3.3l/3.8l Component Tests Buick Riviera VII

DIAGNOSIS & TESTING

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. Scanner or ALDL tool NOT installed.

MODEL IDENTIFICATION

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

The computerized engine control system monitors as many as 19 engine/vehicle functions. (Scheme 419) 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 419

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 the 3.3/3.8L PFI TESTS/CODES article in this section.
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 the TROUBLE SHOOTING procedures in the CCC TESTS W/O CODES article in this section. The comments there will send you to the proper component charts or tell you the most likely system/component to check.
5. After any repairs are made, clear any trouble codes and perform FIELD SERVICE MODE check again.

ALDL Connector Terminal Identification. Scheme 420

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 the 3.3/3.8L PFI TESTS/CODES article in this section.
7. 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.

THROTTLE BODY INJECTION

Scheme 421

Scheme 422

Scheme 423

ECM TERMINAL ID (3.3L VIN N, "A" BODY)

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

Scheme 424

Scheme 425

Scheme 426

Scheme 427

ECM TERMINAL ID (3.3L VIN N, "N" BODY)

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

Scheme 428

Scheme 429

Scheme 430

Scheme 431

ECM TERMINAL ID (3.3L VIN C, "C" & "H" BODIES)

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

Scheme 432

Scheme 433

Scheme 434

Scheme 435

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 check, no problems were found, a comparison of "Scan" tester parameters may be used to help locate intermittent and out-of-specification sensors. See SCAN TESTER - TEST DATA PARAMETERS table in this article.

If the "Scan" tester is not operating properly, check to verify it's operation 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 "M" and the ECM. Also check for an open diagnostic test terminal wire from ALDL terminal "B" to ECM. Use mini schematic from CHART A1 - NO "SERVICE ENGINE SOON" ("SES") LIGHT for terminal reference.

Diagnostic Circuit Check (Flow Chart). Scheme 436

Chart A1 Schematic, (3.3L "A" Body) No "SES" Light. Scheme 437

Chart A1 Schematic, (3.8L "C" & "H" Bodies) No "SES" Light. Scheme 438

Chart A1 Schematic, (3.3L "N" Body) No "SES" Light. Scheme 439

The "SERVICE ENGINE SOON" ("SES") light should be on steady when ignition is on and engine is off.

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

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

1. Engine Runs Okay: Check for faulty light bulb or open in circuit No. 419.
2. Engine Cranks, But Will Not Run: Check continuous battery power, check fuse or fusible link for open. Check for ECM ignition fuse open, ignition circuit No. 439 to ECM open or poor connection to ECM.

Flow Chart A1, No "Service Engine Soon" Light. Scheme 440

Chart A2 Schematic, (3.3L "A" Body) Won't Flash Code 12 "Service Engine Soon" Light On. Scheme 441

Chart A2 Schematic, (3.8L "C" & "H" Bodies) Won't Flash Code 12 "Service Engine Soon" Light On. Scheme 442

Chart A2 Schematic, (3.3L "N" Body) Won't Flash Code 12 "Service Engine Soon" Light On. Scheme 443

"SERVICE ENGINE SOON" light should be on steady when ignition is on and engine is off. 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 the light goes off when the ECM connector is disconnected, then circuit No. 419 is not shorted to ground.
2. 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. 461 is okay, the MEM-CAL or ECM may be at fault for the "NO ALDL" symptom.
3. This test will check for an open diagnostic circuit No. 451.
4. At this point, the "SERVICE ENGINE SOON" light wiring is okay. The problem is a faulty ECM or MEM-CAL. If Code 12 does not flash, the ECM should be replaced using the original MEM-CAL. Replace the MEM-CAL only after trying a new ECM, as a defective MEM-CAL is an unlikely cause of the problem.

Flow Chart A2, Won't Flash Code 12 "SES" Light On. Scheme 444

CHART A3 - ENGINE CRANKS BUT WON'T RUN

ALTERNATE WIRING COLORS "A" BODY CARS (1)

Chart A3 Schematic, (3.3L "A" Body) Cranks But Won't Run. Scheme 445

Chart A3 Schematic, (3.3L "N" Body) Cranks But Won't Run. Scheme 446

1. This test verifies that "SERVICE ENGINE SOON" (SES) light operation and TPS and coolant sensor signals are normal. A blinking injector test light verifies that the ECM is monitoring the ignition reference signal and attempting to activate the injectors. How bright the light blinks is not important. The "Scan" tester should indicate RPM while cranking.
2. This test will determine if the ignition module is not generating the reference pulses or if the wiring or ECM are at fault. Touching the test light to circuit No. 430 should cause RPM to display on "Scan" tester. This indicates the ECM and wiring are okay.
3. Because the Direct Ignition System (DIS) uses 2 plugs and wires to complete the circuit of each coil, the opposite spark plug wire should be left connected. If "RPM" was indicated during cranking, the ignition module is receiving a cranking signal, but "NO SPARK" at this test indicates the ignition module is not triggering the coil.
4. This test will determine if the ignition module is not triggering the problem coil or if the tested coil is at fault. This could also be performed by substituting a known good coil.
5. If test light is off, the 20-amp fuse could be blown or circuit No. 839 open or shorted to ground.

Flow Chart A3, Engine Cranks But Will Not Run (3.3L). Scheme 447

3.3L (2 OF 2)

1. This test simulates a reference pulse to the ECM. The ECM should cycle the injectors with each touch of terminal "C".
2. This check is to verify that the dual crank sensor has power and a ground which are both supplied by the C(3)I module.
3. This will test the ignition module's ability to process the simulated signal from the dual crank sensor.
4. This will check for a short to voltage on the injector circuits and for a faulty ECM.

Flow Chart A3, Engine Cranks But Will Not Run (3.3L). Scheme 448

While cranking, the ECM activates all 6 injector "driver" circuits simultaneously (all at one time). After a calibrated engine RPM is reached, and a good camshaft "synch" signal has been received by the ignition module, the ignition module sends a fuel control signal to the ECM and the injection mode of operation is changed to sequential (sprayed in spark plug firing order).

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

1. This test verifies "SERVICE ENGINE SOON" (SES) light operation 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. The crank signal has 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. By testing for spark on plug leads No. 1, 3 and 5, each ignition coil's ability to produce at least 25,000 volts is verified.
4. By testing the problem coil's control circuit with a test light, a determination can be made as to the problem coil being faulty or the module's internal driver for that coil being the source of the complaint.
5. Tests for battery voltage on circuit No. 1039. If voltage was present, the "light off" test result was caused by no activation pulse reaching the injector connector from the ECM.
6. Connecting the test light to 12 volts simulates a reference signal to the ECM which will result in an injector test light blink if circuit No. 430, the ECM and the injector "driver" circuits are all okay.
7. If the camshaft sensor signal circuit terminal "A" is momentarily jumped to the ground circuit terminal "C", and the engine is cranked without turning the ignition off, the response should be an injector test light blink. This is a result of the artificial synch signal being transmitted through the ignition module to ECM terminal "BD8" and the ECM activating the injector driver circuit.
8. Verifies a proper camshaft signal circuit voltage of 9-12 volts and a good ground from the ignition module to terminal "C" of the sensor connector.
9. This determines if reason for incorrect voltage reading was due to a fault in circuit No. 646, an open in circuit No. 645 or a faulty ignition module.
10. Jumping the camshaft sensor harness terminals "A" and "C" together simulates a synch signal to the ignition module. By jumping the crankshaft sensor harness terminals "B" and "C" together, a crankshaft signal is simulated which should cause the ECM to activate the fuel pump relay for 2 seconds.
11. This test verifies a proper crankshaft signal circuit voltage of 9-12 volts and a good ground from the ignition module to terminal "C" of the sensor connector.
12. Determines if reason for incorrect voltage reading was due to a fault in circuit No. 643, an open in circuit No. 645, or a faulty ignition module.

Chart A3 Schematic, Cranks But Won't Run (3.8L). Scheme 449

Flow Chart A3, Cranks But Won't Run (3.8L) (1 of 4). Scheme 450

Flow Chart A3, Cranks But Won't Run (3.8L) (2 of 4). Scheme 451

Flow Chart A3, Cranks But Won't Run (3.8L) (3 of 4). Scheme 452

Flow Chart A3, Cranks But Won't Run (3.8L) (4 of 4). Scheme 453

CHART A5 - FUEL SYSTEM ELECT. TEST (3.3L, "A" BODY)

Fuel pump relay will remain on as long as the engine is cranking or running, and the ECM is receiving ignition reference pulses. When the engine is stopped, the pump can be turned on by applying battery voltage to the test terminal. The fuel pump test terminal is located in the engine compartment. Improper fuel system pressure may contribute to a "engine cranks, but won't run" condition, Code 44 or 45, engine cut-out (may feel like ignition problems), hesitation, loss of power and poor fuel economy.

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

1. Check for battery voltage and ground at the fuel pump relay.
2. Check that the ECM is supplying voltage to the fuel pump relay.
3. This checks the fuel pump circuit to the tank for opens or shorts.

Chart A5 Schematic, Fuel System Elect. Test (3.3L "A" Body). Scheme 454

Flow Chart A5, Fuel System Electrical Test (3.3L "A" Body). Scheme 455

CHART A5 - FUEL SYSTEM ELECT. TEST

When the engine is stopped, the pump can be turned on by applying battery voltage to the test terminal. The fuel pump test terminal is located in the engine compartment. Improper fuel system pressure may contribute to a "engine cranks, but won't run" condition, Code 44 or 45, engine cut-out (may feel like ignition problems), hesitation, loss of power and poor fuel economy.

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

1. If the fuse is blown, a short to ground in circuits No. 120 or 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. 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. 839.
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.

Additional Checks

This step checks the oil pressure switch to be sure it provides ignition feed to the fuel pump should the pump relay fail. A failed 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 "engine cranks, but wont run".

Chart A5 Schematic, Fuel System Elect. Test (3.3L "N" Body). Scheme 456

Flow Chart A5, Fuel Sys. Elect. Test (3.3L "N" Body, 1 of 2). Scheme 457

Flow Chart A5, Fuel Sys. Elect. Test (3.3L "N" Body, 2 of 2). Scheme 458

CHART A5 - FUEL SYSTEM ELECTRICAL TEST

When the engine is stopped, the pump can be turned on by applying battery voltage to the test terminal. The fuel pump test terminal is located in the engine compartment. Improper fuel system pressure may contribute to a cranks, but won't run condition, Code 44 or 45, engine cut-out (may feel like ignition problems), hesitation, loss of power and poor fuel economy.

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

1. If the fuse is blown, a short to ground in circuits No. 120 or 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. 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. 839.
6. Checks for open in fuel pump circuits No. 120 or 150 or the pump.
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.

This step checks the oil pressure switch to be sure it provides ignition feed to the fuel pump should the pump relay fail. A failed 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 "engine cranks, but wont run".

Chart A5 Schematic, Fuel System Elect. Test (3.8L w/Standard Instrument Cluster). Scheme 459

Flow Chart A5 (1 of 2), Fuel Sys Elect Test (3.8L w/Standard Instrument Cluster). Scheme 460

Flow Chart A5 (2 of 2), Fuel Sys Elect Test (3.8L w/Standard Instrument Cluster). Scheme 461

When the engine is stopped, the pump can be turned on by applying battery voltage to the test terminal. The fuel pump test terminal is located in right front corner of engine compartment. Improper fuel system pressure may contribute to a "engine cranks, but won't run" condition, Code 44 or 45, engine cut-out (may feel like ignition problems), hesitation, loss of power and poor fuel economy.

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

1. If the fuse is blown, a short to ground in circuits No. 120 or 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. 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. 839.
6. Checks for open in fuel pump 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.

This step checks the oil pressure switch to be sure it provides ignition feed to the fuel pump should the pump relay fail. A failed 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 "engine cranks, but won't run".

Chart A5 Schematic, Fuel Sys Elect Test (3.8L Except w/Standard Instrument Cluster. Scheme 462

Flow Chart A5 (1 of 2), Fuel Sys Elect Test (3.8L Except w/Standard Instrument Cluster. Scheme 463

Flow Chart A5 (2 of 2), Fuel Sys Elect Test (3.8L Except w/Standard Instrument Cluster. Scheme 464

CHART A7 - FUEL PRESSURE TEST (3.3L "A" BODY)

Fuel pump can be turned on by applying battery voltage to the test terminal. The fuel pump test terminal is located in the engine compartment. Improper fuel system pressure may contribute to an "engine cranks, but won't run" condition, Code 44 or 45, cut-out (may feel like ignition problem), 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 34-44 psi (2.4-3.0 kg/cm 2 ). This pressure is controlled by spring pressure. Pressure should not leak down after fuel pump is shut off.
2. When the engine is idling, vacuum is high and is applied to fuel regulator diaphragm. This will overcome regulator spring pressure, resulting in a lower fuel pressure of 32-36 psi (2.2-2.5 kg/cm 2 ).
3. Applying 12-14 in. Hg vacuum to pressure regulator should result in a fuel pressure drop of at least 4-6 psi (.28-.42 kg/cm 2 ).
4. Pressure that leaks down may be caused by the in-tank fuel pump check valve not holding, the pump coupling hose leaking, the fuel pressure regulator valve leaking or an injector sticking open.

Chart A7, Fuel Pressure Test (3.3L "A" Body). Scheme 465

Flow Chart A7 (1 of 2), Fuel Pressure Test (3.3L "A" Body). Scheme 466

FUEL PRESSURE TEST (2 OF 3) (3.3L "A" BODY)

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

1. 5) If fuel system has pressure, but pressure is less than specification, condition may be caused by one of the following: Regulated Pressure, But Less Than Specification 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.
2. 6) Do not allow fuel pressure to increase to greater than regulated pressure. When battery voltage is applied to the pump test terminal, pressure should be greater than 47 psi (3.3 kg/cm 2 ).
3. 7) This test determines if the high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.

Flow Chart A7 (2 of 2), Fuel Pressure Test (3.3L "A" Body). Scheme 467

Installation

1. Remove fuel filler cap. Install gauge bleed hose into an appropriate container. Open valve and bleed fuel pressure from lines. Using Remover (J-37088-1), remove fuel lines. Use a shop towel and appropriate container to collect fuel from lines.
2. Install Adapters (J-37287) in engine and body side fuel lines. Leave valves open on adapters. Install fuel filler cap.
3. Install bleed hose and insert into an appropriate container. Bleed air from fuel lines by cycling ignition on several times. It is normal for pressure to drop slightly when pump stops.

Removal

1. Remove fuel filler cap. Install gauge bleed hose into an appropriate container. Open valve and bleed fuel pressure from lines. Remove fuel lines. Use a shop towel and appropriate container to collect fuel from lines. Install fuel lines. Install fuel filler cap.
2. Install bleed hose and insert into an appropriate container. Bleed air from fuel lines by cycling ignition on several times. It is normal for pressure to drop slightly when pump stops. Start engine and check for fuel leaks.

CHART A7 - FUEL PRESSURE TEST (3.3L "N" BODY)

Fuel pump can be turned on by applying battery voltage to the test terminal. The test terminal is located in the engine compartment. Improper fuel system pressure may contribute to an "engine cranks, but won't run" condition, Code 44 or 45, cut-out (may feel like ignition problem), 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 fuel pressure gauge tap to absorb fuel leakage that may occur when installing gauge. With ignition on, pump pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). This pressure is controlled by spring pressure. Pressure should not leak down after fuel pump is shut off.
2. When the engine is idling, vacuum is high and is applied to the fuel regulator diaphragm. This will overcome regulator spring pressure, resulting in a lower fuel pressure of 31-44 psi (2.2-3.1 kg/cm 2 ).
3. Applying 12-14 in. Hg vacuum to pressure regulator should result in a fuel pressure drop of at least 3-6 psi (.21-.42 kg/cm 2 ).
4. Pressure that leaks down may be caused by the in-tank fuel pump check valve not holding, the pump coupling hose leaking, the fuel pressure regulator valve leaking or an injector sticking open.
5. If fuel system has pressure, but pressure is less than specification, condition may be caused by one of the following: Regulated Pressure, But Less Than Specification 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. Do not allow fuel pressure to increase to greater than regulated pressure. When battery voltage is applied to the pump test terminal, pressure should be greater than 47 psi (3.3 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, Fuel Pressure Test (3.3L "N" Body). Scheme 468

Flow Chart A7 (1 of 2), Fuel Pressure Test (3.3L "N" Body). Scheme 469

Flow Chart A7 (2 of 2), Fuel Pressure Test (3.3L "N" Body). Scheme 470

CHART A7 - FUEL PRESSURE TEST (3.8L "C" & "H" BODIES)

Fuel pump can be turned on by applying battery voltage to the test terminal. The fuel pump test terminal is located in the engine compartment. Improper fuel system pressure may contribute to an "engine cranks, but won't run" condition, Code 44 or 45, cut-out (may feel like ignition problem), 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 40-47 psi (2.8-3.3 kg/cm 2 ). This pressure is controlled by spring pressure. 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 32-42 psi (2.2-3.0 kg/cm 2 ).
3. The application of 12-14 in. Hg vacuum to the pressure regulator should result in a fuel pressure drop of at least 5-8 psi (.35-.56 kg/cm 2 ).
4. Pressure that leaks down may be caused by the in-tank fuel pump check valve not holding, the pump coupling hose leaking, the fuel pressure regulator valve leaking or an injector sticking open.
5. If fuel system has pressure, but pressure is less than specification, condition may be caused by one of the following: Regulated Pressure, But Less Than Specification 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 deliver maximum pressure. When battery voltage is applied to the pump test terminal, pressure should be greater than 75 psi (5.3 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.

Flow Chart A7, Fuel Pressure Test (3.8L "C" & "H" Bodies). Scheme 471

Flow Chart A7, Fuel Pressure Test (3.8L "C" & "H" Bodies). Scheme 472

Flow Chart A7, Fuel Pressure Test (3.8L "C" & "H" Bodies). Scheme 473

CHART B1 - RESTRICTED EXHAUST SYSTEM CHECK

Before any components are replaced, exhaust system must be checked for restrictions. Check at O2 sensor procedure may be used to diagnose condition.

Flow Chart B1, Restricted Exhaust System Check. Scheme 474

CHECK AT O2 SENSOR

Remove O2 sensor. Install back pressure tester in place of O2 sensor as shown in illustration. After test is completed, ensure O2 sensor threads are coated with anti-seize compound before installing.

Diagnosis

1. Start engine and bring to operating temperature. Increase engine speed to 2500 RPM and note gauge. Reading should not exceed 1.25 psi (.09 kg/cm 2 ).
2. If specification is exceeded, exhaust system restriction is indicated. Check complete exhaust system for collapsed pipe, heat distress and possible internal muffler failure.
3. If none of the conditions in step 2) exist, check for restricted catalytic converter. Replace if necessary.

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 SYSTEM DIAGNOSIS 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.

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

1. With ignition off, connect Fuel Pressure Gauge (J-34730-1) to pressure tap. Unplug harness connector at all injectors. Connect Injector Tester (J-34730-3) to one of the injectors.
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.

Chart C2A, Injector Balance Test. Scheme 475

CHART C2B - IDLE AIR CONTROL (3.3L)

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. Turn ignition off and disconnect ECM. Turn the ignition on and probe terminals to check for this condition.

A slow unstable 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. For possible causes of an improper idle, check the following

1. System Too Lean - Idle speed may be too high or too low, or engine 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 volt, 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 C2B Schematic, Idle Air Control (3.3L). Scheme 476

Chart C2B Flow Chart, Idle Air Control (3.3L). Scheme 477

CHART C2B - IDLE AIR CONTROL (3.8L)

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. Turn ignition off and disconnect ECM. Turn ignition on and probe terminals to check for this condition.

A slow unstable 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. For possible causes of an improper idle, check the following

1. System Too Lean - Idle speed may be too high or too low, or engine 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 volt, 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 C2B Schematic, Idle Air Control (3.8L). Scheme 478

Chart C2B Flow Chart, Idle Air Control (3.8L). Scheme 479

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 ALDL "test" terminal is grounded with the engine stopped or if following conditions are met

1. Engine run time is more than 30-45 seconds.
2. Coolant temperature more than 158°F (70°C).
3. Vehicle is operating in "closed" loop

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.

Chart C3 Schematic, Canister Purge Check (3.3L "A" & "N" Bodies). Scheme 480

Chart C3 Schematic, Canister Purge Check (3.8L "C" & "H" Bodies). Scheme 481

Flow Chart C3, Canister Purge Check. Scheme 482

CHART C4H1 - C3I MISFIRE AT IDLE (3.3L)

1. If the misfire problem exists under load only, see CHART C4H2 - C3I MISFIRE UNDER LOAD (3.3L). Engine RPM should drop equally on all plug leads. If the spark is okay, refer to SYMPTOM testing in the appropriate CCC TESTS W/O CODES article in this section.
2. Spark Tester (ST-125) must be used because it is essential to verify adequate available secondary voltage (25,000 volts) at the spark plug.
3. If ignition coils are carbon tracked, the coil tower spark plug wire nipples may be damaged. By checking the secondary resistance, a coil with an open secondary may be located. A secondary coil resistance reading of 5000-13,000 ohms is acceptable.
4. By switching a normally operating coil into the position of the malfunctioning one, a determination can be made as to fault being the coil or ignition module.

Chart C4H1 Schematic, C3I Misfire At Idle (3.3L "A" Body). Scheme 483

Chart C4H1 Schematic, C3I Misfire At Idle (3.3L "N" Body). Scheme 484

Flow Chart C4H1, C3I Misfire At Idle (3.3L). Scheme 485

CHART C4H2 - C3I MISFIRE UNDER LOAD (3.3L)

1. If the misfire problem exists at idle only, see CHART C4H1 - C3I MISFIRE AT IDLE. If the spark is okay, refer to SYMPTOM testing in the appropriate CCC TESTS W/O CODES article in this section.
2. Spark Tester (ST-125) must be used because it is essential to verify adequate available secondary voltage (25,000 volts) at the spark plugs. Spark should jump the tester gap on all 6 leads. This simulates a "load" condition.
3. If ignition coils are carbon tracked, the coil tower spark plug wire nipples may be damaged. By checking the secondary resistance, a coil with an open secondary may be located. A secondary coil resistance reading of 5000-13,000 ohms is acceptable.
4. By switching a normal operating coil into the position of a malfunctioning one, a determination can be made if the coil or ignition module being at fault.

Chart C4H2 Schematic, C3I Misfire Under Load ("A" Body). Scheme 486

Chart C4H2 Schematic, C3I Misfire Under Load ("N" Body). Scheme 487

Flow Chart C4H2, C3I Misfire Under Load (3.3L). Scheme 488

CHART C4F1 - C3I MISFIRE AT IDLE (3.8L "C" & "H" BODIES)

1. If the misfire problem exists under load only, see CHART C4F2 - C3I MISFIRE UNDER LOAD (3.8L "C" & "H" BODIES). Engine RPM should drop equally on all plug leads. If no fault is found, refer to SYMPTOM testing in the appropriate CCC TESTS W/O CODES article in this section.
2. Spark Tester (ST-125) must be used because it is essential to verify adequate available secondary voltage (25,000 volts) at the spark plug. If spark is okay, refer to SYMPTOM testing in the appropriate CCC TESTS W/O CODES article in this section.
3. If 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 fault being the coil or ignition module.

Chart C4F1 Schematic, C3I Misfire At Idle (3.8L "C" & "H" Bodies). Scheme 489

Flow Chart C4F1, C3I Misfire At Idle (3.8L "C" & "H" Bodies). Scheme 490

CHART C4F2 - C3I MISFIRE UNDER LOAD (3.8L "C" & "H" BODIES)

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

1. If the misfire problem exists at idle only, see CHART C4F1 - C3I MISFIRE AT IDLE (3.8L). If no faults are found, refer to SYMPTOM testing in the appropriate CCC TESTS W/O CODES article in this section.
2. Spark Tester (ST-125) must be used because it is essential to verify adequate available secondary voltage (25,000 volts) at the spark plugs. Spark should jump the tester gap on all 6 leads. This simulates a "load" condition.
3. If ignition coils are carbon tracked, the coil tower spark plug wire nipples may be damaged.
4. By switching a normal operating coil into the position of a malfunctioning one, a determination can be made if the coil or ignition module being at fault.

Note. If fuel shut-off occurs under wide open throttle conditions, this may be due to vehicle reaching its fuel shutoff RPM. This is based upon RPM and axle ratio, and is an internal function of the MEM-CAL.

Chart C4F2 Schematic, C3I Wiring Diagram Misfire Under Load (3.8L "C" & "H" Bodies). Scheme 491

Flow Chart C4F2, C3I Misfire Under Load (3.8L "C" & "H" Bodies). Scheme 492

CHART C5 - ELECTRONIC SPARK CONTROL (ESC)

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

1. With engine idling, there should not be a knock signal present.
2. Tapping on the engine lift hook bracket should simulate a knock signal to determine if the sensor is capable of detecting detonation. If no knock is detected, knock on engine block closer to sensor.
3. If engine has an internal problem which is creating knock, sensor may be responding to this internal failure.
4. This step determines if the sensor is faulty or if the ESC portion of the MEM-CAL is faulty. Be sure MEM-CAL is properly installed.

While observing the knock signal on a "Scan" tester, there should be an indication that knock is present when detonation can be heard. Detonation is most likely to occur under high engine load conditions.

Chart C5 Schematic, Electronic Spark Control ("A" & "N" Bodies). Scheme 493

Chart C5 Schematic, Electronic Spark Control ("C" & "H" Bodies). Scheme 494

Flow Chart C5, Electronic Spark Control (ESC). Scheme 495

CHART C7 - EXHAUST GAS RECIRCULATION (3.8L)

The digital EGR valve is designed to accurately supply EGR to the engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through 3 orifices which increment in size to produce 7 combinations. When solenoid is energized, the armature with attached shaft and swivel pintle is lifted, opening the orifice. Flow accuracy is dependent on metering orifice size only, which results in improved control.

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

1. Disconnect 4-wire EGR connector. Install a fused jumper from battery to terminal "D" of the EGR valve. Start engine and allow to idle. Grounding terminal "A" should result in a small change in RPM, while terminal "C" should result in a large change in RPM. Engine may stall when terminal "C" is grounded. If the EGR valve shows signs of extreme heat (melting), check the exhaust system for blockage. See CHART B1 - RESTRICTED EXHAUST SYSTEM CHECK. If the exhaust system is plugged due to a restricted converter, this may be due to a defective injector or injector circuit which is causing injector to open constantly.

Chart C7 Schematic, Exhaust Gas Recirculation (3.8L). Scheme 496

Flow Chart C7, Exhaust Gas Recirculation (3.8L). Scheme 497

CHART C8 - TORQUE CONVERTER CLUTCH

The TCC will engage when the engine is warmed up, vehicle speed is greater than about 32 MPH, throttle sensor output is not changing (indicating a steady road speed), 3rd gear switch is closed and the brake switch is 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 25 MPH the 2nd gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding the ALDL "test" 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. Test light should turn on as circuit No. 422 is Grounded.

The "Scan" tester only indicates when the ECM has commanded the TCC driver to engage. This does not confirm that the TCC has engaged. To determine if the TCC has engaged, RPM should drop when the "Scan" tester indicates the TCC driver has turned on.

Each gear switch opens as the appropriate clutch is applied. All switches are open in 4th gear.

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

Chart C8 Schematic, TCC (3.3L "A" Body W/ 125-C Trans.). Scheme 498

Chart C8 Schematic, TCC (3.3L "N" Body W/ 125-C Trans.). Scheme 499

Flow Chart C8, TCC (3.3L W/ 125-C Transmission). Scheme 500

CHART C8B - TORQUE CONVERTER CLUTCH

1. Some "Scan" testers display the state of these switches in different ways. Be familiar with the type of tester being used. All switches should be in the closed state during this test, the tester should read the same for 2nd, 3rd and 4th gear switches.
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.

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.

Chart C8B Schematic, TCC (3.3L "A" Body W/ 440-T4 Trans.). Scheme 501

Flow Chart C8B (1 of 2, TCC (3.3L "A" Body W/ 440-T4 Trans.). Scheme 502

3.3L "A" BODY WITH 440-T4 TRANSMISSION (2 OF 2)

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. All switches should be in the closed state during this test, the tester should read the same for 2nd, 3rd and 4th gear switches.
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 switch should be grounded in this test, disconnecting TCC connector should cause "Scan" tester switch state to change.
4. Switch state should change when 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.

Chart C8B Schematic, TCC (3.3L "A" Body W/ 440-T4 Trans.). Scheme 503

Flow Chart C8B (2 of 2), TCC (3.3L "A" Body W/ 440-T4 Trans.). Scheme 504

CHART C8A - TORQUE CONVERTER CLUTCH

The TCC will engage when the engine is warmed up, vehicle speed is greater than 28 MPH, throttle position sensor output is not changing (indicating a steady road speed) and the brake switch is 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.
3. TCC electrical circuits have checked out properly. Fault may be an internal hydraulic problem.

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, TCC (3.8L W/ 440-T4 Trans.). Scheme 505

Flow Chart C8A, TCC (3.8L W/ 440-T4 Transmission). Scheme 506

TCC - 3.8L WITH 440-T4 TRANSMISSION (2 OF 2)

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. All switches should be in the closed state during this test, the tester should read the same for 2nd, 3rd and 4th gear switches.
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 2nd, 3rd and 4th 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.

Chart C8A Schematic, TCC (3.8L W/ 440-T4 Transmission). Scheme 507

Flow Chart C8A, TCC (3.8L W/ 440-T4 Transmission). Scheme 508

CHART C10 - A/C CLUTCH CONTROL

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement .3 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 (WOT) 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. This test checks operation of A/C cycling switch.
2. This test checks to see if the ECM is controlling the A/C clutch control relay.
3. This test checks for open circuit on either side of relay coil.

Chart C10, Schematic, A/C Clutch Control (3.3L "A" Body). Scheme 509

Flow Chart C10, A/C Clutch Control (3.3L "A" Body). Scheme 510

3.3L "A" BODY (2 OF 2)

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 or ground.
3. Checks for open in circuit No. 67 to relay.
4. Checks to see that A/C "on" signal is getting to ECM circuit No. 67. A test light off at the time indicates circuit No. 67 is open between the cycling switch and the ECM.

Chart C10 Schematic, A/C Clutch Control (3.3L "A" Body). Scheme 511

Flow Chart C10, A/C Clutch Control (3.3L "A" Body). Scheme 512

CHART C10 - A/C CLUTCH CONTROL (3.3L "N" BODY)

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement .3 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 (WOT) operation, hot engine restarts, high power steering pressure conditions, when engine speeds are greater than 6000 RPM and during IAC reset. The A/C clutch will remain disengaged when Code 66 is present or there is no A/C request seen by the ECM.

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

1. The ECM will only energize the A/C relay when the engine is running. This will determine if the relay of circuit No. 459 is faulty.
2. Determines if the signal is reaching the ECM through circuits No. 50 and 66. Signal should only be present when the A/C or defrost mode is selected.
3. A short to ground in any part of the A/C request circuit could be the cause of the blown fuse.
4. If the ECM is receiving a high power steering pressure signal, the ECM will disengage the A/C clutch.
5. With the engine idling and the A/C on, the ECM should be grounding circuit No. 459, causing the test light to be on.

Chart C10, Schematic, A/C Clutch Control (3.3L "N" Body). Scheme 513

Flow Chart C10, A/C Clutch Control (3.3L "N" Body). Scheme 514

CHART C10A - A/C CLUTCH CONTROL

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 (WOT) 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 operation of A/C cycling switch.
2. Checks to see if the ECM is controlling the A/C clutch control relay.
3. Checks for open circuit on either side of relay coil.

Chart C10A, Schematic, A/C Clutch Control (3.8L "C" & "H" Bodies). Scheme 515

Flow Chart C10A, A/C Clutch Control (3.8L "C" & "H" Bodies). Scheme 516

3.8L "C" & "H" BODIES (2 OF 2)

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

1. Checks 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 to relay.
4. Verifies 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 Schematic, A/C Clutch Control (3.8L "C" & "H" Bodies). Scheme 517

Flow Chart C10A, A/C Clutch Control (3.8L "C" & "H" Bodies). Scheme 518

CHART C12A - COOLING FAN FUNCTIONAL CHECK (3.3L "A" BODY)

The ECM energizes the cooling fan relays (pusher fan optional) if the coolant temperature is greater than specification. Fans may run for up to 10 minutes.

1. 150 Watt Fan Relay - Energizes when coolant temperature reaches 208°F (98°C).
2. Pusher Fan Relay - Energizes when coolant temperature reaches 226°F (108°C) or refrigerant pressure exceeds 245 psi (17.23 kg/cm 2 ).

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

1. Grounding the ALDL "test" terminal by-passes all timers and turns on the cooling fan drivers.
2. Fan should be on when A/C is requested at idle.
3. If ECM connector is okay, the driver inside the ECM is faulty and the ECM must be replaced.

Chart C12A, Schematic, Cooling Fan Function Check (3.3L "A" Body). Scheme 519

Flow Chart C12A, Cooling Fan Function Check (3.3L "A" Body). Scheme 520

CHART C12B - NO COOLING FAN(S) (3.3L "A" BODY)

The ECM energizes the cooling fan relays (pusher fan optional) if the coolant temperature is greater than specification. Fans may run for up to 10 minutes.

1. 150 Watt Fan Relay - Energizes when coolant temperature reaches 208°F (98°C).
2. Pusher Fan Relay - Energizes when coolant temperature reaches 226°F (108°C) or refrigerant pressure exceeds 245 psi (17.23 kg/cm 2 ).

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

1. Test light should be on because the "F" and "D" terminals are fed directly from the ignition.
2. Test light should be on as grounding the ALDL "test" terminal will turn on the ECM driver, allowing current to flow.
3. Jumping terminal "A" to "E" feeds the fan motor directly and it should turn on.
4. Test light should be on as "A" terminals are connected directly to battery voltage.

Chart C12B, Schematic, No Cooling Fan(s) (3.3L "A" Body). Scheme 521

Flow Chart C12B, No Cooling Fan(s) (3.3L "A" Body). Scheme 522

CHART C12C - COOLING FAN(S) ALWAYS ON (3.3L "A" BODY)

The ECM energizes the cooling fan relays (pusher fan optional) if the coolant temperature is greater than specification. Fans may run for up to 10 minutes.

1. 150 Watt Fan Relay - Energizes when coolant temperature reaches 208°F (98°C) or refrigerant pressure exceeds 150 psi (10.55 kg/cm 2 ).
2. Pusher Fan Relay - Energizes when coolant temperature reaches 226°F (108°C) or refrigerant pressure exceeds 245 psi (17.23 kg/cm 2 ).

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

1. Removing the relay interrupts current flow to the fan motor so the fan(s) should not be on.
2. Test light should be off as the driver should be off when A/C is not requested and coolant temperature is less than 208°F (98°C).
3. Test light should be off as the A/C system should not have high pressure due to the A/C not being requested.
4. If the test light goes off when Black "CD" connector is disconnected, the ECM driver is faulty and the ECM must be replaced.

Chart C12C, Schematic, Cooling Fan(s) Always On (3.3L "A" Body). Scheme 523

Flow Chart C12C, Cooling Fan(s) Always On (3.3L "A" Body). Scheme 524

CHART C12A - COOLING FAN FUNCTIONAL CHECK (3.3L "N" BODY)

ECM will energize cooling fan when Code 14 or 15 is set, A/C pressure is high or coolant temperature is greater than 212°F (100°C).

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

1. Fan should be on when ALDL "test" terminal is grounded.
2. Fan should be running if the A/C compressor is running.

If the vehicle has an overheat problem, it must be determined if the problem is due to an actual boilover, a faulty coolant temperature warning light or a defective temperature gauge. If the gauge or light indicates overheating and no boilover is detected, the gauge circuit should be checked. If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not turning on, the coolant sensor may have shifted calibration and should be checked.

Chart C12A, Schematic, Cooling Fan Function Check (3.3L "N" Body). Scheme 525

Flow Chart C12A, Cooling Fan Function Check (3.3L "N" Body). Scheme 526

CHART C12B - NO COOLING FAN (3.3L "N" BODY)

ECM will energize cooling fan when Code 14 or 15 is set, A/C pressure is high or coolant temperature is greater than 212°F (100°C).

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

1. Test light should be on as the ignition switch is turned on.
2. Test light should be on as grounding the ALDL "test" terminal turns on the ECM driver.
3. Test light should be on as terminal is direct from battery voltage.

If the vehicle has an overheat problem, it must be determined if the problem is due to an actual boilover, a faulty coolant temperature warning light or a defective temperature gauge. If the gauge or light indicates overheating and no boilover is detected, the gauge circuit should be checked. If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not turning on, the coolant sensor may have shifted calibration and should be checked.

Chart C12B, Schematic, No Cooling Fan (3.3L "N" Body). Scheme 527

Flow Chart C12B, No Cooling Fan (3.3L "N" Body). Scheme 528

CHART C12C - COOLING FAN ALWAYS ON (3.3L "N" BODY)

ECM will energize cooling fan when Code 14 or 15 is set, A/C pressure is high and vehicle speed is less than 30 MPH, or coolant temperature is greater than 212°F (100°C).

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

1. The cooling fan runs continuously if Codes 14, 15 and/or 66 are present.
2. If test light is on, circuit No. 535 has to be grounded or the ECM driver is faulty.

If the vehicle has an overheat problem, it must be determined if the problem is due to an actual boilover, a faulty coolant temperature warning light or a defective temperature gauge. If the gauge or light indicates overheating and no boilover is detected, the gauge circuit should be checked. If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not turning on, the coolant sensor may have shifted calibration and should be checked.

Chart C12C, Schematic, Cooling Fan Always On (3.3L "N" Body). Scheme 529

Flow Chart C12C, Cooling Fan Always On (3.3L "N" Body). Scheme 530

CHART C12A - COOLING FAN FUNCTIONAL CHECK (3.8L)

The cooling fan is energized through a low speed, high speed and optional heavy duty cooling fan relay.

1. Low Speed Relay - The low speed relay is energized by the ECM when the coolant temperature reaches 214°F (101°C). The low speed relay will also function anytime the A/C is requested.
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.

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

1. Grounding the ALDL "test" terminal should cause the ECM to ground circuit No. 536 and the fan to run at high speed.
2. By ungrounding the "test" terminal, and disconnecting the coolant temperature sensor connector, the ECM will think the coolant temperature is -38°F (-39°C) and cause a rich fuel mixture. Coolant fan should run at low speed.
3. When jumping the coolant temperature sensor wires together, "Scan" tester should show temperature of about 304°F (151°C). High speed fan should be on when key is cycled from off to on.
4. Jumping the A/C pressure switch harness will cause the cooling fan(s) to run at high speed.
5. This step will see if the ECM monitors the coolant sensor temperature properly. Anytime the coolant temperature exceeds 214°F (101°C) and vehicle speed is less than 35 MPH, ECM will turn on the low speed cooling fan. If engine temperature continues to climb, the high speed fan will come on.

Chart C12A, Schematic, Cooling Fan Functional Check (3.8L). Scheme 531

Flow Chart C12A, Cooling Fan Functional Check (3.8L). Scheme 532

CHART C12B - COOLING FAN ALWAYS ON (3.8L)

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, ensure that circuit No. 535 is not shorted to battery voltage. If not shorted to voltage, the ECM is shorted internally.
4. If the test light is off after disconnecting, ensure that circuit No. 536 is not shorted to battery voltage. If not shorted to voltage, the ECM is shorted internally.

Chart C12B, Schematic, Cooling Fan Always On (3.8L). Scheme 533

Flow Chart C12B, Cooling Fan Always On (3.8L). Scheme 534

CHART C12C - NO LOW SPEED COOLING FAN (3.8L)

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

1. Checks for battery voltage at relay harness connector.
2. Jumping terminal No. 1 to No. 4 by-passes the relay which should cause the fan to run if fan motor and wiring to the motor are good.
3. Grounding the ALDL "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, motor connection or motor.

Chart C12C, Schematic, No Low Speed Cooling Fan (3.8L). Scheme 535

Flow Chart C12C, No Low Speed Cooling Fan (3.8L). Scheme 536

CHART C12D - NO HIGH SPEED COOLING FAN (3.8L)

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

1. Test light should be on because harness terminal No. 2 has battery voltage with ignition on.
2. Jumpering terminal No. 1 to No. 4 by-passes the relay which should cause the fan to run if fan motor and wiring to the motor are good.
3. Checks circuit No. 536 back to ECM. If circuit is okay, relay is faulty.
4. Checks wiring to cooling fan motor. If okay, problem is connection, motor or motor ground.

Chart C12D, Schematic, No High Speed Cooling Fan (3.8L). Scheme 537

Flow Chart C12D, No High Speed Cooling Fan (3.8L). Scheme 538

PFI Wiring Diagram (3.3L VIN N, "A" Body). Scheme 539

PFI Wiring Diagram (3.3L VIN N, "N" Body). Scheme 540

PFI Wiring Diagram (3.8L VIN C, "C" & "H" Bodies). Scheme 541