pressure fan switch (terminal "B") when refrigerant pressure reaches 150 psi (10.5 kg/cm 2 ).
2. High Speed Relay The high speed relay is energized by the A/C high pressure fan switch and coolant temperature override switches. If the A/C refrigerant pressure reaches 275 psi (19 kg/cm 2 ), or the coolant temperature reaches 226°F (108°C), the high speed fan relay is energized. The ECM has no control of the high speed fan relay.
3. Optional High Speed Relay The optional high speed relay is energized by the A/C high pressure fan switch and coolant temperature override switch and/or the temperature switch. Relay is energized any time the standard high speed relay is energized. The ECM has no control of the optional high speed relay.

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

1. Checks to see if circuit No. 535 is shorted to ground. This would keep the relay grounded at all times.
2. Checks to see if circuit No. 536 is shorted to ground. A light indicates the wire is shorted to ground. The following tests will isolate the short.
3. If the test light is off after disconnecting ECM CD connector, the ECM is shorted internally. Before replacing the ECM, check the resistance value of low speed side of the fan control relay. Replace if resistance is less than 20 ohms. Also, be sure the circuit No. 535 is not shorted to battery voltage. Check the resistance of the canister purge solenoid, and replace if less than 20 ohms.

Flow Chart C12B, Fan On All Times (3.8L Non-Turbo, 2 of 3). Scheme 155

Flow Chart C12B, Fan On All Times (3.8L Non-Turbo, 2 of 3). Scheme 156

Chart C12C - No Low Speed Fan (3 Of 3, All 3.8L Except 3.8L Turbo "G" Body)

On "VO8" (heavy duty cooling) system, 2 coolant fans are energized through one low speed and 2 high speed relays. On standard cooling applications, one fan and one low speed relay are used.

Power for the fan motors comes through the fusible link to terminal No. 1 on all relays. Relays are energized when current flows to ground through the activation of A/C, coolant switches, and/or ECM.

1. Low Speed Relay The low speed relay is energized by the ECM or the A/C pressure fan switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 208°F (98°C). The low speed relay is also energized through the A/C pressure fan switch (terminal "B") when refrigerant pressure reaches 150 psi (10.5 kg/cm 2 ).
2. High Speed Relay The high speed relay is energized by the A/C high pressure fan switch and coolant temperature override switches. If the A/C refrigerant pressure reaches 275 psi (19 kg/cm 2 ), or the coolant temperature reaches 226°F (108°C), the high speed fan relay is energized. The ECM has no control of the high speed fan relay.
3. Optional High Speed Relay The optional high speed relay is energized by the A/C high pressure fan switch and coolant temperature override switch and/or the temperature switch. Relay is energized any time the standard high speed relay is energized. The ECM has no control of the optional high speed relay.

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

1. Check for battery voltage at relay harness connector.
2. Jumpering terminals No. 1 and 4 by-passes the relay. This should cause the fan to run, if fan motor and wiring to the motor are okay.
3. Grounding the test terminal should cause the ECM to ground circuit No. 535. At this point, the test light should light, if the ECM is okay and circuit No. 535 isn't open.
4. This checks for battery voltage and ground to the fan motor. A test light on, at this point, indicates a faulty fan motor connection, motor connection or motor.

Flow Chart C12C, No Low Speed Fan (3.8L Non-Turbo, 3 of 3). Scheme 157

Flow Chart C12C, No Low Speed Fan (3.8L Non-Turbo, 3 of 3). Scheme 158

Chart C12A - 2-Speed Coolant Fan Check (3.8L Turbo "G" Body)

Two coolant fans are energized through a low speed, high speed and delay relay. Power for the fan motors comes through the fusible link to terminal No. 1 on all relays. The relays are energized when current flows to ground through the activation of the A/C, coolant switches, and/or the ECM.

1. Low Speed Relay The low speed relay is energized by the ECM or the A/C pressure fan switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 208°F (98°C) and vehicle speed is less than 45 MPH. The low speed relay is also energized through the A/C pressure fan switch (terminal "B") when refrigerant pressure reaches 150 psi (10.5 kg/cm 2 ).
2. High Speed Relay The high speed relay is energized by the A/C high pressure fan switch and coolant temperature override switches. If the A/C refrigerant pressure reaches 275 psi (19 kg/cm 2 ), or the coolant temperature reaches 226°F (108°C), the high speed fan relay is energized. The ECM has no control of the high speed fan relay.
3. Delay Relay The delay relay is energized by the temperature switch. If coolant temperature is 226°F (108°C) or greater when the ignition is turned off, timer relay is energized for 10 minutes, or until coolant temperature is less than 226°F (108°C). The 150 watt fan is the only fan that will run with ignition off.

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

1. Grounding the diagnostic test terminal should cause the ECM to ground circuit No. 535 and the fan should run in low speed.
2. Grounding the temperature switch harness terminal will check circuit No. 335 and the high side portion of the fan control relay.
3. Check circuit No. 533 between high speed relay terminal No. 4 and the motor. If fan does not operate, circuit No. 533 is open or motor is faulty.
4. With ignition off and temperature switch grounded, delay relay is activated. This will cause fan to turn on for up to 10 minutes after engine shutdown.
5. This test checks to see if the temperature switch is grounding and is also grounded when the test light is on. The switch should close at 226°F (108°C).
6. The following tests will check the high pressure switches and related wiring from the switch to the fan control relay. If poor A/C performance is noted, the A/C pressure switches should be checked by a qualified A/C repair person. The low speed fan should come on if high pressure exceeds 260 psi (18.3 kg/cm 2 ).

Chart C12A, Schematic. Scheme 159

Flow Chart C12A, 2-Speed Fan Check (3.8L Turbo, 1 of 3). Scheme 160

Flow Chart C12A, 2-Speed Fan Check (3.8L Turbo, 1 of 3, Part 1). Scheme 161

Flow Chart C12A, 2-Speed Fan Check (3.8L Turbo, 1 of 3, Part 2). Scheme 162

Chart C12B - Fan On At All Times (3.8L Turbo "G" Body)

Two coolant fans are energized through a low speed, high speed and delay relay. Power for the fan motors comes through the fusible link to terminal No. 1 on all relays. The relays are energized when current flows to ground through the activation of the A/C, coolant switches, and/or the ECM.

1. Low Speed Relay The low speed relay is energized by the ECM or the A/C pressure fan switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 208°F (98°C) and vehicle speed is less than 45 MPH. The low speed relay is also energized through the A/C pressure fan switch (terminal "B") when refrigerant pressure reaches 150 psi (10.5 kg/cm 2 ).
2. High Speed Relay The high speed relay is energized by the A/C high pressure fan switch and coolant temperature override switches. If the A/C refrigerant pressure reaches 275 psi (19 kg/cm 2 ), or the coolant temperature reaches 226°F (108°C), the high speed fan relay is energized. The ECM has no control of the high speed fan relay.
3. Delay Relay The delay relay is energized by the temperature switch. If coolant temperature is 226°F (108°C) or greater, when the ignition is turned off, timer relay is energized for 10 minutes, or until coolant temperature is less than 226°F (108°C). The 150 watt fan is the only fan that will run with the ignition off.

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

1. This test will separate the problem between the timer relay and the fan control relay.
2. Checks to see if circuit No. 535 is shorted to ground, which would keep the relay grounded at all times.
3. Checks to see if circuit No. 335 is shorted to ground. A light indicates the wire is shorted to ground and the following tests will isolate the short.
4. If the test light is off, the ECM is shorted internally. Before replacing the ECM, be sure to check the resistance value of the low speed fan control relay. Replace relay if resistance is less than 20 ohms. Also, be sure that circuit No. 535 is not shorted to battery voltage, and check the resistance of the canister purge solenoid. Replace solenoid if under 20 ohms.

Flow Chart C12B, Fan On At All Times (3.8L Turbo, 2 of 3). Scheme 163

Flow Chart C12B, Fan On At All Times (3.8L Turbo, 2 of 3). Scheme 164

Before replacing ECM use ohmmeter and check resistance of

1. Coolant Fan Relay
2. Canister Purge Solenoid

Replace where resistance measures less than 20 ohms.

Chart C12C - No Low Speed Fan (3.8L Turbo "G" Body)

Two coolant fans are energized through a low speed, high speed and delay relay. Power for the fan motors comes through the fusible link to terminal No. 1 on all relays. The relays are energized when current flows to ground through the activation of the A/C, coolant switches, and/or the ECM.

1. Low Speed Relay The low speed relay is energized by the ECM or the A/C pressure fan switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 208°F (98°C) and vehicle speed is less than 45 MPH. The low speed relay is also energized through the A/C pressure fan switch (terminal "B") when refrigerant pressure reaches 150 psi (10.5 kg/cm 2 ).
2. High Speed Relay The high speed relay is energized by the A/C high pressure fan switch and coolant temperature override switches. If the A/C refrigerant pressure reaches 275 psi (19 kg/cm 2 ), or the coolant temperature reaches 226°F (108°C), the high speed fan relay is energized. The ECM has no control of the high speed fan relay.
3. Delay Relay The delay relay is energized by the temperature switch. If coolant temperature is 226°F (108°C) or greater, when the ignition is turned off, timer relay is energized for 10 minutes, or until coolant temperature is less than 226°F (108°C). The 150 watt fan is the only fan that will run with the ignition off.

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

1. Check for battery voltage at relay harness connector.
2. Jumpering terminals No. 1 and 4 by-passes the relay, which should cause the fan to run if fan motor and wiring to the motor are okay.
3. Grounding the test terminal should cause the ECM to ground circuit No. 535. At this point, the test light should light if the ECM is okay, and circuit No. 535 isn't open.
4. This checks for battery voltage and ground to the fan motor. A test light on at this point indicates a faulty fan motor connection or motor.

Flow Chart C12C, No Low Speed Fan (3.8L Turbo, 3 of 3). Scheme 165

Flow Chart C12C, No Low Speed Fan (3.8L Turbo, 3 of 3). Scheme 166

Chart C12D - Coolant Fan Check (1 Of 3, A/C Equipped W/O Heavy Duty Cooling - 3.8L "A" Body)

Circuit Description - The coolant fan motor can be energized through two relays; a fan relay, or timer relay. Power for the coolant fan motor comes through the fusible link to both relays. The relays are energized when current flows to ground, through the activation of the A/C high pressure switch, temperature override switch, and/or the ECM.

Fan Relay - The fan relay is energized by the ECI, A/C high pressure switch and/or the temperature override switch. The ECI energizes the fan relay through terminal "D2", when coolant temperature reaches 98°C (208°F). The A/C high pressure switch energizes the fan relay when refrigerant pressure reaches 300 psi (2068 kPa).

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

1. Checks to see if coolant fan motor runs at all times with ignition "ON".
2. Grounding the test terminal in the ALDL 5 connector, should cause the ECI to ground CKT 535. At this point, the coolant fan motor should run.
3. Grounding the temperature override switch harness to ground should cause the fan relay to turn "ON" the coolant fan motor. If the coolant fan motor runs, the fan relay and CKT 335 to the temperature override switch are good.
4. Grounding the A/C high pressure switch terminal should cause the fan relay to close, turning "ON" the coolant fan motor, proving the fan relay and circuit are OK.
5. Checks to see if the temperature override switch operates correctly. Test light should come "ON" at about 108°C (226°F), and the "hot light", on the instrument panel should come "ON" above 116°C (241°F).
6. Checks to see if the fan timer relay works. With temperature override switch harness grounded and ignition "OFF", fan should run until ground jumper is removed.

Chart C12D, Schematic, Coolant Fan Check (A/C Equipped w/o Heavy Duty Cooling - 3.8L "A" Body). Scheme 167

Flow Chart C12D, Coolant Fan Check (3.8L "A" Body, 1 of 3). Scheme 168

Chart C12E - Coolant Fan Check (2 Of 3, A/C Equipped W/O Heavy Duty Cooling - 3.8L "A" Body)

Circuit Description - The coolant fan motor can be energized through two relays; a fan relay, or timer relay. Power for the coolant fan motor comes through the fusible link to both relays. The relays are energized when current flows to ground, through the activation of the A/C high pressure switch, temperature override switch, and/or the ECM.

Fan Relay - The fan relay is energized by the ECI, A/C high pressure switch and/or the temperature override switch. The ECI energizes the fan relay through terminal "D2", when coolant temperature reaches 98°C (208°F). The A/C high pressure switch energizes the fan relay when refrigerant pressure reaches 300 psi (2068 kPa).

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

1. This check bypasses the fan relay and applies B+ directly to the coolant fan motor through CKT 532. At this point, the coolant fan motor should run.
2. Checks to see if problem is the fan relay, wiring, or ECM.
3. Checks for presence of B+ to relay connector terminal "5".
4. Checks for presence of B+ to relay connector terminal "A".
5. Checks for an open ground or coolant fan motor circuit, then checks for an open in CKT 532, between fan relay and coolant fan motor or faulty coolant fan motor.

Flow Chart C12E, Coolant Fan Check (3.8L "A" Body, 2 of 3). Scheme 169

Chart C12F - Coolant Fan Check (3 Of 3, A/C Equipped W/O Heavy Duty Cooling - 3.8L "A" Body)

Circuit Description - The coolant fan motor can be energized through two relays; a fan relay, or timer relay. Power for the coolant fan motor comes through the fusible link to both relays. The relays are energized when current flows to ground, through the activation of the A/C high pressure switch, temperature override switch, and/or the ECM.

Fan Relay - The fan relay is energized by the ECI, A/C high pressure switch and/or the temperature override switch. The ECI energizes the fan relay through terminal "D2", when coolant temperature reaches 98°C (208°F). The A/C high pressure switch energizes the fan relay when refrigerant pressure reaches 300 psi (2068 kPa).

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

1. Checks for B+ at terminals "1" and "4" to the timer relay.
2. Checks to be sure CKT 639 does not have voltage when the ignition switch is "OFF". If CKT 639 has voltage, with the ignition "OFF", the timer relay will not turn the fan "ON".
3. Checks to be sure CKT 450 is a good ground.

Flow Chart C12F, Coolant Fan Check (3.8L "A" Body, 3 of 3). Scheme 170

Chart C12G - Coolant Fan On At All Times (A/C Equipped W/O Heavy Duty Cooling - 3.8L "A" Body)

Circuit Description - The coolant fan motor can be energized through two relays; a fan relay, or timer relay. Power for the coolant fan motor comes through the fusible link to both relays. The relays are energized when current flows to ground, through the activation of the A/C high pressure switch, temperature override switch, and/or the ECM.

Fan Relay - The fan relay is energized by the ECI, A/C high pressure switch and/or the temperature override switch. The ECI energizes the fan relay through terminal "D2", when coolant temperature reaches 98°C (208°F). The A/C high pressure switch energizes the fan relay when refrigerant pressure reaches 300 psi (2068 kPa).

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

1. This step will separate the problem as either the timer relay or the fan relay.
2. Checks for short to voltage in CKT 532.
3. Checks to see if CKT 535 is shorted to ground, which would keep the relay grounded at all times.
4. Checks to see if CKT 335 is shorted to ground. A light indicates the wire is shorted to ground and following the steps will isolate the short.
5. If the test light is "OFF" after disconnecting, the ECM is shorted internally.

Flow Chart C12G, Coolant Fan On At All Times (3.8L "A" Body). Scheme 171

Chart C12H - Coolant Fan Check (1 Of 3, A/C Equipped W/Heavy Duty Cooling - 3.8L "A" Body)

Circuit Description - On VO8 (heavy duty cooling) systems, the standard coolant fan motor and the VO8 fan motor are energized through a coolant fan relay and a VO8 fan relay and/or a coolant fan timer relay. Power for the coolant fan motors come through the fusible link to all relays. The relays are energized when current flows to ground through the activation of the A/C high pressure switch, temperature override switch and/or the ECM.

Coolant Fan Relay - The coolant fan relay is energized by the temperature override switch, A/C high pressure switch and/or the ECM. The ECM energizes the coolant fan relay through terminal "D2" when the coolant temperature reaches 98°C (208°F), and vehicle speed is below 45 mph. The relay is also energized through terminal "B" of the A/C high pressure switch (150 psi) and/or the temperature override switch (108°C).

VO8 Fan Relay - The pusher fan is installed as part of the heavy duty cooling package (VO8) and is turned "ON" when A/C system pressure reaches 275 psi (1896 kPa) or coolant temperature reaches 108°C (226°F).

Coolant Fan Relay - The coolant ran relay is energized by the temperature override switch. If the coolant temperature is 108°C (226°F) or higher when the ignition switch is turned "OFF", the timer relay is energized for 10 minutes or until the coolant temperature is lowered below 108°C (226°F). The standard coolant fan is the only fan that will run with the ignition switch "OFF".

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

1. Checks to see if fans run at all times with ignition "ON".
2. Grounding the test terminal, in the ALDL connector, should cause the ECM to ground CKT 535. At this point, the standard coolant fan should run.
3. Grounding the temperature override switch harness to ground should cause the relays to turn "ON" both fans. If the fans run, the fan control relays and CKT 335 to the temperature override switch are good.
4. Grounding each pressure switch terminal should cause relays to close, turning "ON" fans, proving relays and circuits are OK.
5. Checks to see if temperature override switch operates correctly. Test light should come "ON" at about 108°C (226°F), and the HOT light on the instrument panel should come "ON" above 116°C (241°F).
6. Checks to see if coolant fan relay works. With temperature override switch harness grounded, the coolant fan motor should run until ground jumper is removed.

Chart C12H, Schematic, Coolant Fan Check (A/C Equipped w/Heavy Duty Cooling - 3.8L "A" Body). Scheme 172

Flow Chart C12H, Coolant Fan Check (3.8L "A" Body, 1 of 3). Scheme 173

Chart C12I - Coolant Fan Check (2 Of 3, A/C Equipped W/Heavy Duty Cooling - 3.8L "A" Body)

Circuit Description - On VO8 (heavy duty cooling) systems, the standard coolant fan motor and the VO8 fan motor are energized through a coolant fan relay and a VO8 fan relay and/or a coolant fan timer relay. Power for the coolant fan motors come through the fusible link to all relays. The relays are energized when current flows to ground through the activation of the A/C high pressure switch, temperature override switch and/or the ECM.

Coolant Fan Relay - The coolant fan relay is energized by the temperature override switch, A/C high pressure switch and/or the ECM. The ECM energizes the coolant fan relay through terminal "D2" when the coolant temperature reaches 98°C (208°F), and vehicle speed is below 45 mph. The relay is also energized through terminal "B" of the A/C high pressure switch (150 psi) and/or the temperature override switch (108°C).

VO8 Fan Relay - The pusher fan is installed as part of the heavy duty cooling package (VO8) and is turned "ON" when A/C system pressure reaches 275 psi (1896 kPa) or coolant temperature reaches 108°C (226°F).

Coolant Fan Relay - The coolant ran relay is energized by the temperature override switch. If the coolant temperature is 108°C (226°F) or higher when the ignition switch is turned "OFF", the timer relay is energized for 10 minutes or until the coolant temperature is lowered below 108°C (226°F). The standard coolant fan is the only fan that will run with the ignition switch "OFF".

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

1. This check bypasses the coolant fan relay and applies B+ to the coolant fan motor through CKT 532. At this point, the fan should run.
2. Checks to see if problem is the coolant fan relay, wiring, or ECM.
3. Checks for presence of ignition voltage to relay connector terminal "5".
4. Checks for presence of B+ to coolant fan relay connector terminal "A".
5. Checks for an open ground or fan motor circuit, then checks for an open in CKT 532, between coolant fan relay and motor, or faulty motor.

Flow Chart C12I, Coolant Fan Check (3.8L "A" Body, 2 of 3). Scheme 174

Chart C12J - Coolant Fan Check (3 Of 3, A/C Equipped W/Heavy Duty Cooling - 3.8L "A" Body)

Circuit Description - On VO8 (heavy duty cooling) systems, the standard coolant fan motor and the VO8 fan motor are energized through a coolant fan relay and a VO8 fan relay and/or a coolant fan timer relay. Power for the coolant fan motors come through the fusible link to all relays. The relays are energized when current flows to ground through the activation of the A/C high pressure switch, temperature override switch and/or the ECM.

Coolant Fan Relay - The coolant fan relay is energized by the temperature override switch, A/C high pressure switch and/or the ECM. The ECM energizes the coolant fan relay through terminal "D2" when the coolant temperature reaches 98°C (208°F), and vehicle speed is below 45 mph. The relay is also energized through terminal "B" of the A/C high pressure switch (150 psi) and/or the temperature override switch (108°C).

VO8 Fan Relay - The pusher fan is installed as part of the heavy duty cooling package (VO8) and is turned "ON" when A/C system pressure reaches 275 psi (1896 kPa) or coolant temperature reaches 108°C (226°F).

Coolant Fan Relay - The coolant ran relay is energized by the temperature override switch. If the coolant temperature is 108°C (226°F) or higher when the ignition switch is turned "OFF", the timer relay is energized for 10 minutes or until the coolant temperature is lowered below 108°C (226°F). The standard coolant fan is the only fan that will run with the ignition switch "OFF".

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

1. Checks to be sure constant B+ is at terminals "1" and "4" to the timer relay.
2. Checks to be sure CKT 639 does not have voltage when the ignition switch is "OFF". If CKT 639 has voltage, with the ignition "OFF", the timer relay will not turn the fan "ON".
3. Checks to be sure CKT 450 is a good ground.

Flow Chart C12J, Coolant Fan Check (3.8L "A" Body, 3 of 3). Scheme 175

Chart C12K - Coolant Fan On At All Times (A/C Equipped W/Heavy Duty Cooling - 3.8L "A" Body)

Circuit Description - On VO8 (heavy duty cooling) systems, the standard coolant fan motor and the VO8 fan motor are energized through a coolant fan relay and a VO8 fan relay and/or a coolant fan timer relay. Power for the coolant fan motors come through the fusible link to all relays. The relays are energized when current flows to ground through the activation of the A/C high pressure switch, temperature override switch and/or the ECM.

Coolant Fan Relay - The coolant fan relay is energized by the temperature override switch, A/C high pressure switch and/or the ECM. The ECM energizes the coolant fan relay through terminal "D2" when the coolant temperature reaches 98°C (208°F), and vehicle speed is below 45 mph. The relay is also energized through terminal "B" of the A/C high pressure switch (150 psi) and/or the temperature override switch 108°C (226°F).

VO8 Fan Relay - The pusher fan is installed as part of the heavy duty cooling package (VO8) and is turned "ON" when A/C system pressure reaches 275 psi (1896 kPa) or coolant temperature reaches 108°C (226°F).

Coolant Fan Relay - The coolant ran relay is energized by the temperature override switch. If the coolant temperature is 108°C (226°F) or higher when the ignition switch is turned "OFF", the timer relay is energized for 10 minutes or until the coolant temperature is lowered below 108°C (226°F). The standard coolant fan is the only fan that will run with the ignition switch "OFF".

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

1. This step will separate the problem between the coolant fan timer relay or the coolant fan relay.
2. Checks for short to voltage in CKT 532 or 533.
3. Checks to see if CKT 335 or 535 is shorted to ground, which would keep the coolant fan relay grounded at all times.
4. Checks to see if CKT 335 is shorted to ground. A light indicates the wire is shorted to ground and the following steps will isolate the short.
5. If the test light is "OFF" after disconnecting, the ECM is shorted internally.

Flow Chart C12K, Coolant Fan On At All Times (3.8L "A" Body). Scheme 176

CODE 13 - OPEN OXYGEN (O2) SENSOR CIRCUIT

The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". If measured with 10-megohm digital voltmeter, this may read as low as .32 volt. The oxygen sensor varies the voltage within a range of about one volt if the exhaust is rich, down through about .10 volts if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is less than 600°F (360°C). An open sensor circuit or cold sensor causes "open loop" operation.

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

1. Code 13 will set if the following conditions occur: Engine is at operating temperature. Up to 2 minutes engine running time after start. Oxygen signal steady between .35 and .55 volt. Throttle position sensor signal greater than idle. All conditions must be met for 60 seconds. If all conditions for a Code 13 exist, system will not go into "closed loop".
2. This test will determine if the sensor or the wiring is the cause of a Code 13.
3. When performing this test, use only a high impedance (10-megohm) digital volt/ohmmeter. This test checks the continuity of circuits No. 412 and 413. If circuit No. 413 is open, the ECM voltage on circuit No. 412 will be greater than .6 volt.

An intermittent Code 13 may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Inspect ECM harness connectors for backed out terminals "D7 or "D6", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

If connections and harness checks out okay, "Scan" oxygen sensor voltage while moving related connectors and wiring harness. Engine should be warm, running at part throttle in "closed loop". If the failure is induced, the oxygen sensor voltage reading will change from its normal fluctuating voltage (greater than 600 mV to less than 300 mV) to a fixed value around 450 mV. This may help to isolate the location of the malfunction.

Schematic, Code 13: Open Oxygen (O2) Sensor Circuit. Scheme 177

Flow Chart, Code 13: Open Oxygen (O2) Sensor Circuit. Scheme 178

Flow Chart, Code 13: Open Oxygen (O2) Sensor Circuit. Scheme 179

Coolant Temperature Sensor (CTS) Signal Voltage Low

The coolant temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies and monitors a voltage on circuit No. 410 to the sensor. When the engine is cold the sensor resistance is high, therefore the ECM will see high monitored voltage.

As the engine warms, sensor resistance becomes less and monitored voltage drops. At normal engine operating temperature, voltage will measure about 1.5-2.0 volts.

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

1. Code 14 will set if monitored voltage indicates a coolant temperature greater than 275°F (135°C) for a certain length of time.
2. This test will determine if circuit No. 410 is shorted to ground, which will cause the conditions for Code 14.

The "Scan" tester displays engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C, then stabilize when thermostat opens.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check the following conditions

1. Poor Connection Inspect ECM harness connectors for backed out terminals "C10" or "D12", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittent If connections and harness checks out okay, use "Scan" tester to check the coolant temperature reading while moving related connectors and wiring harness. If the failure is induced, coolant temperature display will change. This may help to isolate the location of the malfunction.
3. Shifted sensor The TEMPERATURE-TO-RESISTANCE VALUES table may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a shifted (out-of-calibration) sensor which may result in driveability problems.

Schematic, Code 14, CTS Signal Voltage Low. Scheme 180

Flow Chart, Code 14, CTS Signal Voltage Low. Scheme 181

Flow Chart, Code 14, CTS Signal Voltage Low. Scheme 182

Coolant Temperature Sensor (CTS) Signal Voltage High

The coolant temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies and monitors a voltage on circuit No. 410 to the sensor. When the engine is cold, sensor resistance is high and the ECM sees a high monitored voltage. As the engine warms, the sensor resistance becomes less and monitored voltage drops. At operating temperature, voltage will measure about 1-2 volts at the ECM terminal.

Note. Test numbers refer to test numbers on diagnostic chart. The "Scan" tester reads engine temperature in degrees centigrade.

1. Code 15 will set if the monitored voltage indicates a coolant temperature less than -47°F (-44°C) for at least 3 seconds.
2. This test simulates a Code 14. If the ECM recognizes the low signal voltage, (high temperature) and the "Scan" tester reads 130°C, the ECM and wiring are okay.
3. Determines if circuit No. 410 is open. Using a digital volt/ohmmeter, there should be 5 volts present at sensor connector.

After engine is started the temperature should rise steadily to about 90°C, then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check the following conditions

1. Poor connection Inspect ECM harness connectors for backed out terminals "C10" or "D12", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittent If connections and harness check out okay, use "SCAN" tester to check coolant temperature while moving related connectors and wiring harness. If the failure is induced, the coolant temperature display will change. This may help to isolate the location of the malfunction.
3. Shifted sensor The TEMPERATURE-TO-RESISTANCE VALUE table may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a shifted (out-of-calibration) sensor which may result in driveability complaints.

A faulty connection, or an open circuit No. 410 or 452 will result in a Code 15. If Code 23 or 63 is also set, check circuit No. 452 for faulty wiring or connections. Check terminals at sensor for good contact.

Flow Chart, Code 14: CTS Signal Voltage High. Scheme 183

Flow Chart, Code 14: CTS Signal Voltage High. Scheme 184

CODE 21 - THROTTLE POSITION SENSOR 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 .4 volt at idle to 5 volts at wide open throttle.

The TPS signal is one of the most important inputs used by the ECM for fuel control and for most of the ECM control outputs.

Note. On 3.0L engines, letters "A" and "C" are reversed at TPS connector. Circuit locations, wire colors and ECM terminal numbers remain the same as 3.8L. Test numbers refer to test numbers on diagnostic chart.

1. Code 21 will set if the following conditions occur: Engine is running. TPS signal voltage is greater than 2.5 volts. Code 33 or 34 not present at first start up. All conditions met for 5 seconds. With closed throttle, ignition on or engine at idle, voltage should be less than .7 volt on 3.0L engine and .36-.44 volt on 3.8L engine. If voltage is not okay, check TPS adjustment.
2. With the TPS sensor disconnected, the TPS voltage should go low if the ECM and wiring is okay.
3. Probing circuit No. 452 with a test light checks the sensor ground circuit. A faulty sensor ground circuit will cause a Code 21.

An open in circuit No. 452 will result in a Code 21. Check the following conditions

1. Poor connection Inspect ECM harness connectors for backed out terminals "C13" and "D12", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittents If connections and harness checks out okay, monitor TPS voltage on "Scan" tester while moving related connectors and wiring harness. If the failure is induced, the coolant temperature display will change. This may help to isolate the location of the malfunction.
3. TPS scaling Observe TPS voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TPS voltage when throttle was closed, to greater than 4.5 volts when throttle is held at wide open throttle position.

Schematic, Code 21: TPS Signal Voltage High. Scheme 185

Flow Chart, Code 21: TPS Signal Voltage High. Scheme 186

Flow Chart, Code 21: TPS Signal Voltage High. Scheme 187

Throttle Position Sensor (TPS) Signal Voltage Low

The Throttle Position Sensor (TPS) provides a signal voltage that changes relative to throttle angle. Signal voltage will vary from about .4 volt at idle to about 5 volts at wide open throttle. The TPS signal is one of the most important inputs used by the ECM for fuel control and for most of the ECM control outputs.

Note. On 3.0L engine, letters "A" and "C" are reversed at TPS connector. Circuit locations, wire colors and ECM terminal numbers remain the same as 3.8L. Test numbers refer to test numbers on diagnostic chart.

1. Code 22 will set if engine is running and TPS signal voltage is less than .2 volt for 3 seconds.
2. Simulates Code 21. If ECM recognizes the high signal voltage, the ECM and wiring are okay.
3. With closed throttle, ignition on or engine at idle, voltage should be less than .7 volt on 3.0L engine and .36-.44 volt on 3.8L engine. If voltage is not okay, check TPS adjustment.
4. Simulates a high signal voltage. Checks circuit No. 417 for open.

The "Scan" tester reads throttle position in volts. Voltage should increase at a steady rate as throttle is moved from wide open throttle. Some testers may also read throttle angle in percent (zero at closed throttle, 100 at wide open throttle). An open or short to ground in circuit No. 416 or 417 will result in a Code 22. Check for the following conditions

1. Poor connections Inspect ECM harness connectors for backed out terminals "C13" and "D12", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittents If connections and harness checks out okay, monitor TPS voltage using "Scan" tester while moving related connectors and wiring harness. If the failure is induced, the coolant temperature display will change. This may help to isolate the location of the malfunction.
3. TPS scaling Observe TPS voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TPS voltage (or zero percent) when throttle was closed, to greater than 4.5 volts (or 100 percent) when throttle is held wide open.

Flow Chart, Code 22: TPS Signal Voltage Low. Scheme 188

Flow Chart, Code 22: TPS Signal Voltage Low. Scheme 189

Manifold Air Temperature (MAT) Sensor Signal Voltage High

The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies and monitors about 5 volts on circuit No. 472 to the sensor. When the air is cold, sensor resistance is high, therefore, the ECM will see a high monitored voltage. If the air is warm, the sensor resistance is low and ECM will see low monitored voltage. The MAT sensor is used in conjunction with the MAF sensor so the ECM can accurately compensate airflow readings based on temperature.

Code 23 will set if a signal voltage indicates a manifold air temperature less than -40°F (-40°C) for 4 seconds. Due to conditions necessary to set a Code 23, the "SERVICE ENGINE SOON" light will stay on only while the fault is present.

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

1. The "Scan" tester may not be used to diagnose this fault, due to the ECM transmitting "default" values. A Code 23 will set, due to an open sensor, wire or connection. This test determines if the wiring and ECM are okay.
2. If the resistance is greater than 25,000 ohms, replace the sensor.
3. Refer to AIRFLOW SENSING under OPERATION in article FUEL INJ - MULTI-PORT in the ENGINE PERFORMANCE section.

Schematic, Code 23: MAT Sensor Signal Voltage High. Scheme 190

Flow Chart, Code 23: MAT Sensor Signal Voltage High. Scheme 191

Flow Chart, Code 23: MAT Sensor Signal Voltage High. Scheme 192

CODE 24 - VEHICLE SPEED SENSOR

The Vehicle Speed Sensor (VSS) consists of a PM generator, buffer, speedometer and ECM. The PM generator is a permanent magnet assembly attached to the transmission or transaxle (in speedometer cluster on "A" body). As the vehicle moves, the generator creates a "sine wave" electrical pulse, which is routed to the buffer. In the buffer, the signal is changed from a "sine wave" to a "square wave" and amplified. The "square wave" is an on/off signal. The length of time between pulses determines vehicle speed. The ECM sends a 12-volt signal out on circuit No. 437. The frequency of the signal, which is pulsed low, is used by the ECM to determine vehicle speed.

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

1. Code 24 will set if vehicle speed equals zero MPH when the following conditions occur: Engine speed is between 1500 and 4000 RPM. TPS voltage reading shows closed throttle. Low load condition (low airflow). Not in Park or Neutral. All conditions met for 20 seconds.
2. Probe terminal "G" on "A" body. This test checks to see if the fault is circuit No. 437, including the ECM or the VSS/Buffer circuit. The ECM is the source of 12 volts via circuit No. 437 to the buffer in a normal working system.

Note. Disregard Code 24 that sets when the drive wheels are not turning.

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation.

Inspect ECM harness connector terminal "A10" for improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

If connections and harness check out okay, raise drive wheels (support drive axles to prevent damage to CV joints). Block other wheels and idle engine more than 3 MPH, in low gear. Use "Scan" tester to check the vehicle speed while moving related connectors and wiring harness. If the failure is induced, the vehicle speed display will change. This may help to isolate the location of the malfunction. A shorted cruise control module or a faulty or misadjusted Park/Neutral switch can result in a false Code 24.

Schematic, Code 24: Vehicle Speed Sensor. Scheme 193

Flow Chart, Code 24: Vehicle Speed Sensor. Scheme 194

Flow Chart, Code 24: Vehicle Speed Sensor. Scheme 195

Manifold Air Temperature (MAT) Sensor Signal Voltage Low

The ECM applies and monitors 4-6 volts on circuit No. 472 to the sensor. When manifold air is cold, the sensor (thermistor) resistance is high, therefore the ECM will see a high monitored voltage. As the air warms, the sensor resistance decreases and monitored voltage drops. Code 25 is set by the following

1. Signal voltage indicates manifold air temperature greater than 275°F (135°C).
2. Vehicle speed signal is present.
3. Both of the above requirements are met for at least 30 seconds. Due to conditions necessary to set a Code 23, the "SERVICE ENGINE SOON" light will stay on only while the fault is present.

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

1. The "Scan" tester may not be used to diagnose this fault, due to the ECM transmitting "default" values. ECM and wiring are good if voltage is greater than 4 volts.
2. If resistance is less than 100 ohms, replace sensor.
3. Refer to AIRFLOW SENSING under OPERATION in FUEL INJ - MULTI-PORT article in the ENGINE PERFORMANCE section.

Flow Chart, Code 25: MAT Sensor Signal Voltage Low. Scheme 196

Flow Chart, Code 25: MAT Sensor Signal Voltage Low. Scheme 197

CODE 31 - WASTEGATE SOLENOID (3.8L TURBO "G" BODY)

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 percent and no voltage pulses are received on the wastegate monitor. This condition must last more than 5 seconds.

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

1. Checks to see if circuit No. 928 is shorted to ground.
2. This test checks for an open circuit No. 928 to ECM. Grounding the test terminal should turn the test light on.
3. This test locates an open or short to voltage that could be the problem.

Schematic, Code 31: Wastegate Solenoid (3.8L "G" Body). Scheme 198

Flow Chart, Code 31: Wastegate Solenoid (3.8L "G" Body). Scheme 199

CODE 32 - EGR VACUUM CONTROL CIRCUIT

The EGR valve is opened by engine vacuum. In order to control and monitor EGR application an Electronic Vacuum Regulator Valve (EVRV) is used. The EVRV is composed of 2 devices: EGR solenoid (normally closed) and EGR vacuum switch (normally open).

The EGR vacuum is controlled when the ECM grounds circuit No. 435, energizing the EGR solenoid. ECM controls pulse width modulation by varying the vacuum source "on" time, as compared to "off" time. This is done thousands of times a second.

The EGR is monitored by the ECM through the EGR vacuum switch. The EGR vacuum switch (a normally open electrical switch) has an orifice which restricts the vacuum signal to the EGR vacuum switch. When sufficient vacuum reaches the EGR vacuum switch, the electrical switch closes. There should also be sufficient vacuum to open the EGR valve.

Code 32 will set if the vacuum switch closes at idle or does not close when engine is under a load (less than wide open throttle).

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

1. The "Scan" tester displays the condition of the EGR diagnostic switch. In Park or Neutral, the display should read "NO" or "OFF" (open switch).
2. Under moderate engine load, the display will switch from "NO" or "OFF" to "YES" or "ON".
3. This test checks the integrity of the 12-volt feed and ground circuits. If these circuits check okay, the fault is elsewhere in the EVRV/EGR control circuit.
4. A test light connected between terminals "A" and "B" will verify the integrity of the ECM wiring and check for proper ECM operation.
5. If the "Scan" tester displays "YES" or "ON" at engine idle, disconnect the EVRV harness. If display remains unchanged, the fault is either a short to ground in circuit No. 932 or the ECM.
6. If the EGR display switches from "YES" or "ON" to "NO" or "OFF" when the EVRV is disconnected, the fault is either in the EVRV/EGR solenoid, circuit No. 435 or the ECM. Probing at terminal "B" will further isolate the fault. If the test light is on, disconnect ECM "A" and "B" connector before checking circuit No. 435 for a short to ground since the short could be inside the ECM.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

1. Poor connection Inspect ECM harness connectors for backed out terminal "D6", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection or a damaged harness.
2. Intermittents If connections and harness checks out okay, use "Scan" tester to check the EVRV switch while moving related connectors and wiring harness. If the failure is induced, the EVRV switch display will change. This may help to isolate the location of the malfunction.

Flow Chart, Code 32: EGR Vacuum Control Circuit. Scheme 200

Flow Chart, Code 32: EGR Vacuum Control Circuit. Scheme 201

Schematic, Code 32: EGR Vacuum Control Circuit. Scheme 202

CODE 33 - MASS AIRFLOW (MAF) SENSOR

The Mass Airflow (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

1. Ignition on and airflow exceeds 20 grams per second. or the following conditions occur
2. Engine idling less than 800 RPM.
3. Throttle angle is 10 percent or less.
4. Airflow is more than 150 grams per second (high frequency).
5. All of the above conditions met for 5 seconds or more.

Note. The "Scan" tester is not of much use in diagnosing this code because when the code sets, ECM will display a default value. However, it may be useful in comparing the signal of a problem vehicle with that of a known good running one.

The MAF sensor produces a frequency signal, which cannot be easily measured. Check for the following

1. Poor connections Inspect ECM harness connectors for backed out terminal "B6". Check for broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection or a damaged harness.
2. Harness Inspect MAF sensor harness to ensure that it is not too close to high voltage wires, such as spark plug leads.
3. Intermittents If connections and harness check out, use "Scan" tester to check MAF while moving related connectors and wiring harness. If the failure is induced, the MAF display will change. This may help to isolate the location of the malfunction.

The MAF may be tested for calibration by using MAF Sensor Tester (J-36101). This tester will only indicate a sensor that is shifted completely from its calibrated frequency range.

Schematic, Code 33: Mass Airflow (MAF) Sensor. Scheme 203

Flow Chart, Code 33: Mass Airflow (MAF) Sensor. Scheme 204

Flow Chart, Code 33: Mass Airflow (MAF) Sensor. Scheme 205

CODE 34 - MASS AIRFLOW (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 following conditions exist

1. Engine is running with no MAF sensor signal. or the following conditions occur
2. Engine is running faster than 1400 RPM.
3. TPS signal more than 50 percent (2.5 volts).
4. Airflow is less than 10 grams per second (low frequency).
5. All of the above conditions have been met for more than 10 seconds.

Note. The "Scan" tester is not of much use in diagnosing this code because when the code sets, ECM will display a default value. However, it may be useful in comparing the signal of a problem vehicle with that of a known good running one.

The MAF sensor produces a frequency signal, which cannot be easily measured. Check for the following

1. Poor connections Inspect ECM pin "B6" and harness connectors for backed out terminals, improper connector mating, broken locks, improperly formed or damaged terminals and poor terminal-to- wire connection.
2. Harness Inspect MAF sensor harness to ensure that it is not too close to high voltage wires, such as spark plug leads.
3. Intermittents If harness appears okay, use "Scan" tester to check MAF while moving related connectors and wiring harness. A change in display would indicate the intermittent fault location.

The MAF sensor may be tested for being out of specification by using MAF Sensor Tester (J 36101). This tester will only indicate a sensor that is shifted completely from its calibrated frequency range.

Flow Chart, Code 34: Mass Airflow (MAF) Sensor. Scheme 206

Flow Chart, Code 34: Mass Airflow (MAF) Sensor. Scheme 207

Cam Sensor Signal (3.8L Non-Turbo VIN 3 & 3.8L Turbo VIN 7)

The cam sensor is a magnetic "Hall Effect" switch that provides the ECM with a voltage signal on the compression stroke of No. 1 cylinder. This information is used by the ECM to properly time the 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 one second. The engine will continue to run if the cam signal is lost while running, however, it will not restart after shutdown.

If the failure is in the cam signal output portion of the ignition module (terminal "J") or the cam sensor signal circuit No. 630 to ECM terminal "A11", the ECM will switch to the simultaneous fuel injection mode and continue to run. The engine can be re-started, but will continue to run in the simultaneous mode as long as the fault is present. In either failure mode, a Code 41 will be stored.

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

1. Checks to see if ECM recognizes a problem and sets Code 41. If the engine cranks but won't start, and a Code 41 was displayed, the fault is in the ignition system portion of the cam sensor circuit and should be diagnosed using CHART A3 - ENGINE CRANKS BUT WON'T RUN.
2. The voltage to ECM terminal "A11" is supplied by the ignition module. If voltage reading is less than 6 volts, the fault is in circuit No. 630, a poor connection at the ignition module, or a faulty ignition module.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following

1. Poor connection Inspect ECM harness connectors for backed out terminal "A11", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittents If connections and harness check out okay, monitor a digital voltmeter (10-megohm) connected from ECM terminal "A11" to ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change. This may help to isolate the location of the malfunction.

Schematic, Code 41: Cam Sensor Signal (3.8L VINs 3 & 7). Scheme 208

Flow Chart, Code 41: Cam Sensor Signal (3.8L VINs 3 & 7). Scheme 209

Flow Chart, Code 41: Cam Sensor Signal (3.8L VINs 3 & 7). Scheme 210

CODE 42 - EST IGNITION CIRCUIT

When the engine is cranking, the ignition module sends a reference signal to the ECM. While the engine speed is less than 400 RPM, the ignition module controls the ignition timing. When the engine speed exceeds 400 RPM, the ECM sends a 5-volt signal on the by-pass circuit No. 424 to switch the timing to ECM control circuit No. 423. An open or ground in the EST circuit stalls the engine and sets a Code 42. The engine can be re-started but will not run on module timing.

To set a Code 42 the following conditions must occur

1. Engine speed greater than 600 RPM with no EST pulse for 200 milliseconds (open or grounded circuit No. 423).

Or

1. ECM commanding by-pass mode (open or grounded circuit No. 424).

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

1. Checks to see if ECM recognizes a problem. If it doesn't set Code 42 at this point, it is an intermittent problem and could be due to a loose connection.
2. With the ECM disconnected, the ohmmeter should be reading less than 200 ohms, which is the normal resistance of the EST circuit through the ignition module. A higher resistance would indicate a fault in circuit No. 423, a poor ignition module connection, or a faulty ignition module.
3. If test light was on when connected from 12 volts to ECM harness terminal "D5", either circuit No. 423 is shorted to ground, or the ignition module is faulty.
4. Checks to see if ignition module switches when the by-pass circuit is energized by 12 volts through the test light. If the ignition module actually switches, the ohmmeter reading should shift to greater than 8000 ohms.
5. Disconnecting the ignition module should make the ohmmeter read as if it were monitoring an open circuit (infinite reading). Otherwise, circuit No. 423 is shorted to ground.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

1. Poor connection Inspect ECM harness connectors for backed out terminals "B4" or "D5", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittents If connections and harness checks out okay, monitor a digital voltmeter connected from the affected terminal to ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change.

Flow Chart, Code 42: EST Ignition Circuit. Scheme 211

Flow Chart, Code 42: EST Ignition Circuit. Scheme 212

CODE 43 - ELECTRONIC SPARK CONTROL

The Electronic Spark Control (ESC) system is comprised of a knock sensor and an ESC module. The ESC module sends a voltage signal (8-10 volts) to the ECM. When the sensor detects detonation, the module turns off the circuit to the ECM and the voltage at ECM terminal "B7" drops to zero. The ECM then retards EST as much as 20 degrees in one degree increments to reduce detonation. This happens fast and frequently enough that if looking at this signal with a DVM, you won't see zero volts, but an average voltage somewhat less than what is normal with no detonation.

A loss of the knock sensor signal or a loss of ground at the ESC module would cause the signal at the ECM to remain high. The ECM would control ignition timing (EST) as if no detonation were occurring. The EST would not be retarded, and detonation could become severe enough under heavy engine load conditions to result in pre-ignition and potential engine damage.

Loss of the ESC signal to the ECM for more than 2.2 seconds would cause the ECM to retard the EST to its maximum retard of 20 degrees from the spark table. If retarded continuously, this could result in sluggish performance and cause a Code 43 to set.

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

1. If the "Scan" tester "KNOCK SIGNAL" display is fluctuating widely, the ECM is monitoring a low voltage signal on circuit No. 457 at ECM terminal "B7".
2. Probing ESC harness terminal "C" with a test light connected to 12 volts should result in "OLD PA3" (knock signal) display holding a steady reading due to more than 8 volts having been applied to ECM terminal "B7" through circuit No. 457.
3. If greater than 6 volts is measured at ECM terminal "B7", circuit No. 457 is okay. The fault is due to a poor connection at the ECM or the ECM is faulty.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following

1. Poor connection Inspect ECM harness connectors for backed out terminal "B7", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittents If connections and harness checks out okay, use "Scan" tester to check ESC "KNOCK SIGNAL" while moving related connectors and wiring harness. If the failure is induced, the knock signal display will change. This may help to isolate the location of the malfunction.

Schematic, Code 43: Electronic Spark Control (ESC). Scheme 213

Flow Chart, Code 43: Electronic Spark Control (ESC). Scheme 214

Flow Chart, Code 43: Electronic Spark Control (ESC). Scheme 215

CODE 44 - LEAN EXHAUST INDICATION

The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". If measured with a 10-megohm digital voltmeter, this may read as low .32 volt. The oxygen (O2) sensor varies the voltage within a range of about one volt, if the exhaust is rich, down through about .10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is less than about 600°F (360°C). An open sensor circuit or cold sensor causes "open loop" operation. Code 44 is set when the O2 sensor signal voltage on circuit No. 412 remains less than .2 volt for 60 seconds or more and the system is operating in "closed loop".

Using the "Scan" tester, observe the block learn values at different RPM and airflow conditions. The "Scan" tester also displays the block cells, so the block learn values can be checked in each of the cells to determine when Code 44 may have been set. If the conditions for Code 44 exists the block learn values will be around 150. Check the following

1. Oxygen sensor pigtail may be mispositioned and contacting the exhaust manifold.
2. Check for intermittent ground in wire between connector and sensor.
3. A Mass Airflow (MAF) sensor output that causes the ECM to sense a lower than normal airflow will cause the system to go lean. Disconnect the MAF sensor and if the lean condition is gone, replace the MAF sensor.
4. Perform injector balance test, refer to CHART C2A - INJECTOR BALANCE TEST.
5. Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set Code 44.
6. System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various road speeds and/or loads to confirm problem. See fuel system diagnosis CHART A7 - FUEL PRESSURE TEST.
7. If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust across the oxygen sensor. Vacuum or crankcase leaks can cause a lean condition.
8. If all of the above checks are okay, replace oxygen sensor.

Flow Chart, Code 44: Lean Exhaust Indication. Scheme 216

Flow Chart, Code 44: Lean Exhaust Indication. Scheme 217

CODE 45 - RICH EXHAUST INDICATION

The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". If measured with a 10-megohm digital voltmeter, this may read as low as .32 volt. The oxygen sensor varies the voltage within a range of about one volt if the exhaust is rich, down through about .10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is less than about 600°F (360°C). An open sensor circuit or cold sensor causes "open loop" operation.

Code 45 is set when the oxygen sensor signal voltage or circuit No. 412 remains greater than .7 volt for 30 seconds and in "closed loop". Engine time after start is one minute or more and throttle angle is 3-45 percent.

Using the "Scan" tester, observe the block learn values at different RPM and airflow conditions. Some "Scan" testers also display the block cells, so the block learn values can be checked in each of the cells to determine when the Code 45 may have been set. If the conditions for Code 45 exists, block learn values will be around 115.

If an open occurs at circuit No. 453, HEI induced electrical "noise" may result, causing simulated reference pulses to be picked up by the ECM on the reference line of the 4-wire EST harness. The additional pulses result in a higher than actual engine speed signal. The ECM will increase injector pulse width ("on" time) to match the increased RPM signal. "Scan" tester will show higher than actual RPM, which can help in diagnosing this problem.

Check for fuel saturation. Charcoal canister may be full of liquid fuel. An output that causes the ECM to sense a higher than normal airflow can cause the system to go rich. Disconnecting the MAF sensor will allow the ECM to set a fixed value for the sensor. Substitute a different MAF sensor if the rich condition is gone while the sensor is disconnected or use MAF Sensor Tester (J 36101) and test MAF sensor.

System will go rich if pressure is too high. The ECM can compensate for some increase, however, if it gets too high, a Code 45 may be set. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

An intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.

An EGR staying open (especially at idle) will cause the oxygen sensor to indicate a rich exhaust, and this set a Code 45.

Flow Chart, Code 45: Rich Exhaust Indication. Scheme 218

Flow Chart, Code 45: Rich Exhaust Indication. Scheme 219

CODE 51 - PROM ERROR (FAULTY OR INCORRECT PROM)

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

Clear all codes and confirm "CLOSED LOOP" operation and no "SERVICE ENGINE SOON" light.

CODE 52 - CALPAK ERROR (FAULTY OR INCORRECT CALPAK)

Note. Check that all pins are fully inserted in the socket if okay, replace prom, clear memory and recheck. If CODE 52 reappears, replace ECM.

Clear all codes and confirm "CLOSED LOOP" operation and no "SERVICE ENGINE SOON" light.

CODE 55 ECM ERROR

Note. Replace electronic control module (ECM)

Clear all codes and confirm "CLOSED LOOP" operation and no "SERVICE ENGINE SOON" light.

PFI (ECM) Terminal ID (3.0L "N" Body). Scheme 220

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the car being tested may vary slightly from these due to battery or alternator charging level.

The following conditions must be met before testing

1. Engine at operating temperature.
2. Engine in closed loop operation.
3. Engine idling ("Engine Run" column).
4. Test terminal NOT grounded.
5. Scanner or ALDL tool NOT installed.

PFI ECM Terminal ID (3.8L "A", "C" & "H" Bodies). Scheme 221

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the car being tested my vary slightly from these due to battery or alternator charging level.

The following conditions must be met before testing

1. Engine at operating temperature.
2. Engine in closed loop operation.
3. Engine idling ("Engine Run" column).
4. Test terminal NOT grounded.
5. Scanner or ALDL tool NOT installed.

PFI ECM Terminal ID (3.8L Turbo "G" Body). Scheme 222

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the car being tested my vary slightly from these due to battery or alternator charging level.

The following conditions must be met before testing

1. Engine at operating temperature.
2. Engine in closed loop operation.
3. Engine idling ("Engine Run" column).
4. Test terminal NOT grounded.
5. Scanner or ALDL tool NOT installed.

Component Location (3.0L "N" Body & 3.8L Turbo "G" Body). Scheme 223

Component Location (3.8L Non-Turbo "A", "C" & "H" Bodies). Scheme 224

Port Fuel Injection Wiring Diagram (3.0L "N" Body). Scheme 225

Port Fuel Injection Wiring Diagram (3.8L "A" Body). Scheme 226

Port Fuel Injection Wiring Diagram (3.8L "C" & "H" Bodies). Scheme 227

Port Fuel Injection Wiring Diagram (3.8L Turbo "G" Body). Scheme 228

See also:
• 13
• 14
• 21
• 24
• 31
• 32
• 33
• 34
• 42
• 43
• 44
• 45
• 51
• 52
• 55