Tests W/codes - 3.8l "3800" (VIN C) Buick LeSabre VI

DIAGNOSTIC CIRCUIT CHECK

The diagnostic circuit check is an organized approach for identifying a problem caused by an electronic control system malfunction. If after completing diagnostic circuit check, no problems were found, a comparison of "Scan" tester parameters may be used to help locate intermittents and out-of specification sensors. See appropriate SCAN DATA table under SCAN TESTER - TEST DATA PARAMETERS in 3.0L VIN (L) & 3.8L VIN (3 & 7) TESTS W/CODES article.

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

Diagnostic Circuit Check. Scheme 513

SELF-DIAGNOSTIC SYSTEM

For additional information on the self-diagnostic system and retrieving Diagnostic Trouble Codes (DTC), see SELF-DIAGNOSTIC SYSTEM information in 3.0L VIN (L) & 3.8L VIN (3 & 7) TESTS W/CODES article.

DIAGNOSTIC TROUBLE CODE IDENTIFICATION

DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION

CHART A1 NO "SERVICE ENGINE SOON" LIGHT

"SERVICE ENGINE SOON" (SES) light should be on steady when ignition is on and engine is off. Battery voltage is supplied to bulb. Bulb is grounded by ECM through circuit No. 419.

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

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

Diagnostic Aids

ENGINE RUNS OKAY

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

ENGINE CRANKS, BUT WILL NOT RUN

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

Chart A1 No "Service Engine Soon" Light. Scheme 514

CHART A2, WON'T FLASH CODE 12, SERVICE ENGINE SOON LIGHT ON

"SERVICE ENGINE SOON" light should be on steady when ignition is on and engine is off. Battery voltage is supplied to light bulb and light bulb is grounded by ECM through circuit No. 419. With diagnostic terminal grounded, light should flash a Code 12, followed by any trouble codes stored in memory. A steady light could indicate 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 light goes off when ECM connector is unplugged, circuit No. 419 is not shorted to ground.
2. If there is a problem with ECM that causes "Scan" tester to not read serial data, ECM should not flash a Code 12. If Code 12 is flashed, ensure that "Scan" tester is functioning properly on another vehicle. If "Scan" tester is functioning properly and circuit No. 451 is okay, PROM or ECM may be at fault for "NO ALDL" symptom.
3. This test will check for open diagnostic circuit No.451.
4. At this point, "SERVICE ENGINE SOON" light wiring is okay. Problem is faulty ECM or PROM. If Code 12 does not flash, ECM should be replaced using original PROM. Replace PROM only after trying new ECM, as a defective PROM is an unlikely cause of problem.

Chart A2, Won't Flash Code 12, Service Engine Soon Light On. Scheme 515

CHART A3, ENGINE CRANKS BUT WILL NOT RUN

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

The sequential fuel injection type of fuel delivery system utilizes 6 separate injector "driver" circuits to activate the 6 fuel injectors. While cranking, ECM activates all 6 injector "driver" circuits simultaneously (all at one time). After a calibrated engine RPM is reached and a good camshaft signal has been received by the ECM, 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 that "SES" light operation, TPS, and coolant sensor signals are normal. A blinking injector test light verifies that ECM is monitoring C(3)I reference signal and attempting to pulse injectors.
2. The cam and crank sensors have been verified as functioning properly. Performing a fuel pressure test will differentiate between fuel related or ignition system problem.
3. The 8 terminal injector harness connector must be unplugged to avoid flooding of engine and fouling of spark plugs. By testing for spark on plug leads 1, 3 and 5, each ignition coil's ability to produce at least 25,000 volts is verified.
4. Checking faulty coil's control circuit using a test light, will determine whether coil is faulty, or module's internal driver for that coil is at fault.
5. This test checks for battery voltage at circuit No. 1039. If voltage was present, "light off" test result was caused by no activation pulse reaching injector connector from ECM.
6. If fuse was blown, check circuit No. 839, which includes fuel pump relay, fuel pump and wiring, to determine cause of high current flow.
7. Test light to 12 volts simulates a reference signal to the ECM. This results in an injector test light flash with each contact of the test light probe to terminal "D". Various injector clicks (pulses) will be heard. It may take up to 3 probe contacts to flash test light. If test light flashes, circuit No. 430, ECM and injector driver circuits are functioning properly.
8. If crank sensor signal circuit terminal "A" is momentarily jumpered to ground circuit terminal "C", and engine is cranked without turning ignition off, the response should be an injector test light flash. This is due to an artificial "Sync Signal" being transmitted to C(3)I module. This allows generation of the 3x reference signal to ECM terminal "BD8", and ECM to activate injector driver circuit.
9. This test verifies proper sync signal circuit voltage of 6-9 volts, and a proper ground from C(3)I module to terminal "C" of sensor connector.
10. Determines if reason for incorrect voltage reading was due to fault in circuit No. 645 or faulty C(3)I module.
11. Jumping the crank sensor harness terminals "A" and "C" together, this simulates a sync signal to the C(3)I module. By jumping the crank sensor harness terminals "B" and "C" together, a crank signal is simulated. This signal will then cause the ECM to energize the fuel pump relay for 2 seconds (an audible clicking on and off should be noticed), also you should be able to hear several, if not all the injectors, activate.
12. Verifies a proper crank signal circuit voltage of 6-9 volts and a good ground from the C(3)I module to terminal "C" of sensor connector.
13. 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 C(3)I module.

Chart A3, Engine Cranks But Will Not Run (1 Of 4). Scheme 516

Chart A3, Engine Cranks But Will Not Run (2 Of 4). Scheme 517

Chart A3, Engine Cranks But Will Not Run (3 Of 4). Scheme 518

Chart A3, Engine Cranks But Will Not Run (4 Of 4). Scheme 519

CHART A5, FUEL SYSTEM ELECT. TEST (NON-DIGITAL CLUSTER)

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

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

1. Cranks, but won't run.
2. Code 44 or 45.
3. Cuts out, may feel like ignition problems.
4. Hesitation, loss of power and poor fuel economy. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. If fuse is blown, a short to ground in circuits No. 120 and 839, or fuel pump itself is the cause.
2. Determines if fuel pump circuit is being controlled by the ECM. ECM should energize fuel pump relay. Since engine is not cranking or running, ECM should de-energize relay within 2 seconds after ignition is turned on.
3. Turns on fuel pump if circuit No. 120 wiring is okay. If pump runs, problem is in basic fuel delivery.
4. This test will determine if short to ground on circuit No. 120 caused fuse to blow. To prevent misdiagnosis, ensure that fuel pump is disconnected before proceeding with test.
5. Checks for short to ground in fuel pump relay harness circuit No. 839.
6. Checks for open in the fuel pump relay ground, circuit No. 450.
7. Determines if the ECM is in control of the fuel pump relay through circuit No. 465 (terminal "A").
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 of oil pressure and provides a second battery feed path to the fuel pump. If the relay fails, the pump will run using the battery feed supplied by the closed oil pressure switch. This step checks the oil pressure switch to ensure it provides battery feed to the fuel pump should the pump relay fail. A failed pump relay will result in extended engine crank time because of the time required to build enough oil pressure to close the switch. This, or a faulty oil pressure switch can result in "Engine Cranks But Won't Run".

Chart A5, (1 Of 2) Fuel System Elec Test (Non-Dig Cluster). Scheme 520

Chart A5, (2 Of 2) Fuel System Elec Test (Non-Dig Cluster). Scheme 521

CHART A5, FUEL SYSTEM ELECT. TEST (DIGITAL CLUSTER)

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

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

1. Cranks, but won't run.
2. Code 44 or 45.
3. Cuts out, may feel like ignition problems.
4. Hesitation, loss of power and poor fuel economy. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. If fuse is blown, a short to ground in circuits No. 120 and 839, or fuel pump itself is the cause.
2. Determines if fuel pump circuit is being controlled by the ECM. ECM should energize fuel pump relay. Since engine is not cranking or running, ECM should de-energize relay within 2 seconds after ignition is turned on.
3. Turns on fuel pump if circuit No. 120 wiring is okay. If pump runs, problem is in basic fuel delivery.
4. This test will determine if short to ground on circuit No. 120 caused fuse to blow. To prevent misdiagnosis, ensure that fuel pump is disconnected before proceeding with test.
5. Checks for short to ground in fuel pump relay harness circuit No.839.
6. Checks for open in relay ground circuit No. 450.
7. Determines if ECM is controlling fuel pump relay through circuit No. 465 (terminal No. 5).
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 relay fails, fuel pump will continue to run using current supplied by closed oil pressure switch. This test checks oil pressure switch to ensure it provides power to fuel pump, should pump relay fail.

Chart A5,(1 Of 2) Fuel System Elect. Test (Dig Cluster Only). Scheme 522

Chart A5,(2 Of 2) Fuel System Elect. Test (Dig Cluster Only). Scheme 523

CHART A7, FUEL PRESSURE TEST

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

1. Cranks but won't run.
2. Code 44 or 45. NOTE: Test numbers refer to test numbers on diagnostic chart. WARNING: To reduce the risk of vehicle fire and/or personal injury, it is advised that the fuel system pressure be relieved before servicing fuel system components.

1. Install Fuel Pressure Gauge (J-34730-1) to pressure tap. Wrap a shop towel around fuel pressure gauge tap to absorb any small amount of fuel leakage that may occur when installing gauge. Connect fuel tank harness connector. Start engine. With ignition on and engine running, pump pressure is regulated by spring pressure and throttle body vacuum within the pressure regulator assembly. Turn ignition off for 10 seconds. Pressure should not leak down after fuel pump is shut off.
2. When engine is idling, vacuum is high and is applied to the fuel pressure regulator diaphragm. This will overcome regulator spring pressure, resulting in a lower fuel pressure.
3. The application of 12-14 in. Hg vacuum to the pressure regulator should result in reduced fuel pressure.
4. Fuel pressure that leaks down may be caused by one of the following conditions: In-tank fuel pump check valve not holding. Pump coupling hose leaking. Fuel pressure regulator valve leaking. Injector sticking open.
5. If fuel system has pressure, but 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 operate lean and may set Code 44. Also, hard starting cold and overall poor performance condition may exist. 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 pressure drop occurs only while driving, engine will normally surge and shut off as pressure begins to drop rapidly.
6. Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to the pump test terminal, pressure should be greater than 75 psi (5.2 kg/cm 2 ).
7. This test determines if high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.

Chart A7, (1 Of 2) Fuel Pressure Test. Scheme 524

Chart A7, (2 Of 2) Fuel Pressure Test. Scheme 525

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, depending on engine or tool used.

Check at O2 Sensor

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

Diagnosis

1. Start engine and bring to operating temperature. Raise engine speed to 2500 RPM and observe exhaust system backpressure gauge. Reading should not exceed 1.25 psi (.09 kg/cm 2 ).
2. If during step 1), specification is exceeded, exhaust system restriction is indicated.
3. Check complete exhaust system for collapsed pipe, heat distress and possible internal muffler failure.
4. If none of the conditions in step 4) exist, check for restricted catalytic converter. Replace if necessary.

Chart B1, Restricted Exhaust System Check. Scheme 526

CHART C2, IDLE AIR CONTROL (IAC) VALVE CHECK

The ECM controls idle RPM using the IAC valve. To increase idle RPM, the ECM retracts the IAC, allowing more air to pass around throttle plate. To decrease RPM, ECM extends IAC valve, reducing airflow around throttle plate. The "Scan" tester will read ECM commands to 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 engine was stopped, IAC valve is retracted (more air) to a fixed "Park" position for increased airflow and idle speed during next engine start. A "Scan" tester will display 100 or more counts.
3. Ensure that IAC valve is disconnected prior to this test. Test light will confirm 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. Unplug ECM and 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. If idle is too high, stop engine. With ignition on, ground diagnostic terminal and wait 30 seconds for IAC to seat, and disconnect IAC. Unground diagnostic terminal and start engine. If idle speed is more than 750-850 RPM, locate and correct vacuum leak. For other causes of an improper idle, check the following

1. System Too Lean - Idle speed may be too high or too low, or engine running speed may vary up and down, and unplugging IAC does not help. A Code 44 may have been set. The "Scan" tester will read an oxygen sensor output less than .3 volt. Check for low regulated fuel pressure or water in fuel. A lean exhaust, with an oxygen sensor output fixed greater than .8 volts, indicates 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 C2, Idle Air Control (IAC) Valve Check. Scheme 527

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.

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

Chart C2A, Injector Balance Test. Scheme 528

CHART C3, CANISTER PURGE CHECK

Canister purge is controlled by a solenoid that allows manifold vacuum to purge the canister when energized. The ECM supplies a ground to energize the solenoid (purge on). The purge solenoid is energized (purge on) if the diagnostic test terminal is grounded with the engine stopped or if following conditions are met

1. Engine run time is more than one minute.
2. Coolant temperature more than 176°F (80°C).
3. Vehicle speed more than 5 MPH
4. Throttle position voltage greater than .75 volt. NOTE: Test numbers refer to test numbers on diagnostic charts.

1. Checks to see if solenoid is opened or closed. Solenoid is normally de-energized in this test, indicating it should be closed.
2. This test completes functional check by grounding test terminal. This should normally energize solenoid and allow vacuum to drop (purge on).
3. This test checks for open or shorted solenoid circuit.

Chart C3, Canister Purge Check. Scheme 529

CHART C4F1, C(3)I MISFIRE AT IDLE

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

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

1. If misfire problem exists under load only, see CHART C4F2. Engine RPM should drop equally on all plug leads.
2. Spark Tester (ST-125) must be used because it is essential to verify adequate available secondary voltage (25,000 volts) at spark plug.
3. By grounding opposite plug lead of the affected coil, a faulty spark plug (extremely high resistance) may be detected.
4. If ignition coils are carbon tracked, the coil tower spark plug wire nipples may be damaged.
5. By switching a normally operating coil into the position of the malfunctioning one, a determination can be made as to fault being the coil or ignition module.

Chart C4F1, C(3)I Misfire At Idle. Scheme 530

CHART C4F2, C(3)I MISFIRE UNDER LOAD

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

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

1. If the misfire problem exists at idle only, see CHART C4F1. 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.
2. By grounding the opposite plug lead of the affected coil, a faulty spark plug (extremely high resistance) may be detected.
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.

Chart C4F2, C(3)I Misfire Under Load. Scheme 531

CHART C5, ELECTRONIC SPARK CONTROL (ESC) SYSTEM CHECK

The knock sensor is used to detect engine detonation and ECM will retard the electronic spark timing based on signal being received. The circuitry, within the knock sensor, causes ECM's supplied 5-volt signal to be pulled down so that under a no knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal, which rides on the 2.5 volts (DC voltage). The amplitude and frequency are dependent upon the knock level.

The MEM-CAL used with this engine, contains functions which were part of remotely mounted ESC modules used on other GM vehicles. The ESC portion of the MEM-CAL, sends a signal to other parts of the ECM which adjusts spark timing to retard spark and reduce detonation.

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

1. With engine idling, there should not be a knock signal present at ECM, because detonation is not likely to occur under no load condition.
2. Tapping engine lift hook should simulate a knock signal to determine if sensor is capable of detecting detonation. If no knock is detected, try tapping on engine block closer to sensor before replacing sensor.
3. If engine has an internal problem which is creating a knock, knock sensor may be responding to internal failure.
4. This test determines if knock sensor is faulty or if ESC portion of MEM-CAL is faulty. If it is determined that MEM-CAL is faulty, ensure that it is properly installed and latched into place. If not properly installed, repair and retest.

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

Chart C5, Electronic Spark Control (ESC) System Check. Scheme 532

CHART C7, EXHAUST GAS RECIRCULATION (EGR) FLOW CHECK

The digital (EGR) valve is designed to accurately supply EGR to an 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 a solenoid is energized, the armature, with attached shaft and swivel pintle, is lifted opening the orifice. The flow accuracy is dependent on metering orifice size only, which results in improved control.

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

If a code is set, inspect EGR for damage. Unplug 4 wire connector at EGR. Install a fused jumper from battery to terminal "D" of EGR. Start and idle engine. Using a jumper, ground terminals "A", "B" and "C" one at a time. You should be able to discern a change in engine RPM as terminal is grounded. Terminal "A" should result in a small change and "C" in a large change in RPM. Engine may stall when "C" is grounded.

Chart C7, Exhaust Gas Recirculation (EGR) Flow Check. Scheme 533

Chart C7, Exhaust Gas Recirculation (EGR). Scheme 534

CHART C8A, TORQUE CONVERTER CLUTCH (TCC) (1 OF 2)

The purpose of the torque converter clutch is to eliminate the power loss of the torque converter when vehicle is in cruise condition. This allows the convenience of automatic transmission and fuel economy of a manual transaxle. The heart of the system is a solenoid located inside the transaxle which is controlled by the ECM. When solenoid coil is activated (on), the torque converter clutch is applied which results in straight through mechanical coupling from engine to drive wheels. When the transaxle (TCC) solenoid is deactivated, the torque converter clutch is released which allows the torque converter to operate in the conventional manner (fluid coupling between engine and transaxle).

TCC will engage under the following conditions

1. Engine warmed to operating temperature.
2. Vehicle speed greater than a calibrated value (about 28 MPH).
3. TPS output not changing, indicating a steady road speed.
4. Brake switched closed. NOTE: Test numbers refer to test numbers on diagnostic charts.

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

The "Scan" tester only indicates when ECM has turned on TCC driver, and this does not confirm that TCC has engaged. To determine if TCC is functioning properly, road test vehicle. Engine RPM should decrease when "Scan" tester indicates TCC driver has turned on.

Chart C8A, (1 Of 2) Torque Converter Clutch (TCC). Scheme 535

CHART C8A, TORQUE CONVERTER CLUTCH (TCC) (2 OF 2)

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

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

1. Some "Scan" testers display the state of these switches in different ways. Read instructions on "Scan" tester usage before proceeding with test procedures. Since both switches should be in closed state during this test, "Scan" tester should indicate same readings for 2nd, 3rd or 4th gear switches.
2. Determines whether switch or signal circuit is open. The circuit can be checked for an open by measuring voltage at TCC connector. Reading should be about battery voltage. Because switch or switches should be grounded at some point in this procedure, unplugging TCC connector should cause "Scan" tester switch state to change. The switch state should change when vehicle shifts into 3rd gear.

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

Chart C8A, (2 Of 2) Torque Converter Clutch (TCC). Scheme 536

CHART C10A, A/C CLUTCH CONTROL (1 OF 2)

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 A/C clutch during WOT operation. The A/C clutch control relay is energized when ECM provides a ground path for circuit No. 366.

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

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

Chart C10A, (1 Of 2) A/C Clutch Control. Scheme 537

CHART C10A, A/C CLUTCH CONTROL (2 OF 2)

The A/C relay is ECM controlled to delay A/C clutch engagement .4 second after A/C is turned on. This allows the IAC to adjust engine RPM before A/C clutch engages. The ECM also causes the relay to disengage A/C clutch during Wide Open Throttle (WOT). 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 for battery voltage to relay through circuit No. 67.
2. Substitutes for relay to determine if problem is in relay or in circuit No. 59, A/C clutch coil, high pressure switch or ground.
3. Checks for open in circuit No. 67 between cycling switch and A/C fuse, or open circuit No. 67 to relay.
4. Checks to see 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 cycling switch and ECM.

Chart C10A, (2 Of 2) A/C Clutch Control. Scheme 538

CHART C12A, COOLANT FAN CHECK

Power for the fan is supplied through the fusible link to terminal No. 1 on all relays. The relays are energized when ECM (quad drivers) ground circuit.

1. Low speed relay - The ECM energizes the relay through terminal "YC2" when coolant temperature reaches 208°F (101°C).
2. High speed relay - The high speed relay is energized by the ECM or the A/C pressure switch. 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 will be energized. NOTE: Test numbers refer to test numbers on diagnostic charts.

1. Grounding the diagnostic test terminal should cause the ECM to ground circuit No. 535 and fan to run at low speed.
2. Grounding coolant temperature switch harness terminal will check circuit No. 536, and will also check high speed fan control relay.
3. Separates and checks ECM driver circuit and relay to fan circuit, for an open circuit or faulty relay.
4. This test checks to see if coolant temperature switch is grounding and is grounded when light comes on. The switch should close at 226°F (108°C).
5. This will check A/C pressure switch and related wiring from switch, to the fan control relay. If poor A/C performance is noted, A/C pressure switch should be checked by a qualified A/C repair technician. The low speed fan should come on, if high pressure exceeds 260 psi (17.8 kg/cm 2 ).

Chart C12A, Coolant Fan Check. Scheme 539

CHART C12B, COOLANT FAN CHECK

Power for the fan is supplied through the fusible link to terminal No. 1 on all relays. The relays are energized when ECM (Quad Drivers) ground circuit.

1. Low speed relay - The ECM energizes the relay through terminal "YC2" when coolant temperature reaches 208°F (101°C).
2. High speed relay - The high speed relay is energized by the ECM or the A/C pressure switch. 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 will be energized. NOTE: Test numbers refer to test numbers on diagnostic charts.

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

Chart C12B, Coolant Fan Check. Scheme 540

CHART C12C, COOLANT FAN CHECK

Power for the fan is supplied through the fusible link to terminal No. 1 on all relays. The relays are energized when ECM (Quad Drivers) ground circuit.

1. Low speed relay - The ECM energizes the relay through terminal "YC2" when coolant temperature reaches 208°F (101°C).
2. High speed relay - The high speed relay is energized by the ECM or the A/C pressure switch. 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 will be energized. NOTE: Test numbers refer to test numbers on diagnostic charts.

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

Chart C12C, Coolant Fan Check. Scheme 541

CODE 13, OPEN OXYGEN SENSOR CIRCUIT

The ECM supplies a voltage of about .45 volt between terminals "YD2" and "YD3". If measured with 10-megohm digital voltmeter, this may read as low as .32 volt. The oxygen sensor varies the voltage within a range of about one volt if exhaust is rich, down through about .10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation.

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

1. Code 13 will set if following conditions occur: Engine is at operating temperature. More than 40 seconds of engine running time after start. Oxygen signal steady between .35 and .55 volt. TPS signal greater than .55 volt. All conditions must be met for about 30 seconds. If all conditions for a Code 13 exist, system will not go into "closed loop".
2. This test will determine if sensor or wiring is the cause of 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, ECM voltage on circuit No. 412 will be greater than .6 volt.

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 backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness. If connections and harness checks out okay, "Scan" oxygen sensor voltage while moving related connectors and wiring harness. Engine should be warm, running at part throttle in "closed loop". If failure is induced, 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 location of the problem.

Code 13, Open Oxygen Sensor Circuit. Scheme 542

CODE 14, COOLANT TEMP. CIRCUIT HIGH TEMP. INDICATED

The coolant temperature sensor uses a thermistor to control monitored voltage to the ECM. The ECM applies and monitors a voltage on circuit No. 410 to the sensor. When the engine is cold, sensor resistance is high, therefore ECM will see high monitored voltage. As 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 282°F (130°C) for .4 seconds.
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, ECM will use 119°F (48.5°C) as a preprogrammed reference temperature for fuel control.

The "Scan" tester displays engine temperature in degrees centigrade. After engine is started, 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 terminal "YD4", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittent - If connections and harness checks out okay, use "Scan" tester to check coolant temperature reading while moving related connectors and wiring harness. If failure is induced, coolant temperature display will change. This may help to isolate location of malfunction.
3. Shifted Sensor - The TEMPERATURE TO-RESISTANCE VALUES table may be used to test coolant sensor at various temperature levels in order to evaluate the possibility of a shifted (out-of calibration) sensor, which may result in driveability problems.

Code 14, Coolant Temperature Circuit High Temp Indicated. Scheme 543

CODE 15, COOLANT SENSOR SIGNAL, LOW TEMPERATURE INDICATED

The coolant temperature sensor uses a thermistor to control the monitored voltage to ECM. ECM applies and monitors a voltage on circuit No. 410 to the sensor. When engine is cold, sensor resistance is high and ECM sees a high monitored voltage. As the engine reaches operating temperature, sensor resistance becomes less and monitored voltage drops. At operating temperature, voltage will measure about 1.5-2.0 volts at the ECM.

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

Note. The "Scan" tester reads engine temperature in degrees centigrade.

1. Code 15 will set if monitored voltage indicates a coolant temperature less than -40°F (-40°C) for at least 2 seconds.
2. This test simulates a Code 14. If ECM recognizes low monitored voltage, (high temperature) and "Scan" tester reads 130°C, ECM and wiring are okay.
3. This test will determine if circuit No. 410 is open. Using a digital volt/ohmmeter, ensure that 5 volts is present at sensor connector. If Code 15 is set, ECM will use a preprogrammed value of 119°F (48.5°C), for fuel control.

After engine is started, 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 insulation. Check the following conditions

1. Poor Connection - Inspect ECM harness connectors for backed out terminal "YD4", 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 failure is induced, coolant temperature display will change. This may help to isolate location of malfunction.
3. Shifted Sensor - The TEMPERATURE TO-RESISTANCE VALUE table may be used to test 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 circuits No. 410 or 452 will result in a Code 15. If Code 23 is also set, check circuit No. 452 for faulty wiring or connections. Check terminals at sensor for good contact.

Code 15, Coolant Sensor Signal, Low Temperature Indicated. Scheme 544

CODE 16, SYSTEM VOLTAGE HIGH

The ECM monitors battery voltage on circuit No. 440 to terminals "BB1" "BC16". If ECM detects voltage greater than 16 volts, it will turn SES light on and set a Code 16 in memory.

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

1. Test generator output to determine proper operation of the voltage regulator. Run engine at moderate speed and measure voltage across battery. If greater than 16 volts, repair generator.

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

1. Poor connection or damaged harness. Inspect ECM harness connectors for backed out terminal "BC16" or "BB1", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent test. If connections and harness checks okay, monitor battery voltage display while moving related connectors. If failure is induced, battery voltage will abruptly change. This may help to isolate location of malfunction. An engine stall while manipulating harness indicates that the ECM has lost voltage at terminal "BC16" or "BB1". Check for loose connectors in circuit No. 440.

Note. Charging battery using a battery charger and starting the engine at the same time, may set a Code 16.

Code 16, System Voltage High. Scheme 545

CODE 21, TPS SIGNAL VOLTAGE HIGH

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

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

1. Code 21 will set under the following conditions: Engine is running and airflow is less than 15 gm/sec. TPS signal voltage is greater than 2.5 volts. Code 33 or 34 not present at first start up. All conditions met for 5 seconds. With closed throttle, ignition on or engine at idle, voltage at terminal "YD13" should be .36-.44 volt. If not, TPS should be adjusted to specification.
2. With TPS sensor unplugged, TPS voltage should go low if ECM and wiring is okay.
3. Probing circuit No. 452 with a test light checks sensor ground circuit. A faulty sensor ground circuit will cause a Code 21.

A "Scan" tester reads throttle position in volts. With closed throttle, ignition on or at idle, voltage should be .36-.44 volt. If not, adjust TPS to specification. Also some "Scan" testers will read throttle angle as percentages (zero percent equals closed throttle and 100 percent equals WOT). An open in circuit No. 452 will result in a Code 21. Check for the following conditions

1. Poor connections or damaged harness. Inspect ECM harness connectors for backed out terminal "YD13", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connections and damaged harness.
2. Intermittent test. If connections and harness checks out okay, monitor TPS voltage on "Scan" tester while moving related connectors and wiring harness. If failure is induced, TPS display will change. This may help to isolate location of 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 WOT position.

Code 21, TPS Signal Voltage High. Scheme 546

CODE 22, TPS SIGNAL VOLTAGE LOW

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

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

1. Code 22 will set if engine is running and TPS signal voltage is less than .2 volt for 4 seconds.
2. Simulates Code 21. If ECM recognizes high signal voltage, ECM and wiring are okay.
3. With closed throttle, ignition on or engine at idle, voltage at terminal "YD13" should be .36-.44 volt. If voltage is not okay, check TPS adjustment.
4. Simulates a high signal voltage. Checks circuit No. 417 for open.

The "Scan" tester reads throttle position in volts. Voltage should increase at a steady rate as throttle is moved from WOT. Some testers may also read throttle angle in percent (zero percent at closed throttle, 100 percent at wide open throttle). An open or short to ground in circuits 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 terminal "YD13", 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 out okay, monitor TPS voltage using "Scan" tester while moving related connectors and wiring harness. If failure is induced, TPS display will change. This may help to isolate location of 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 Voltage Low. Scheme 547

CODE 23, MAT SENSOR SIGNAL VOLTAGE HIGH

The Manifold Air Temperature (MAT) sensor uses a thermistor to control monitored voltage to the ECM. ECM applies and monitors about 5 volts on circuit No. 472 to sensor. When air temperature is cold, sensor resistance is high, therefore, ECM will see a high monitored voltage. If air temperature is warm, sensor resistance is low and ECM will see low monitored voltage.

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

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

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 wiring and ECM are okay.
2. If resistance is greater than 25,000 ohms, replace sensor.

Code 23, MAT Sensor Signal Voltage High. Scheme 548

CODE 24, VEHICLE SPEED SENSOR (VSS) CIRCUIT

Vehicle speed information is provided to the ECM by the vehicle speed sensor, a permanent magnet (PM) generator mounted in the transmission. The PM generator produces a pulsing voltage whenever vehicle speed is greater than about 3 MPH. The AC voltage level and the number of pulses increases with vehicle speed. The ECM converts the pulsing voltage to MPH, and the MPH can be displayed with a "Scan" tester.

The function of the VSS buffer, used in their past model years, has been incorporated into the ECM. The ECM supplies the necessary signal for the instrument panel (4004 pulses per mile) for operating the speedometer and the odometer.

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

1. Code 24 will set if vehicle speed signal equals zero MPH when: Engine speed is between 1500 and 4000 RPM. TPS reading shows closed throttle. Low load condition (low air flow). Not in park or neutral. No Code 29 or 31. When vehicle is in 4th gear. All conditions met for 20 seconds. Disregard Code 24 that sets when drive wheels are not rotating. The PM generator only produces a signal if drive wheels are rotating faster than 3 MPH.
2. Before replacing the ECM, check MEM-CAL for correct application.

"Scan" tester should indicate a vehicle speed whenever drive wheels are rotating faster than 3 MPH. Check circuit No. 400 and 401 for proper connections. Ensure they are clean and tight, and harness is routed correctly. See INTERMITTENTS in TROUBLE SHOOTING section.

Code 24, Vehicle Speed Sensor (VSS) Circuit. Scheme 549

CODE 25, MAT SENSOR CIRCUIT (HIGH TEMP INDICATED)

The MAT sensor is a thermistor. ECM applies voltage (about 5 volts) on circuit No. 472 to sensor. When air temperature is cold, sensor (thermistor) resistance is high, therefore, the ECM will measure a high monitored voltage. If temperature air is warm, sensor resistance is low, ECM will measure a low voltage.

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

Code 25 will set if

1. Signal voltage indicates manifold air temperature greater than 275°F (135°C).
2. A vehicle speed is present.
3. Both of the above requirements are met for at least 30 seconds.

Due to the conditions necessary to set a Code 25, SES light will only stay on while fault is present.

1. A "Scan" tester may not be used to diagnose this fault, due to ECM transmitting default (substitute) values, when fault is present. If voltage is greater than 4 volts, ECM and wiring are okay.
2. If resistance is less than 185 ohms, replace sensor.

Code 25, Manifold Air Temperature (Mat) Sensor Circuit. Scheme 550

CODE 26, QUAD DRIVER MODULE (QDM) ERROR

Note. This procedure has been revised. See appropriate TECHNICAL SERVICE BULLETIN article in the TECHNICAL SERVICE BULLETIN Section. The Technical Service Bulletin numbers are as follows: Oldsmobile 88-T-08, Pontiac 88-6-7, Buick 88-6E-2.

The ECM is used to control several components such as those illustrated in the mini circuit schematic. ECM controls these devices through the use of a QDM. When the ECM is commanding a component on, the voltage potential of the output circuit will be low (near zero volts). When the ECM is commanding the output circuit to a component off, the voltage potential of the circuit will be high (near battery voltage). The primary function of the QDM is to supply the ground for the component being controlled.

Each QDM has a fault line which is monitored by the ECM. The fault line signal is available on the data stream for "Scan" tester equipment. The ECM will compare the voltage at the QDM based on accepted values of fault line. If the QDM fault detection circuit senses a voltage other than the accepted value, the fault line will go from a low signal on the data stream, to a high signal and a Code 26 will set if applicable. Some QDM circuits will switch from low to high normally. Examples

QDM No. 2, if A/C pressure switch closes and turns on high speed coolant fan or QDM No. 3, if brake is depressed. These conditions are normal and no Code 26 is set. These are accepted conditions. A fault on QDM No. 2 will not set a Code 26, but diagnosis may be done by ensuring A/C is turned off.

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

1. 1) The ECM does not know which controlled circuit caused the Code 26 so this chart will go through each of the circuits to determine which is at fault. This test checks the SES light driver and the SES light circuit.
2. 1A) If hot light and SES light do not illuminate, check for blown 20 amp fuse. If SES light is on and hot light is off, check for burned out bulb or open in circuits No. 39 and/or 35. If circuits and ECM connections are okay, ECM is faulty and must be replaced.
3. 1B) Using "Scan" tester, check coolant parameter for high temperature signal. If tester does not indicate temperature greater than 282°F (130°C), check for grounded circuit No. 35 between hot light and ECM. If circuit is okay, ECM is faulty and must replaced.
4. 2) QDM fault symptoms: * TCC inoperative, Code 39. * EGR inoperative, Codes 63, 64 & 65. * Hot light, on all the time, off during bulb check. * Coolant fan on low speed all the time of won't come on at all.
5. Poor driveability due to 100 percent canister purge.
6. 3) This test will determine which circuit is out of specification. All circuits, except "YC11", SES light, "YC9", and hot light, should be battery voltage when key is on, engine not running. The diagnostic test terminal is not grounded.
7. 4) This test will determine if problem is the circuit of the component. As factory installed ECM is protected with an internal fuse, it is highly unlikely that ECM needs replacement.

Monitor the voltage at each terminal while moving related harness connectors, including ECM harness. If failure is induced, voltage will change. This may help locate the intermittent. Check for bent pins at ECM and ECM connector terminals. If code is reset with no apparent connector problem, replace ECM.

Code 26, (1 of 3) Quad Driver Module (QDM) Error. Scheme 551

Code 26, (2 of 3) Quad Driver Module (QDM) Error. Scheme 552

Code 26, (3 of 3) Quad Driver Module (QDM) Error. Scheme 553

CODE 27, 28 & 29, 2ND, 3RD, 4TH GEAR SWITCH DIAGNOSIS

Gear switches are located inside the transaxle. They are pressure operated switches, that are normally closed. The ECM supplies 12 volts through each selected circuit to switch. In any condition other than the specific gear application, signal line monitors low voltage or low potential. As road speed increases, hydraulic pressure is applied to specific gear clutches, and gear switch opens. During this time, ECM monitors high 12-volt potential and interprets this to indicate that gear is applied. The ECM uses gear signals to control fuel delivery (and TCC).

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

Code 27 will set under the following conditions

1. Circuit No. 581 indicates grounded or closed switch when vehicle is in 4th gear operation.
2. Circuit No. 581 indicates an open (drive) when the engine is first started. Code 28 will set under the following conditions
3. Circuit No. 108 indicates grounded or closed switch when vehicle is in 4th gear operation.
4. Circuit No. 108 indicates an open (drive) when the engine is first started. Code 29 will set under the following conditions
5. Circuit No. 446 indicates grounded or closed switch when vehicle is in 4th gear operation.
6. Circuit No. 446 indicates an open (drive) when the engine is first started.

1. Digital Volt/Ohmmeter (DVOM) must be used. A test light will not light due to the very low current being supplied by the ECM.
2. Checks to see if circuit is grounded through switch.
3. Checks for a good, properly operating switch. Also checks circuit within transaxle for an improper ground.

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

1. Poor Connection, at ECM pins. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to- wire connection.
2. Mis-routed Harness. Inspect wiring harness to ensure that it is not too close to high voltage wires, such as spark plug leads.
3. Damaged Harness. Inspect harness for damage. If harness appears okay, "Scan" while moving related connectors and wiring harness. A change in display would indicate the intermittent fault location.

Code 27, 28 & 29, 2nd, 3rd, 4th Gear Sw. Diagnosis, Flow Chart. Scheme 554

Code 27, 28 & 29, 2nd, 3rd, 4th Gear Sw. Diagnosis Schematic. Scheme 555

CODE 31, PARK/NEUTRAL SWITCH CIRCUIT

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

Code 31 will set under the following conditions

1. If circuit No. 434 indicates P/N (grounded) while in drive range and 4th gear TCC engaged, EGR would be inoperative, resulting in possible detonation.
2. If circuit No. 434 indicates drive (open) at start-up, a drop in idle may exist when gear selector is moved into drive range.
3. If transaxle 4th gear switch has an intermittent open, ECM thinks vehicle is in 4th gear and will set Code 31. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. Checks for a closed switch to ground in "PARK" position. Different types of "Scan" testers will read P/N differently. Refer to "Scan" tester operators manual for type of display used for specific tester.
2. Checks for an open switch in drive range.
3. Ensure "Scan" tester indicates Drive, even while wiggling shifter. This will test for an intermittent or misadjusted switch in Drive or Overdrive range.

Code 31, Park/Neutral Switch Circuit. Scheme 556

CODE 34, MASS AIRFLOW (MAF) SENSOR CIRCUIT

The Mass Airflow (MAF) sensor measures the flow of air which passes through it in a given time. The ECM uses this information to monitor the operating condition of the engine for fuel delivery calculations. A large quantity of air movement indicates acceleration, while a small quantity indicates deceleration or idle. The MAF sensor produces a frequency signal, which cannot be easily measured. The sensor can be diagnosed using the procedures in this chart. Code 34 will set, when either of the following sets of conditions exists

1. Engine running.
2. No MAF sensor signal for 250 mS.
3. Above conditions 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 connector terminal "A" of less than 4 volts 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 circuit are available.

Check for the following

1. Poor Connection, at ECM pin "YD10". Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connection.
2. Mis-routed Harness. Inspect MAF sensor harness to ensure that it is not too close to high voltage wires, such as spark plug leads.
3. Damaged Harness. Inspect harness for damage. If harness appears okay, "Scan" tester while moving related connectors and wiring harness. A change in display would indicate the intermittent fault location.

Code 34, Mass Airflow (MAF) Sensor Circuit. Scheme 557

CODE 38, BRAKE SWITCH CIRCUIT

The ECM monitors the status of brake switch circuits through ECM terminal "BC4". Code 38 will set under the following conditions

1. Code 24 is not present.
2. Vehicle speed has been greater than 35 MPH and back to zero MPH several times.
3. Status of circuit No. 420 has not changed state (high or low). NOTE: Test numbers refer to test numbers on diagnostic chart.

1. This step checks for battery voltage available for circuit No. 420.
2. Checks fuse, switch and circuit for battery voltage.

Code 38, Brake Switch Circuit. Scheme 558

CODE 39, TORQUE CONVERTER CLUTCH (TCC) CIRCUIT

The ECM controls TCC operation by grounding circuit No. 422 through the QDM. Code 39 will set under the following conditions

1. Code 29 is not present.
2. Brake switch is closed (off).
3. TCC is commanded by ECM.
4. Vehicle is in 4th gear.
5. The engine speed to vehicle speed ratio is outside of its window of operation.
6. All of the above for a time greater than 30 seconds.

Code 39, Torque Converter Clutch (TCC) Circuit. Scheme 559

Torque Converter Clutch (TCC). Scheme 560

CODE 41, CAM SENSOR CIRCUIT

Quick reference

1. (Scheme 562)for Code 41 flow chart.
2. (Scheme 561)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 561)for circuit identification.
2. Step validates the integrity of Circuit 630 from the ignition module to the ECM. (Scheme 562)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.

Scheme 561

Scheme 562

Note. When probing connectors to measure voltages, use the connector test adapter kit J-35616 to make connections.

Code 41 Cam Sensor Signal. Scheme 563

CODE 42, EST IGNITION CIRCUIT

The C(3)I module sends a reference signal to the ECM when the engine is cranking. When the engine is running less than 400 RPM, the C(3)I module controls ignition timing. When the engine speed exceeds 400 RPM, the ECM sends a 5 volt signal on the by-pass circuit No. 424 to switch timing to ECM control. An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be restarted but will run on module timing. The following conditions must be met to set a Code 42

1. Engine speed greater than 600 RPM with no EST pulse for 200 mS (open or grounded circuit No. 423).
2. ECM commanding by-pass mode (open or grounded circuit No. 424). NOTE: Test numbers refer to test numbers on diagnostic chart.

1. Checks to see if ECM recognizes a problem. If it does not set Code 42, it is an intermittent problem and could be due to a loose connection.
2. With ECM disconnected, ohmmeter should be reading less than 200 ohms, which is the normal resistance of EST circuit through C(3)I module. A higher resistance would indicate a fault in circuit No.423, poor C(3)I module connection, or faulty C(3)I module.
3. If test light was on when connected from 12 volts to ECM harness terminal "BC7", either circuit No. 424 is shorted to ground or C(3)I module is faulty.
4. Checks to see if C(3)I module switches when by-pass circuit is energized by 12 volts through test light. If C(3)I module actually switches, ohmmeter reading should shift to greater than 8000 ohms.
5. Unplugging ignition module should cause ohmmeter to read as if it were monitoring an open circuit (infinite reading). If not, 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. Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect ECM harness connectors for backed out terminals "BC7" or "BC8", 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, connect digital voltmeter from affected terminal to ground and move related connectors and wiring harness. If failure is induced, voltage reading will change.

Code 42, EST Ignition Circuit. Scheme 564

CODE 43, ELECTRONIC SPARK CONTROL (ESC) CIRCUIT

The knock sensor is used to detect engine detonation. The ECM will retard electronic spark timing based on the signal being received. The circuitry within the knock sensor causes the ECM's supplied 5 volt signal to be pulled down, so that under a no knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal which rides on the 2.5 volts (DC voltage). The amplitude and signal frequency are dependent upon the knock level.

If circuit No. 496 becomes open or shorted to ground, voltage will either go greater than 3.5 volts or less than 1.5 volts. If either of these conditions are met for about 5 seconds, a Code 43 will stored.

NOTE: Test numbers refer to test numbers on diagnostic chart.

1. Code 43 will set if: Coolant temperature is greater than 90°C. MAT temperature is greater than 0°C. High engine load based on LV8 and RPM. Voltage on circuit No. 496 goes greater than 3.5 volts or less than 1.5 volts. All of above conditions met for 5 seconds. If an audible knock is heard from the engine, repair internal engine problem, normally no knock should be detected at idle.
2. If tapping on engine lift hook does not produce a knock signal, try tapping engine closer to sensor before proceeding.
3. The ECM has a 5 volt pull-up resistor which should be present at knock sensor terminal.
4. This test determines if knock sensor is faulty or if ESC portion of the MEM-CAL is faulty.

Check circuit No. 496 for a potential open or short to ground. Also check for proper installation of MEM-CAL. See INTERMITTENTS in TROUBLE SHOOTING.

Code 43 Schematic, Electronic Spark Control (ESC) Circuit. Scheme 565

Code 43 Flow Chart, Electronic Spark Control (ESC) Circuit. Scheme 566

Code 43 Electronic Spark Control (ESC). Scheme 567

CODE 44, OXYGEN SENSOR CIRCUIT (LEAN EXHAUST INDICATED)

The ECM supplies a voltage of about .45 volt (450 mV) between terminals "YD2" and "YD3". If measured with a 10-megohm digital voltmeter, this may read as low as .32 volt. The O2 sensor varies the voltage within a range of about one volt (1000 mV) if exhaust is rich, down through about .10 volt (100 mV) if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is less than about 600°F (316°C). An open sensor circuit or cold sensor will result in vehicle operating in "open loop". Code 44 is set when the O2 sensor signal voltage on circuit No. 412 remains less than .2 volt for 60 seconds or more, and the system is operating in "closed loop".

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

1. Running the engine at 1000 RPM keeps O2 sensor hot, so an accurate display voltage is maintained.
2. Opening O2 sensor wire should result in a voltage display of between 350 and 550 mV. If display is still fixed less than 350 mV, fault is a short to ground in circuit No. 412 or ECM is faulty.

Diagnostics Aids

Using the "Scan" tester, observe the block learn values at different RPM and airflow conditions. If the conditions for Code 44 exists, the block learn values will be around 150. Check for the following conditions

1. Oxygen sensor pigtail may be mispositioned and contacting exhaust manifold.
2. Check for intermittent ground in wire between connector and sensor.
3. A Mass Airflow (MAF) sensor output that causes ECM to sense a lower than normal airflow will cause the system to go lean. Disconnect MAF sensor and if lean condition is eliminated, replace MAF sensor.
4. Perform injector balance test, see CHART C2A.
5. Water, even in small amounts, near in-tank fuel pump inlet can be delivered to injectors. 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 vehicle at various road speeds and/or loads to confirm problem. See CHART A7.
7. If there is an exhaust leak, engine can cause outside air to be pulled into 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, Oxygen Sensor Circuit (Lean Exhaust Indicated). Scheme 568

CODE 45, OXYGEN SENSOR CIRCUIT (RICH EXHAUST INDICATED)

The ECM supplies a voltage of about .45 volt (450 mV) between terminals "YD2" and "YD3". If measured with a 10-megohm digital voltmeter, this may read as low as .32 volt. The O2 sensor varies the voltage within a range of about one volt (1000 mV) if exhaust is rich, down through about .10 volt (100 mV) if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is less than about 600°F (316°C). An open sensor circuit or cold sensor will result in vehicle operating in "open loop". Code 44 is set when the O2 sensor signal voltage on circuit No. 412 remains greater than .7 volt for 30 seconds and in "closed loop" and engine time after start is one minute or more. Also, if throttle angle is between 3 and 45 percent.

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

Using the "Scan" tester, observe the block learn values at different RPM and airflow conditions. If the conditions for Code 45 exists, the block learn values will be around 115. Check for the following conditions

1. Fuel Pressure. System will go rich if pressure is too high. ECM can compensate for some increase in fuel pressure. If fuel pressure becomes too high, a Code 45 may be set. See fuel system diagnosis in CHART A7.
2. Rich Injector. Perform injector balance test, see CHART C2A.
3. Leaking Injector. See CHART A7 for diagnosis.
4. Check for contaminated fuel.
5. Canister Purge. Check for fuel saturation. If full of fuel, check canister control and hoses. See CHART C3 for diagnosis.
6. MAF Sensor. An output that causes ECM to sense a higher than normal air flow can cause system to go rich. Unplugging MAF sensor will allow ECM to set a fixed value for sensor. Substitute a different MAF sensor if rich condition is rectified while sensor is unplugged.
7. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for raw fuel.
8. TPS. An intermittent TPS output will cause system to go rich, due to a false indication of engine acceleration.
9. EGR. An EGR staying open (especially at idle) will cause the O2 sensor to indicate a rich exhaust, and could result in a Code 45.

Code 45, Oxygen Sensor Circuit (Rich Exhaust Indicated). Scheme 569

CODE 48, MISFIRE DIAGNOSIS

Code 48 will set if following conditions are met

1. TPS is between .8 and 1.07 volts.
2. RPM is between 1100 and 1400.
3. MPH is between 50 and 60.
4. Oxygen sensor cross counts are greater than 20.
5. All of the above for 3 seconds.

Code 48 will set when a problem exists with electrical system, fuel system or a basic engine problem, such as

1. A fuel related problem (such as restricted fuel injector).
2. A problem with ignition system such as bad plug wires, spark plugs or coil pack.
3. Check for other engine related problems such as burned or worn valves, weak valve springs, poor compression, worn camshaft or faulty lifters.

For additional items to check see TROUBLE SHOOTING.

CODE 51, MEM-CAL ERROR

Checks that all pins are fully inserted in socket. If okay, replace PROM, clear memory and recheck. If Code 51 reappears, replace ECM.

CODE 63, 64 & 65, EGR FLOW CHECK

Code 63, 64 and 65 are EGR flow test failures. The ECM, on a closed throttle coast down, will cycle solenoids on and off individually and look for a consequent change in engine RPM and O2 sensor activity.

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

If a code is set, inspect EGR for damage. Unplug 4-wire connector at EGR. Install fused jumper from battery to terminal "D" of EGR. Start and idle engine. Using a jumper, ground terminals "A", "B" & "C" one at a time. You should be able to discern a change in engine RPM as terminal is grounded. Terminal "A" should result in a change, and terminal "C" should result in a substantial change in RPM.

Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect ECM harness connectors for backed out terminals "BC2", "BC3" and "BD2", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test. If connections and harness are okay, monitor to voltage to ECM connectors "BC2", "BC3" and "BD2" while moving related connectors and wiring. If failure is induced, display will change. This may help isolate location of malfunction.

Code 63, 64 & 65, EGR Flow Check Circuit Diagram (3.8L). Scheme 570

Code 63, 64 & 65, EGR Flow Check (3.8L). Scheme 571

C Body 3.8L 3800 (VIN C) PFI Component Locations. Scheme 572

H Body 3.8L 3800 (VIN C) Early Model PFI Comp Location. Scheme 573

H Body 3.8L 3800 (VIN C) Late Model PFI Comp Location. Scheme 574

ECM TERMINAL ID

The following conditions must be met before testing

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

3.8L 3800 (VIN C) PFI ECM Terminal I.D. (1 Of 4). Scheme 575

3.8L 3800 (VIN C) PFI ECM Terminal I.D. (2 Of 4). Scheme 576

3.8L 3800 (VIN C) PFI ECM Terminal I.D. (3 Of 4). Scheme 577

3.8L 3800 (VIN C) PFI ECM Terminal I.D. (4 Of 4). Scheme 578

3.8L 3800 PFI CCC Wiring Diagram. Scheme 579

See also:
• SCAN TESTER - TEST DATA PARAMETERS
• SELF-DIAGNOSTIC SYSTEM
• 13
• 14
• 15
• 16
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 31
• 34
• 38
• 39
• 41
• 42
• 43
• 44
• 45
• 48
• 51
• 63