3.3l/3.8l Pfi Tests W/codes Buick Skylark VI

MODEL/BODY 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

BASIC DIAGNOSTIC PROCEDURE

Note. Most 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»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes) 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 «STANDARDIZED ECM TROUBLE CODE DEFINITION»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes) table in this article.
3. If no trouble codes were displayed, proceed to «FIELD SERVICE MODE CHECK»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes__field-service-mode-check) for fuel injected systems.
4. If no trouble is indicated by FIELD SERVICE MODE check and/or a driveability problem exists, refer to SYMPTOM DIAGNOSIS and/or «SCAN TESTER USAGE»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes__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 the «FIELD SERVICE MODE»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes__field-service-mode-check) check.

Scheme 3

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. For exact location of ALDL, see appropriate figure under «COMPONENT LOCATION»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes) in this article. Insert jumper wire across terminal "B" (diagnostic "test" terminal), and terminal "A" (ground). (Scheme 3) CAUTION: Inserting spade lug (jumper lead) into terminals of ALDL connector grounds ALDL "test" terminal. Do not ground ALDL connector until after ignition is on (engine not running).
2. "SERVICE ENGINE SOON" light should flash Code 12. Code 12 consists of "FLASH", pause, "FLASH", "FLASH" followed by a longer pause. 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 digital voltmeter.

If "Scan" tester is not available, it is possible to read flashes of the "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 Code 21. The first series of flashes are the first digit of trouble code. The 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 "test" 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.

STANDARDIZED ECM TROUBLE CODE DEFINITIONS

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

TROUBLE CODE DETERMINATION (HARD OR INTERMITTENT)

During any diagnostic procedure, it must be determined if codes are "hard" failure codes or "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. See CLEARING TROUBLE CODES in this article.
2. Apply parking brake and place transmission in Neutral or Park. Block drive wheels and start engine. "SERVICE ENGINE SOON" light should go out. Run warm engine at specified curb idle for 2 minutes and note "SERVICE ENGINE SOON" light.
3. If "SERVICE ENGINE SOON" light comes on, MANUALLY 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.
6. Charts where a stored trouble code leads you to a particular problem. See «STANDARDIZED ECM TROUBLE CODE DEFINITION»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes) and DIAGNOSTIC AIDS in this article.
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.

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

The "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.

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, test light, ohmmeter, digital voltmeter with 10-megohm impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights 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.

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. 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.

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.

"NON-SCAN" VERSION

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.

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 4

"SCAN" VERSION

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/CODES article in this section.

"Scan" Diagnostic Circuit Check. Scheme 5

CHART A1: NO "SERVICE ENGINE SOON" (SES) LIGHT

"SERVICE ENGINE SOON" 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" ("SES") 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.

Diagnostic Aids - Engine Runs Okay

Check for faulty light bulb or open in circuit No. 419. 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.

Chart A1: No "SES" Light Ckt Diag (3.3L A Body). Scheme 6

Chart A1: No "SES" Light Ckt Diag (3.3L N Body). Scheme 7

Chart A1: No "SES" Light Ckt Diag (3.8L C/H Body). Scheme 8

Chart A1: No "Service Engine Soon" Light Flow Chart. Scheme 9

CHART A2: WON'T FLASH CODE 12, "SES" LIGHT ON

"SERVICE ENGINE SOON" (SES) 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 MEMCAL or ECM may be at fault for the "NO ALDL" symptom.
3. Checks 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 MEMCAL. If Code 12 does not flash, the ECM should be replaced using the original MEMCAL. Replace the MEMCAL only after trying a new ECM, as a defective MEMCAL is an unlikely cause of the problem.

Chart A2: No Code 12, "SES" Light On Ckt Diag (3.3L N Body). Scheme 10

Chart A2: No Code 12, "SES" Light On Ckt Diag (3.8L C/H Body). Scheme 11

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

CHART A3: ENGINE CRANKS BUT WON'T RUN (3.3L)

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.

ALTERNATE WIRING COLORS "A" & "N" BODY CARS (1)

Chart A3: Cranks But Won't Run Ckt Diag (3.3L A Body). Scheme 13

Chart A3: Cranks But Won't Run Ckt Diag (3.3L N Body). Scheme 14

Chart A3: Cranks But Won't Run Flow Chart (3.3L) (1 of 2). Scheme 15

CHART A3: ENGINE CRANKS BUT WON'T RUN (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.

Chart A3: Cranks But Won't Run Flow Chart (3.3L) (2 of 2). Scheme 16

CHART A3: ENGINE CRANKS BUT WON'T RUN (1 OF 4) (3.8L)

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.

Chart A3: Cranks But Won't Run Ckt Diag (3.8L). Scheme 17

Chart A3: Cranks But Won't Run Flow Chart (3.8L) (1 of 4). Scheme 18

CHART A3: ENGINE CRANKS BUT WON'T RUN (2 OF 4) (3.8L)

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

1. 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.

Chart A3: Cranks But Won't Run Flow Chart (3.8L) (2 of 4). Scheme 19

CHART A3: ENGINE CRANKS BUT WON'T RUN (3 OF 4) (3.8L)

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

1. 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.
2. 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.
3. 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.
4. 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.

Chart A3: Cranks But Won't Run Flow Chart (3.8L) (3 of 4). Scheme 20

CHART A3: ENGINE CRANKS BUT WON'T RUN (4 OF 4) (3.8L)

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

1. 10) Jumping the crankshaft 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.
2. 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.
3. 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: Cranks But Won't Run Flow Chart (3.8L) (4 of 4). Scheme 21

CHART A5: FUEL SYSTEM ELECTRICAL 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 cutout (may feel like ignition problems), hesitation, loss of power and poor fuel economy.

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

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

Chart A5: Fuel System Elect. Ckt Diag (3.3L A Body). Scheme 22

Chart A5: Fuel System Elect Test Flow Chart (3.3L A Body). Scheme 23

CHART A5: FUEL SYSTEM ELECTRICAL TEST (1 OF 2) (3.3L N BODY)

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 cutout (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.

Chart A5: Fuel System Elect. Ckt Diag (3.3L N Body). Scheme 24

Chart A5: Fuel System Elect. Test Flow Chart (1 of 2) (3.3L N Body). Scheme 25

CHART A5: FUEL SYSTEM ELECTRICAL TEST (2 OF 2) (3.3L N BODY)

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

1. 6) Checks for open in relay ground circuit No. 450.
2. 7) Determines if the ECM is in control of the fuel pump relay through circuit No. 465.
3. 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 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: Fuel System Elect. Test Flow Chart (2 of 2) (3.3L N Body). Scheme 26

CHART A5: FUEL SYSTEM ELECT TEST (1 OF 2, 3.8L W/STD CLUSTER)

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 cutout (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.

Chart A5: Fuel System Elect. Ckt Diag (3.8L W/Std Cluster). Scheme 27

CHART A5: FUEL SYSTEM ELECT TEST (2 OF 2, 3.8L W/STD CLUSTER)

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

1. 6) Checks for open in fuel pump circuits No. 120 or 150 or the pump.
2. 7) Determines if the ECM is in control of the fuel pump relay through circuit No. 465.
3. 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: FUEL SYS ELECT TEST (1 OF 2, 3.8L W/O STD CLUSTER)

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 cutout (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.

Chart A5: Fuel System Elect. Ckt Diag (3.8L W/O Std Cluster). Scheme 28

Chart A5: Fuel System Elect Flow Chart (1 of 2) (3.8L W/O Std Cluster). Scheme 29

CHART A5: FUEL SYS ELECT TEST (2 OF 2, 3.8L W/O STD CLUSTER)

1. 6) Checks for open in fuel pump relay ground circuit No. 450.
2. 7) Determines if the ECM is in control of the fuel pump relay through circuit No. 465.
3. 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 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 A7: FUEL PRESSURE TEST (1 OF 3) (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, cutout (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 intank 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 Ckt Diag (3.3L A Body). Scheme 30

Chart A7: Fuel Pressure Test Flow Chart (1 of 3) (3.3L A Body). Scheme 31

CHART A7: 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.

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.

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, cutout (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 intank 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 N Body). Scheme 32

Chart A7: Fuel Pressure Test Flow Chart (1 of 2) (3.3L N Body). Scheme 33

CHART A7: FUEL PRESSURE TEST (2 OF 2) (3.3L N 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.

Chart A7: Fuel Pressure Test Flow Chart (2 of 2) (3.3L N Body). Scheme 34

CHART A7: FUEL PRESSURE TEST (1 OF 2) (3.8L C/H 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, cutout (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 intank 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 Ckt Diag (3.8L C/H Body). Scheme 35

Chart A7: Fuel Pressure Test Flow Chart (1 of 2) (3.8L C/H Body). Scheme 36

CHART A7: FUEL PRESSURE TEST (2 OF 2) (3.8L C/H 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) 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 ).
3. 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 Flow Chart (2 of 2) (3.8L C/H Body). Scheme 37

CODE 13: OPEN O2 SENSOR CIRCUIT

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. At least 40 seconds 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 30 seconds. If all the above conditions for a Code 13 exist, system will not go into "closed loop".
2. Determines if the sensor or the wiring is the cause of the 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, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

If connections and harness check 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.

Code 13: Open O2 Sensor Ckt Diag (3.3L A/N Body). Scheme 38

Code 13: Open O2 Sensor Ckt Diag (3.3L C/H Body). Scheme 39

Code 13: Open O2 Sensor Circuit Flow Chart. Scheme 40

CODE 14: CTS SIGNAL VOLTAGE LOW

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 284°F (140°C) for a 10 seconds or more.
2. This test will determine if circuit No. 410 is shorted to ground, which will cause the conditions for Code 14. If Code 14 is set, the ECM uses a default coolant value of about 120°F (49°C); however, the "Scan" tester will read the actual temperature indicated by the sensor.

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,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 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.

Code 14: CTS Signal Volt Lo Ckt Diag (3.3L A/N Body). Scheme 41

Code 14: CTS Signal Volt Lo Ckt Diag (3.8L C/H Body). Scheme 42

Code 14: CTS Signal Volt Lo Flow Chart. Scheme 43

CODE 15: CTS SIGNAL VOLTAGE HIGH

At operating temperature, voltage will measure about 1-2 volts at 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 -36°F (-38°C) for at least .4 second, with engine running.
2. This test simulates a Code 14. If the ECM recognizes the low signal voltage, (high temperature) and the "Scan" tester reads "140°C", the ECM and wiring are okay.
3. This test will determine if circuit No. 410 is open. Using a digital volt/ohmmeter, there should be 5 volts present at sensor connector. If Code 15 is set, the ECM uses a default coolant value of about 120°F (49°C); however, the "Scan" tester will read the actual temperature indicated by the sensor.

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, 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 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 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.

Code 15: CTS Signal Volt Hi Flow Chart. Scheme 44

CODE 16: SYSTEM VOLTAGE HIGH

The ECM monitors battery voltage on circuit No. 440. If the ECM detects battery voltage greater than 16 volts for more than 10 seconds, it will set a Code 16 in memory.

Note. Test numbers refer to test numbers on diagnostic chart. Charging battery with a charger and starting engine may set Code 16.

1. Test alternator output to determine proper operation of voltage regulator. Increase engine speed to a moderate level and measure voltage across battery terminals. If reading is greater than 16 volts, service alternator.

Check for poor connections or damaged harness. Also, check for an intermittent condition by starting engine and wiggling connection while monitoring battery voltage on the "Scan" tester. If voltage status changes abruptly, or if the engine stalls, check for loose connections.

Code 16: System Volt Hi Ckt Diag (3.3L A Body). Scheme 45

Code 16: System Volt Hi Ckt Diag (3.3L N Body). Scheme 46

Code 16: System Volt Hi (3.8L C/H Body). Scheme 47

Code 16: System Volt Hi Flow Chart. Scheme 48

CODE 21: TPS SIGNAL VOLTAGE HIGH

1. Code 21 will set if engine is running and the following conditions occur: TAPS signal voltage is greater than 4.9 volts at any time. TPS signal voltage is greater than 2.5 volts. Code 34 not present. Both conditions must be met for 5 seconds. With closed throttle, ignition on or engine at idle, voltage should be less than .38-.42 volt (3.3L) or .33-.46 volt (3.8L). If voltage is not okay, check TPS adjustment.
2. With the TPS sensor disconnected, Code 22 should set and 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, 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, 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.

Code 21: TPS Signal Volt Hi Flow Chart. Scheme 49

CODE 22: TPS SIGNAL VOLTAGE LOW

1. Code 22 will set if engine is running and TPS signal voltage is less than .24 volt (3.3L) or .1 volt (3.8L) for 4 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 .38-.42 volt (3.3L) or .33-.46 volt (3.8L). If voltage is not okay, check TPS adjustment.
4. Simulates a high signal voltage. Checks circuit No. 417 for an open condition.

The "Scan" tester reads throttle position in volts. Voltage should increase at a steady rate as throttle is moved from idle to 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, 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, 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.

Code 22: TPS Signal Volt Lo Flow Chart. Scheme 50

CODE 23: MAT SENSOR SIGNAL VOLTAGE HIGH (3.8L)

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, inspect air cleaner for presence of ice. If okay, replace the sensor. See INTERMITTENTS in the CCC TESTS W/O CODES article in this section.

Code 23: MAT Sensor Signal Volt Hi Flow Chart (3.8L). Scheme 51

CODE 24: VEHICLE SPEED SENSOR (VSS)

The Vehicle Speed Sensor (VSS) is a PM generator type located in the transmission or transaxle. As the vehicle moves, the generator creates AC voltage signal which is routed to the buffer inside the ECM. In the buffer, the AC 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.

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

1. Code 24 will set if vehicle speed equals less than 3 MPH when the following conditions occur: Engine is running. Vehicle is in high gear. No Code 29 or 31 is present. All conditions met for 40 seconds.
2. Before replacing ECM, check MEMCAL for proper application.

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

Inspect ECM harness connectors 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 at greater 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.

Code 24: VSS Ckt Diag. Scheme 52

Code 24: VSS Flow Chart. Scheme 53

CODE 25: MAT SENSOR SIGNAL VOLTAGE LOW (3.8L)

Code 25 will set if the following conditions occur

1. Signal voltage indicates manifold air temperature is greater than 275°F (135°C).
2. Vehicle speed is greater than 35 MPH.
3. Both of the above requirements are met for at least 16 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 185 ohms, replace sensor. See INTERMITTENTS in the CCC TESTS W/O CODES article in this section.

Code 25: MAT Sensor Signal Volt Lo Flow Chart (3.8L). Scheme 54

CODE 26: TCC QUAD-DRIVER CKT (3.3L W/125-C TRANS)

Each ECM Quad-Driver has a fault line which is monitored by the ECM. The ECM compares voltage values of the fault line with acceptable values in ECM memory. If the ECM senses other than accepted values, a Code 26 will set.

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

1. Light off confirms that the transmission 2nd gear apply switch is open.
2. At 25 MPH, the transmission 2nd gear apply switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding the ALDL "test" terminal should energize the TCC solenoid. This test checks the ECM's ability to supply a ground to the solenoid. The test light connected from 12 volts to ALDL terminal "F" will turn on as the circuit is grounded.

Check for poor connections at ECM. Check for misrouted harness. If wires are routed too close to high voltage wires (such as spark plug wires), electrical interference could occur. Inspect harness for damage caused by chafing. Also, check for cut or pinched wiring. If no faults can be found, problem may be due to transmission internal hydraulic fault.

Code 26: TCC Quad-Driver Ckt Diag (3.3L A Body W/125-C Trans). Scheme 55

Code 26: TCC Quad-Driver Ckt Diag (3.3L N Body W/125-C Trans). Scheme 56

Code 26: Flow Chart, TCC Quad-Driver Ckt (3.3L W/125-C Trans). Scheme 57

CODE 26: TCC QUAD-DRIVER CKT (3.3L A BODY W/440-T4 TRANS)

Each ECM Quad-Driver has a fault line which is monitored by the ECM. The ECM compares voltage values of the fault line with acceptable values in ECM memory. If the ECM senses other than accepted values, a Code 26 will set.

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

1. Checks fuse, brake switch and battery voltage circuit to the TCC solenoid.
2. Check for battery voltage on circuit No. 420.
3. Electrical circuits have checked out okay. If there is still a TCC engagement problem, may be due to transmission internal hydraulic fault.

Check for poor connections at ECM. Check for misrouted harness. If wires are routed too close to high voltage wires (such as spark plug wires), electrical interference could occur. Inspect harness for damage caused by chafing. Also, check for cut or pinched wiring.

Code 26: TCC Quad-Driver Ckt Diag (3.3L A Body W/440-T4 Trans). Scheme 58

Code 26: TCC Quad-Driver Ckt Diag (3.3L A Body W/440-T4 Trans). Scheme 59

CODE 26: QUAD-DRIVER CIRCUIT (1 OF 3) (3.8L)

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

1. The ECM does not know which driver caused the fault line to read incorrectly so each circuit must be tested. This tests the "SERVICE ENGINE SOON" light driver and circuit.
2. Quad-Driver symptoms are as follows: TCC, inoperative, Code 39. EGR, inoperative, Codes 63, 64 and 65. Hot light, on all the time, off during bulb check. Coolant fan, on low all the time or won't come on at all. Canister purge, poor driveability, rich.

Code 26: Quad-Driver Ckt Diag (3.8L). Scheme 60

Code 26: Quad-Driver Circuit Flow Chart (1 of 3) (3.8L). Scheme 61

CODE 26: QUAD-DRIVER CIRCUIT (2 OF 3) (3.8L)

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

1. 3) Test will determine which circuit is out of specification. All circuits except the hot light and "SERVICE ENGINE SOON" light should have battery voltage with the key on and engine off. The ALDL "test" terminal should not be grounded.

Monitor the voltage of each terminal while moving related harness connectors. If the failure is induced, the voltage reading will change. If code reappears for no apparent reason, replace ECM.

Code 26: Quad-Driver Circuit Flow Chart (2 of 3) (3.8L). Scheme 62

CODE 26: QUAD-DRIVER CIRCUIT (3 OF 3) (3.8L)

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

1. 4) This test will determine if the problem is the circuit or the component. As the factory installed ECM is protected with an internal fuse, it is highly unlikely that the ECM needs to be replaced.

Code 26: Quad-Driver Circuit Flow Chart (3 of 3) (3.8L). Scheme 63

CODE 27 OR 28: GEAR SWITCH CKTS (3.3L W/125-C TRANS)

The gear switches are located inside the transaxle. Switches are normally closed. As road speed increases, hydraulic pressure applies the specific gear clutches and the gear switch opens. The ECM uses the gear switches to control fuel delivery and TCC operation.

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

1. A digital volt/ohmmeter must be used in this test. A test light will not work due to the low voltage being supplied by the ECM.
2. Checks to see if the circuit is grounded through the switch.
3. Checks for a good, properly operating switch and checks circuit within transaxle for an improper ground.

Check for poor connections at ECM pins. Inspect harness for incorrect routing (too close to high voltage wiring) or chafing. Monitor the voltage of each terminal while moving related harness connectors. If the failure is induced, the voltage reading will change.

Code 27 or 28: Gear Switch Ckts Diag (3.3L A Body W/125-C Trans). Scheme 64

Code 27 or 28: Gear Switch Ckts Diag (3.3L N Body W/125-C Trans). Scheme 65

Code 27 or 28: Gear Switch Ckts Flow Chart (3.3L W/125-C Transmission). Scheme 66

CODE 28 OR 29: GEAR SWITCH CKTS (3.3L W/440-T4 TRANS)

The gear switches are located inside the transaxle. Switches are normally closed. As road speed increases, hydraulic pressure applies the specific gear clutches and the gear switch opens. The ECM uses the gear switches to control fuel delivery and TCC operation. Code 28 will set if circuit No. 108 indicates ground or closed switch for 10 seconds when the vehicle is in 4th gear or if circuit No. 108 indicates an open when engine is first started.

Code 29 will set if circuit No. 446 indicates ground or closed switch for 10 seconds when the vehicle is in 4th gear or if circuit No. 446 indicates an open when engine is first started.

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

1. A digital volt/ohmmeter must be used in this test. A test light will not work due to the low voltage being supplied by the ECM.
2. Checks to see if the circuit is grounded through the switch.
3. Checks for a good, properly operating switch and checks circuit within transaxle for an improper ground.

Check for poor connections at ECM pins. Inspect harness for incorrect routing (too close to high voltage wiring) or chafing. Monitor the voltage of each terminal while moving related harness connectors. If the failure is induced, the voltage reading will change.

Code 28 or 29: Gear Switch Ckts Diag (3.3L W/440-T4 Trans). Scheme 67

CODE 27/28 OR 29: GEAR SWITCH CIRCUITS (3.8L)

The gear switches are located inside the transaxle. Switches are normally closed. As road speed increases, hydraulic pressure applies the specific gear clutches and the gear switch opens. The ECM uses the gear switches to control fuel delivery and TCC operation.

Code 27 will set if no Code 29 is present, circuit No. 581 indicates ground or closed switch for 10 seconds when vehicle is in 4th gear, circuit No 581 indicates an open when the engine is first started or if circuit No. 446 is open when the engine is first started.

Code 28 will set if circuit No. 108 indicates ground or closed switch for 10 seconds when the vehicle is in 4th gear, circuit No. 108 indicates an open when engine is first started or circuit No. 446 is open when the engine is first started.

Code 29 will set if circuit No. 446 indicates ground or closed switch for 10 seconds when the vehicle is in 4th gear (TCC locked and brake not applied) or if circuit No. 446 indicates an open when engine is first started.

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

1. A digital volt/ohmmeter must be used in this test. A test light will not work due to the low voltage being supplied by the ECM.
2. Checks that the circuit is grounded through the switch.
3. Checks for a good, properly operating switch and checks circuit within transaxle for an improper ground.

Check for poor connections at ECM pins. Inspect harness for incorrect routing (too close to high voltage wiring) or chafing. Monitor the voltage of each terminal while moving related harness connectors. If the failure is induced, the voltage reading will change.

Code 27/28 or 29: Gear Switch Ckt Diag (3.8L). Scheme 68

Code 27/28 or 29: Gear Switch Ckts Flow Chart (3.8L). Scheme 69

CODE 31: PARK/NEUTRAL SWITCH CIRCUIT

The park/neutral switch contacts are part of the neutral start switch and are closed to ground in Park or Neutral and open in Drive. Code 31 will set if circuit No. 434 indicates an open for 4 consecutive starts or if conditions occur as follows

1. No Code 38 exists.
2. Circuit No. 434 indicates ground.
3. Transmission is in high gear.
4. TCC is locked on 4-speed only.
5. Vehicle speed is greater than 45 MPH and TPS is less than 15 percent (.94 volt) on 3-speed only.
6. All above conditions have been met for 12 seconds.

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

1. This test checks for a closed switch to ground in Park.
2. This test checks for an open switch in Drive.
3. Be sure "Scan" tester indicates Drive, even when wiggling shifter.

Code 31: Park/Neutral Switch Ckt Diag (3.3L A/N Body). Scheme 70

Code 31: Park/Neutral Switch Ckt Diag (3.8L C/H Body). Scheme 71

Code 31: Park/Neutral Switch Ckt Flow Chart. Scheme 72

CODE 34: MASS AIRFLOW (MAF) SENSOR

Code 34 is set when engine is running with no MAF sensor signal for greater than 4 seconds.

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

1. This step checks to see if ECM recognizes a problem.
2. A voltage reading at sensor harness terminal "A" of less than 4 or greater than 6 volts indicates a fault in circuit No. 492 or poor connections.
3. Verifies that both ignition voltage and a good ground are available.

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

1. Poor Connections - Inspect ECM pin "YF10" (3.3L) or "YD10" (3.8L) 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. Intermittent - 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.

Code 34: MAF Sensor Ckt Diag (3.3L A/N Body). Scheme 73

Code 34: MAF Sensor Ckt Diag (3.8L C/H Body). Scheme 74

Code 34: Mass Airflow Sensor Flow Chart. Scheme 75

CODE 38: BRAKE SWITCH CIRCUIT (3.3L)

Code 38 will set if no Code 24 is present, status at circuit No. 420 has not changed from high to low and vehicle speed has been greater than 35 MPH and back to zero MPH, 22 or more times.

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

1. Jumping the brake switch will determine if the ECM and wiring for the brake switch are okay.
2. Verifies the voltage to the brake switch.
3. Tests the brake switch for proper operation or misadjustment.

A Code 38 in conjunction with a Code 39 would mean a problem with one or more of the following components.

1. Fuse, circuit No. 639 ("A" Body) or 439 ("N" Body), brake switch wire before the splice.
2. OR: A single Code 38 is the result of a wire or circuit No. 420 problem between the splice and the ECM, poor connection to the ECM, or possibly the ECM.

Code 38: Brake Switch Ckt Diag (3.3L A Body). Scheme 76

Code 38: Brake Switch Ckt Diag (3.3L N Body). Scheme 77

Code 38: Brake Switch Circuit Flow Chart (3.3L). Scheme 78

CODE 38: BRAKE SWITCH CIRCUIT (3.8L)

Code 38 will set if no Code 24 is present, status at circuit No. 420 has not changed from high to low and vehicle speed has been greater than 35 MPH and back to zero MPH, 22 or more times.

A Code 38 in conjunction with a Code 39 would mean a problem with one or more of the following components.

1. Fuse, circuit No. 639, brake switch or wire before the splice.
2. A single Code 38 is the result of a wire or circuit No. 420 problem between the splice and the ECM, poor connection to the ECM, or possibly the ECM.

Code 38: Brake Switch Ckt Diag (3.8L). Scheme 79

Code 38: Brake Switch Circuit Flow Chart (3.8L). Scheme 80

CODE 39: TCC CIRCUIT (3.3L W/125-C TRANS)

Code 39 will set when no Code 28 is set, brake is not applied, TCC is commanded by ECM, transmission is in high gear, engine speed/vehicle speed ratio does not indicate that TCC has engaged and all of the mentioned conditions have been met for greater than 15 seconds.

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

1. Checks for voltage source and ECM commanded ground.
2. Checks for an open or faulty brake input switch.
3. Checks for TCC engagement.
4. Checks the ECM for proper operation.

A poor connection can cause an intermittent Code 39. Using a digital voltmeter connected to the circuit, move the related wiring and connectors. An intermittent condition would cause a change in voltmeter status.

Code 39: TCC Ckt Flow Chart (3.3L W/125-C Trans). Scheme 81

CODE 39: TCC CIRCUIT (3.3L/3.8L W/440-T4 TRANS)

Code 39 will set when no Code 29 is set, brake is not applied, TCC is commanded by ECM, transmission is in high gear, engine speed/vehicle speed ratio does not indicate that TCC has engaged, and all of the mentioned conditions have been met for greater than 15 seconds (3.3L) or 30 seconds (3.8L).

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

1. Checks fuse, brake switch and battery power circuit to the TCC solenoid.
2. Checks availability of battery voltage at circuit No. 420.
3. Electrical circuits have checked out okay. If there is a TCC engagement problem still, problem is possibly caused by a transmission internal hydraulic failure.

A Code 39 in conjunction with a Code 38 would mean a problem with one or more of the following components.

1. Fuse, circuit No. 639, brake switch or wire before the splice.
2. A single Code 39 is the result of a wire or circuit No. 420 problem between the splice and the ECM, circuit No. 422 problem between TCC solenoid and ECM, poor connection to the ECM, or possibly the ECM.

Code 39: TCC Ckt Diag (3.8L W/440-T4 Trans). Scheme 82

Code 39: TCC Ckt Flow Chart. Scheme 83

CODE 41, CAM SENSOR CIRCUIT ("C" & "H" BODIES; 3.8L)

Quick reference

1. (Scheme 85)for Code 41 flow chart.
2. (Scheme 84)for Code 41 supplemental wiring.

All Updated Information

All the Code 41 information here (including the flow chart) has been updated as per the General Motors Technical Service Bulletins (TSBs) listed below. All outdated information has been discarded.

1. Buick 91-6E-14
2. Oldsmobile 91-T-45
3. Pontiac 91-6-18

Circuit Description

The 3800 engine uses the simultaneous mode of fuel injection during start-up. As the engine speed attains the 400 RPM level and a cam signal has been received by the ECM from C3I module, the fuel injection switches modes to sequential injection.

This is accomplished by use of a cam interrupter magnet and a cam sensor "Hall Effect" switch. The cam sensor sends a signal (sync-pulse) to the ignition module when cylinder #1 is 25° after top dead center on the compression stroke. This signal is used to start sequential fuel injection with the proper cylinder.

If cam signal is lost to the ECM, the fuel delivery will switch back to the simultaneous mode of injection. THE ENGINE WILL CONTINUE TO RUN. IT WILL RESTART AFTER SHUT DOWN.

Code 41 is set when the following conditions are met

1. Engine is running.
2. Cam sensor signal not received by the ECM in last 2 seconds.

Test Description

The numbers below refer to the circled numbers in the diagnostic flow chart.

1. This step verifies proper operation of circuits 633, 644, and 645. (Scheme 84)for circuit identification.
2. Step validates the integrity of Circuit 630 from the ignition module to the ECM. (Scheme 85)for circuit identification.
3. If the camshaft gear magnet is interfacing with the cam sensor the voltage reading will be zero, bumping engine will cause the condition to go away.
4. If the voltage reading of terminal "BC5" is constantly varying and connection to terminal "BC5" are good, 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 or Damaged Harness: Inspect ECM harness connectors for backed out terminal "BC5", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test: If connections and harness check okay, monitor a digital voltmeter connected from ECM terminal "BC5" to ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change. This may help to isolate the location of the malfunction.

Note. For Supplemental Wiring Schematic below the letter "B" on PCM connector terminal designates black connector.

Scheme 84

Scheme 85

CODE E041, CAM SENSOR CIRCUIT ("E" BODIES; 3.8L)

Quick reference

1. see scheme 102for Code E041 flow chart.
2. (Scheme 86)for Code E041 supplemental wiring.

All the Code E041 information here (including the flow chart) has been updated as per the General Motors Technical Service Bulletins (TSBs) listed below. All outdated information has been discarded.

1. Buick 90-8-22
2. Oldsmobile 91-T-45

During cranking, the ignition module monitors the dual crank sensor sync signal. The sync signal is used to determine the correct cylinder pair to spark first.

After the sync signal has been processed by the ignition module, it sends a fuel control reference pulse to the ECM. When the ECM receives this pulse it will command all six injectors to open for one priming shot of fuel in all cylinders.

After the priming, the injectors are left off for the next six fuel control reference pulses from the ignition module (two crankshaft revolutions). This allows each cylinder a chance to use the fuel from the priming shot.

During this waiting period, a cam pulse will have been received by the ECM. Now the ECM begins to operate the injectors sequentially based on true camshaft position.

However, if the cam signal is not present at start-up, a Code E041 will set and the ECM will start sequential fuel delivery in random pattern with a 1 in 6 chance that fuel delivery is correct.

The numbers below refer to the circled numbers in the diagnostic flow chart.

1. This step verifies proper operation of circuits 633, 644, and 645. (Scheme 84)for circuit identification.
2. Step validates the integrity of Circuit 630 from the ignition module to the ECM. (Scheme 85)for circuit identification.
3. If the camshaft gear magnet is interfacing with the cam sensor the voltage reading will be zero, bumping engine will cause the condition to go away.
4. If the voltage reading of terminal "BC5" is constantly varying and connection to terminal "BC5" are good, 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 or Damaged Harness: Inspect ECM harness connectors for backed out terminal "BC5", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test: If connections and harness check okay, monitor a digital voltmeter connected from ECM terminal "BC5" 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.

Scheme 86

CODE 42: EST IGNITION CIRCUIT

To set a Code 42 the following conditions must occur

1. Engine speed greater than 600 RPM with no EST pulse for 100 -200 milliseconds (open or grounded circuit No. 423).
2. OR: ECM commanding bypass 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 "BC7", either circuit No. 423 is shorted to ground, or the ignition module is faulty.
4. Checks to see if ignition module switches when the bypass circuit is energized by 12 volts through the test light. If the ignition module actually switches, the ohmmeter reading should shift to greater than 6000 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, 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, 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.

Code 42: EST Ignition Circuit Flow Chart. Scheme 87

CODE 43: ELECTRONIC SPARK CONTROL (ESC)

The ECM supples a 5-volt reference on the knock sensor signal line. Internal sensor circuitry will cause this voltage to pull down to about 2.5 volts PC. The knock sensor produces an AC voltage signal when knock occurs. This AC voltage signal will ride on the PC signal back to the ECM. Code 43 will set if voltage on circuit No. 496 is greater than 3.5 volts or less than 1.5 volts and this condition is met for 20 seconds.

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

1. If a Code 43 is detected, the ECM will retard spark timing by 10 degrees. If an audible knock is heard from the engine, repair the internal engine problem. Normally, no knock should be heard at idle.
2. If taping on the engine lift hook does not produce a knock signal, try tapping on the engine closer to the sensor before proceeding.
3. The ECM has a 5-volt pull up resistor which places a 5-volt reference on the knock sensor signal line.
4. This test determines if the knock sensor is faulty or if the ESC portion of the MEMCAL is faulty.

Check circuit No. 496 for a potential open or short to ground. Also, check for proper installation of the MEMCAL.

Code 43: ESC Ckt Diag (3.3L A/N Body). Scheme 88

Code 43: ESC Ckt Diag (3.8L C/H Body). Scheme 89

Code 43: Electronic Spark Control (ESC) Flow Chart. Scheme 90

CODE 44: LEAN EXHAUST INDICATION

Code 44 is set when the oxygen sensor signal voltage on circuit No. 412 remains less than .25 volt for up to 4.5 minutes and the system is operating in "closed loop".

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

1. Running the engine at 1200 RPM will keep the O2 sensor hot so an accurate display of voltage is maintained. Opening the sensor wire should result in a voltage display of .35-.55 volt. If the display is still fixed at less than .35 volt, the fault is a short to ground in circuit No. 412 or a faulty ECM.

Using the "Scan" tester, observe block learn values at different RPM and airflow conditions. "Scan" tester also displays block cells, so the block learn values can be checked in each cell to determine when Code 44 may have been set. If the conditions for Code 44 exist, 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 below in this article.
5. Water, even in small amounts, near the intank 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.

Code 44: Lean Exhaust Indication Ckt Diag (3.8L C/H Body). Scheme 91

Code 44: Lean Exhaust Indication Flow Chart. Scheme 92

CODE 45: RICH EXHAUST INDICATOR

Code 45 is set if no Code 21 or 22 is set and the O2 sensor signal voltage or circuit No. 412 remains greater than .75 volt for 2 minutes in "closed loop", engine time after start is one minute or more and TPS voltage is .52-1.1 volts (3.3L) or .7-1.4 volts (3.8L).

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

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 a leaking or sticking injector.

Check for fuel saturation. Charcoal canister may be full of liquid fuel.

Check MAF sensor. 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.

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.

Code 45: Rich Exhaust Indicator Flow Chart. Scheme 93

CODE 46: POWER STEERING PRESSURE SWITCH (3.3L)

The Power Steering Pressure Switch (PSPS) is normally open. Turning the steering wheel will increase pressure and close the switch, pulling voltage on the switch circuit low. Code 46 will set when power steering circuit voltage is low (indicating high pressure) and vehicle speed is greater than 40 MPH. Both of these conditions must be met for more than 25 seconds.

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

1. Different makes of "Scan" tester will display this information differently. Refer to the manufacturer's operating manual for additional information.
2. Checks to determine if circuit No. 901 ("A" Body) or 495 ("N" Body) is shorted to ground.
3. This should simulate a closed switch.

Note. Circuit No. 495 on "N" body.

Code 46: Power Steering Pressure Switch Ckt Diag (3.3L). Scheme 94

Code 46: Power Steering Pressure Switch Flow Chart (3.3L). Scheme 95

CODE 46: POWER STEERING PRESSURE SWITCH (3.8L)

The power steering pressure switch is normally open. Turning the steering wheel will increase pressure and close the switch, pulling voltage on the switch circuit low. Code 46 will set when power steering circuit voltage is low (indicating high pressure) and vehicle speed is greater than 40 MPH. Both of these conditions must be met for more than 25 seconds.

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

1. Different makes of "Scan" tester will display this information differently. Refer to the manufacturer's operating manual for additional information.
2. This step determines if the fault is in the switch or circuit.
3. If the display switches when circuit No. 495 is grounded, the fault is an open circuit No. 450.

Check harness and for poor connections at ECM and switch. If connections and harness check out okay, monitor switch status on a "Scan" tester while wiggling harness and connectors. An abrupt change in status would indicate a problem.

Code 46: Power Steering Pressure Switch Ckt Diag (3.8L). Scheme 96

Code 46: Power Steering Pressure Switch Flow Chart (3.8L). Scheme 97

CODE 48: MISFIRE DIAGNOSIS

Note. If multiple codes are present, go to the lowest code first. Repairing Code 13, 44 or 45 may correct Code 48. 3.3L - Code 48 will set on 3.3L if the TPS is .58-.93 volt, RPM is 1500-2500, MPH is 50-60, O2 cross counts are greater than 32 (125-C transmission) or 26 (440-T4 transmission) and if all of these conditions are met for 30 seconds. 3.8L - Code 48 will set on 3.8L if the TPS is .48-1.30 volts, RPM is 1300-2100, MPH is 50-60, O2 cross counts are greater than 21 and if all of these conditions are met for 30 seconds.

1. Ignition System Checks - Remove each spark plug and inspect. If plug(s) are fouled, check ignition wires, ignition coil and ignition module operation (see appropriate CHART C4). If plugs are cracked or worn, replace plugs. If no fault is found, perform basic engine checks.
2. Fuel System Checks - Check for restricted fuel system (injectors, fuel pump,lines and filter). Perform injector balance test. Verify proper injector circuit operation using Injector Tester (J-34730-3 ). See «CHART C2A: INJECTOR BALANCE TEST»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes__chart-c2a-injector-balance-test) . Check fuel pump pressure and volume.
3. Basic Engine Checks - Perform engine compression check. Unless spark plug condition or compression check identifies a specific cylinder, road test vehicle under test conditions to reverify Code 48 prior to engine disassembly. Upon disassembly, inspect pistons, rings, valves, valve springs and valve guides. Check for worn or damaged camshaft lobes or lifters.

Code 48: Misfire Diagnosis Flow Chart. Scheme 98

CODE 51: MEMCAL ERROR

Check that all pins are fully inserted in ECM socket. If okay, replace MEMCAL. Clear memory and recheck for Code 51. If code reappears, replace ECM.

CODE 63/64 OR 65: EGR FLOW CHECK (3.8L)

On closed throttle coast down, the ECM will cycle the integral EGR solenoids on and off individually and look for a resulting change in engine RPM and O2 sensor activity.

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

1. If a code is set, inspect EGR for damage. Disconnect the 4-wire connector at the EGR valve. Install a fused jumper from battery voltage to terminal "D" of the EGR valve. Start engine. Using a jumper wire, ground terminals "A", "B" and "C" one at a time. A noticeable change in engine RPM should be noted as each terminal is grounded. Grounding terminal "A" should result in a small change, while terminal "C" should result in a large change, or even cause engine to stall.

Note. If EGR valve shows signs of excessive heat (melting), check the exhaust system for blockage. See CHART B1 RESTRICTED EXHAUST SYSTEM CHECK. Repair as necessary. If exhaust system has been damaged, check for an injector which may be constantly injecting fuel. Repair as necessary and check oil for fuel contamination.

An intermittent code may be caused by poor connections at ECM or EGR valve, or possible damage to harness. Also, to help locate intermittent in the harness, connect a digital voltmeter to the suspected circuit. Wiggle the harness and related wiring while monitoring voltage. If the reading changes abruptly, the intermittent has been induced.

Code 63/64 or 65: EGR Flow Check Ckt Diag (3.8L). Scheme 99

Code 63/64 or 65: EGR Flow Check Flow Chart (3.8L). Scheme 100

CODE 66: A/C PRESSURE SENSOR CKT (3.3L N BODY)

The A/C pressure sensor is a variable resistor which sends a signal to the ECM relative to A/C system pressure. This information is used by the ECM to determine A/C load on the engine. Low pressure will cause a low return signal voltage of about .5 volt. High pressure will cause a high return signal voltage of about 4.5 volts. Code 66 will set if the voltage signal falls outside of this range for 25 seconds.

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

1. This step checks the voltage signal that is being received by the ECM.
2. Checks to see if the high voltage signal is from a shorted sensor or a short to voltage in the circuit. Normally, disconnecting the sensor would make the circuit go to near zero volts.
3. Checks to see if the low voltage signal is from the sensor or the circuit. Jumping the sensor signal to 5 volts checks the circuit, connections and ECM.
4. This step checks to see if the low voltage signal was due to an open in the sensor or circuit, or the 5-volt reference circuit since the prior step eliminated the pressure switch.

Code 66 sets when signal voltage falls outside of the expected range. This code is not caused by an A/C refrigerant problem. If problem is intermittent, check for opens or shorts in the harness or for poor connections. If okay, replace the A/C pressure sensor. If Code 66 reappears, replace the ECM.

Code 66: A/C Pressure Sensor Ckt Diag (3.3L N Body). Scheme 101

Code 66: A/C Pressure Sensor Flow Chart (3.3L N Body). Scheme 102

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.

Check at O2 Sensor

Remove O2 sensor. Install back pressure tester in place of O2 sensor. (Scheme 103) After test is completed, ensure that O2 sensor threads are coated with anti seize compound before installation.

Installing Backpressure Tester. Scheme 103

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 104

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: Idle Air Control Ckt Diag (3.3L). Scheme 105

Chart C2B: Idle Air Control Flow Chart (3.3L). Scheme 106

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: Idle Air Control Ckt Diag (3.8L). Scheme 107

Chart C2B: Idle Air Control Flow Chart (3.8L). Scheme 108

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: Canister Purge Check Ckt Diag (3.3L A/N Body). Scheme 109

Chart C3: Canister Purge Check Ckt Diag (3.8L C/H Body). Scheme 110

Chart C3: Canister Purge Check Flow Chart. Scheme 111

CHART C4H-1: C3I MISFIRE AT IDLE (3.3L)

1. If the misfire problem exists under load only, see «CHART C4H-2: C3I MISFIRE UNDER LOAD (3.3L)»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes__chart-c4h-2-c3i-misfire-under-load) . 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 C4H-1: C3I Misfire At Idle Flow Chart (3.3L). Scheme 112

CHART C4H-2: C3I MISFIRE UNDER LOAD (3.3L)

1. If the misfire problem exists at idle only, see «CHART C4H-1: C3I MISFIRE AT IDLE»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes__chart-c4h-1-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 C4H-2: C3I Misfire Under Load Flow Chart (3.3L). Scheme 113

CHART C4F-1: C3I MISFIRE AT IDLE (3.8L C/H BODY)

1. If the misfire problem exists under load only, see «CHART C4F-2: C3I MISFIRE UNDER LOAD (3»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes__chart-c4f-2-c3i-misfire-under-load) .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 C4F-1: C3I Misfire At Idle Flow Chart (3.8L C/H Body). Scheme 114

CHART C4F-2: C3I MISFIRE UNDER LOAD (3.8L C/H BODY)

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

1. If the misfire problem exists at idle only, see «CHART C4F-1: C3I MISFIRE AT IDLE (3»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes__chart-c4f-1-c3i-misfire-at-idle) .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 C4F-2: C3I Misfire Under Load Flow Chart (3.8L C/H Body). Scheme 115

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: Electronic Spark Control (ESC) Flow Chart. Scheme 116

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»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#33l38l-pfi-tests-wcodes__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: EGR Flow Chart (3.8L). Scheme 117

CHART C8: TCC (125-C TRANS, 3.3L A/N BODY)

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: TCC W/125-C Trans Flow Chart. Scheme 118

CHART C8B: TCC W/440-T4 TRANS (1 OF 2) (3.3L A BODY)

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: TCC W/440-T4 Trans Flow Chart (1 of 2) (3.3L A Body). Scheme 119

CHART C8B: TCC W/440-T4 TRANS (2 OF 2) (3.3L A BODY)

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: TCC W/440-T4 Trans Flow Chart (2 of 2) (3.3L A Body ). Scheme 120

CHART C8A: TCC W/440-T4 TRANS (1 OF 2) (3.8L)

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: TCC W/440-T4 Trans Ckt Diag (3.8L ). Scheme 121

Chart C8A: TCC W/440-T4 Trans Flow Chart (1 of 2) (3.8L ). Scheme 122

CHART C8A: TCC W/440-T4 TRANS (2 OF 2) (3.8L)

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: TCC W/440-T4 Trans Flow Chart (2 of 2)(3.8L ). Scheme 123

CHART C10: A/C CLUTCH CONTROL (1 OF 2) (3.3L A 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. 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: A/C Clutch Control Ckt Diag (3.3L A Body). Scheme 124

Chart C10: A/C Clutch Control Flow Chart (1 OF 2 3.3L A Body). Scheme 125

CHART C10: A/C CLUTCH CONTROL (2 OF 2) (3.3L A BODY)

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: A/C Clutch Control Flow Chart (2 0F 2 3.3L A Body). Scheme 126

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: A/C Clutch Control Flow Chart (3.3L N Body). Scheme 127

CHART C10A: A/C CLUTCH CONTROL (1 OF 2) (3.8L C/H 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 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: A/C Clutch Control Ckt Diag (3.8L C/H Body). Scheme 128

Chart C10A: A/C Clutch Control Flow Chart (1 of 2) (3.8L C/H Body). Scheme 129

CHART C10A: A/C CLUTCH CONTROL (2 OF 2) (3.8L C/H BODY)

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: A/C Clutch Control Flow Chart (2 of 2) (3.8L C/H Body). Scheme 130

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: Cooling Fan Function Check Ckt Diag (3.3L A Body). Scheme 131

Chart C12A: Cooling Fan Function Check Flow Chart (3.3L A Body). Scheme 132

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: No Cooling Fan(s) Flow Chart (3.3L A Body). Scheme 133

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: Cooling Fan(s) Always On Flow Chart (3.3L A Body). Scheme 134

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: Cooling Fan Function Check Ckt Diag (3.3L N Body). Scheme 135

Chart C12A: Cooling Fan Function Check Flow Chart (3.3L N Body). Scheme 136

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: No Cooling Fan Flow Chart (3.3L N Body). Scheme 137

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: Cooling Fan Always On Flow Chart (3.3L N Body). Scheme 138

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: Cooling Fan Functional Check Ckt Diag (3.8L). Scheme 139

Chart C12A: Cooling Fan Functional Check Flow Chart (3.8L). Scheme 140

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: Cooling Fan Always On Flow Chart (3.8L). Scheme 141

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: No Low Speed Cooling Fan Flow Chart (3.8L). Scheme 142

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: No High Speed Cooling Fan Flow Chart (3.8L). Scheme 143

Scheme 144

Scheme 145

Scheme 146

TERMINAL ID & VOLTAGE CHARTS (3.3L VIN N, A BODY)

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the vehicle 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. ALDL "test" terminal NOT grounded.
5. Scanner or ALDL tool NOT installed.

Scheme 147

Scheme 148

Scheme 149

Scheme 150

TERMINAL ID & VOLTAGE CHARTS (3.3L VIN N, N BODY)

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the vehicle 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. ALDL "test" terminal NOT grounded.
5. Scanner or ALDL tool NOT installed.

Scheme 151

Scheme 152

Scheme 153

Scheme 154

TERMINAL ID & VOLTAGE CHARTS (3.8L VIN C, C/H BODY)

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the vehicle 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. ALDL "test" terminal NOT grounded.
5. Scanner or ALDL tool NOT installed.

Scheme 155

Scheme 156

Scheme 157

Scheme 158

Wiring Diagram (3.3L VIN N, "A" Body). Scheme 159

Wiring Diagram (3.3L VIN N, "N" Body). Scheme 160

Wiring Diagram (3.8L VIN C, "C" & "H" Bodies). Scheme 161

See also:
• DIAGNOSTIC CIRCUIT CHECK
• FIELD SERVICE MODE CHECK
• SCAN TESTER USAGE
• CHART C2A: INJECTOR BALANCE TEST
• CHART B1
• CHART C4H-2: C3I MISFIRE UNDER LOAD (3.3L)
• CHART C4H-1: C3I MISFIRE AT IDLE
• CHART C4F-2: C3I MISFIRE UNDER LOAD (3
• CHART C4F-1: C3I MISFIRE AT IDLE (3