2.0L VIN [1] Tests W/codes Chevrolet Corsica I

Scheme 32

Scheme 33

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. "Scan" tester or ALDL tool NOT installed

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

TBI Terminal I.D. (2.0L [VIN 1] "J" Body Vehicle. Scheme 34

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. "Scan" tester or ALDL tool NOT installed

Terminal ID & Voltage - White 24 Pin Connector (2.0L - L Body Vehicle). Scheme 35

Terminal ID & Voltage - Black 24 Pin Connector (2.0L - L Body Vehicle). Scheme 36

ECM CCC Wiring Diagram (2.0L - J Body Vehicle). Scheme 37

ECM CCC Wiring Diagram (2.0L - L Body Vehicle). Scheme 38

DIAGNOSTIC CIRCUIT CHECK

The Diagnostic Circuit Check is an organized approach to identifying a problem created by an electronic engine control system malfunction. It must be the starting point for any driveability complaint diagnosis, because it directs the technician to the next logical step in diagnosing the complaint.

After completing the Diagnostic Circuit Check and finding the on-board diagnostics functioning properly and no trouble codes displayed, the appropriate "SCAN DATA" table in TROUBLE SHOOTING may be used for data comparsion. The typical values are an average of display values recorded from normally operating vehicles and are intended to represent what a normally functioning system would typically display.

Note. A "Scan" tester that displays faulty data should not be used, and the problem should be reported to the manufacturer. The use of a faulty "Scan" tester can result in misdiagnosis and unnecessary parts replacement.

Only the parameters listed are used in this article for diagnosis. If a "Scan" tester reads other parameters, the values are not recommended for use in diagnosis. If "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 "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 "M" and ECM.

Diagnostic Circuit Check - Flow Chart. Scheme 39

Chart A1, Schematic - No "Service Engine Soon" Light. Scheme 40

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

1. Checks to determine if fault is in "SERVICE ENGINE SOON" light or ECM.
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

If engine runs okay, check for the following

1. Faulty light bulb.
2. Circuit No. 419 open.
3. Gauge fuse blown. This will result in no stoplights, oil or alternator lights, seat belt reminder, etc.

Chart A1, Flow Chart - No "Service Engine Soon" Light. Scheme 41

Chart A2, Schematic - Won't Flash Code 12, "SES" Always On. Scheme 42

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

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

Chart A2, Flow Chart - Won't Flash Code 12, "SES" Always On. Scheme 43

Chart A3, Schematic - Engine Cranks But Will Not Run. Scheme 44

Note. Before using this chart, check battery condition, engine cranking speed, and fuel quantity. Step numbers refer to step numbers on diagnostic chart.

1. A "SERVICE ENGINE SOON" light on is a basic test to determine if there is a 12-volt supply to ECM. NO ALDL may be due to an ECM problem, and CHART A2 will diagnose the ECM. If TPS is greater than 2.5 volts, the engine may be in the "clear flood" mode, which will cause starting problems. The engine will not start without reference pulses and, therefore, the "Scan" tester should always read RPM (reference) during cranking.
2. 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.
3. While cranking engine, there should be no fuel spray with injector disconnected. If fuel injector sprays or leaks fuel, replace the injector.
4. Using Fuel Injector Test Light (BT 8329), test light should blink, indicating the ECM is controlling the injectors. How bright the light blinks is not important.
5. Fuel spray from the injector indicates that fuel is available, however, the engine could be severely flooded. If no fuel sprays from the injector, this indicates a faulty fuel system or no ECM control of injector system.

1. Water or foreign material can cause a no start condition during freezing weather. The engine may start after 5 or 6 minutes in a heated shop. The problem may not re-occur until an overnight park in freezing temperatures.
2. An EGR valve sticking open can cause a low air/fuel ratio during cranking. Unless engine enters "clear flood" mode at the first indication of a flooding condition, it can result in no start.
3. Low fuel pressure can result in a very lean air/fuel ratio.

Chart A3, Flow Chart-Engine Cranks But Won't (1 OF 3). Scheme 45

CHART A3, ENGINE CRANKS BUT WILL NOT RUN (2 OF 3)

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

1. Because DIS uses 2 plugs and wires to complete the circuit of each coil, the opposite spark plug wire should be left connected.
2. This test will determine if the 12-volt supply and a good ground is available at the DIS ignition module.
3. This test will determine if the ignition module is not generating the reference pulse, or if wiring or ECM are at fault. By touching and removing a test light to 12 volts on circuit No. 430, a reference pulse should be generated. If RPM is indicated, ECM and wiring are okay.
4. This test will determine if the ignition module is not triggering the problem coil or if the tested coil is at fault. This test could also be performed by using another known good coil. Secondary coil resistance should be 5000-10,000 ohms. There should be no continuity between ground and either secondary terminal.
5. A/C voltage should be generated due to the changing flux as the crankshaft slots move past the crankshaft sensor. The following table contains information updated as per Technical Service Bulletin Number 89-6E-28.

NORMAL CRANK SENSOR VOLTAGE OUTPUT RANGE

Chart A3, Flow Chart-Engine Cranks But Won't Run (2 OF 3). Scheme 46

CHART A3, ENGINE CRANKS BUT WILL NOT RUN (3 OF 3)

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

1. Tests to determine if injector has battery voltage.
2. A faulty ECM, may result in damage to the injector.
3. A test light connected from ECM harness terminal "W1" to ground should light due to continuity through the injector.

Chart A3, Flow Chart-Engine Cranks But Won't Run (3 OF 3). Scheme 47

Chart A5, Schematic - Fuel Pump Relay Ckt, "J" Body. Scheme 48

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

1. Determines if oil pressure switch is stuck in the open position.
2. Determines if oil pressure switch is stuck in the closed position.

An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold or engine oil pressure is low. The extended crank period is caused by the time necessary to build enough oil pressure to close the oil pressure switch and turn on the fuel pump.

Chart A5, Flow Chart - Fuel Pump Relay Ckt "J" Body. Scheme 49

Chart A5, Schematic - Fuel Pump Relay Ckt "L" Body. Scheme 50

An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold or engine oil pressure is low. The extended crank period is caused by the time necessary to build enough oil pressure to close the oil pressure switch and turn on the fuel pump. A "Scan" tester set in the "PPSW" position may be used to check the status of the fuel pump relay circuit. Normally, the "PPSW" will read battery voltage for 2 seconds after the ignition is turned on. A reading of zero volts for the first 2 seconds after ignition is turned on would indicate a problem with fuel pump relay or relay drive circuit.

Chart A5, Flow Chart - Fuel Pump Relay Ckt "L" Body. Scheme 51

Chart A7, Fuel System Diagnosis. Scheme 52

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

1. If fuse in jumper wire blows, check circuit No. 120 (between relay and fuel pump) for a short to ground.
2. Pressure, but less than 9 psi (6.3 kg/cm 2 ) falls into 2 categories: Regulated pressure, but less than 9 psi (6.3 kg/cm 2 ) Amount of fuel to injector okay but pressure is too low. System will be running lean and may set Code 44. Also, hard starting cold and poor overall performance. Restricted flow causing pressure drop - Normally, a vehicle with a fuel pressure of less than 9 psi (6.3 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 to zero.
3. Gradually 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 from 13-18 psi (9.1-1.26 kg/cm 2 ).
4. This test determines if the high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.

The fuel pump test terminal is located in the left rear corner of the engine compartment. When the engine is stopped, pump can be turned on by applying battery voltage (12 volts) to the test terminal.

Improper fuel system pressure can result in one of the following symptoms

1. Cranks, but won't run.
2. Code 44.
3. Code 55.
4. Cuts out, may feel like ignition problem.
5. Poor fuel economy, loss of power.
6. Hesitation.

Chart A7, Flow Chart - Fuel System Diagnosis. Scheme 53

CHART B1, RESTRICTED EXHAUST SYSTEM CHECK

1. With engine at operating temperature, connect a vacuum gauge to any convenient vacuum port on intake manifold. Increase engine speed to 1000 RPM and record vacuum reading.
2. Increase engine speed slowly to 2500 RPM. Note vacuum reading at steady RPM.
3. If vacuum at 2500 RPM decreases more than 3 in. Hg from reading at 1000 RPM, check complete exhaust system for collapsed pipe, heat distress and possible internal muffler failure.
4. If no faults are visible in exhaust system, remove exhaust pipe from engine and repeat steps 1) and 2). If vacuum still drops more than 3 in. Hg, check valve timing.

Code 13, Schematic - Open Oxygen Sensor Ckt. Scheme 54

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

1. Code 13 will set if the following conditions occur: Engine at normal operating temperature. At least one minute engine time after start. Oxygen signal voltage steady between .35-.55 volt. Throttle angle more than 7 percent. All conditions must be met for about 60 seconds. If conditions for a Code 13 exist, the system will not go into "closed loop".
2. This test determines if the oxygen sensor is the problem, or if the ECM and wiring are at fault.
3. When doing this test, use only a high impedence (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 (600 mV).

Normal "Scan" voltage varies between .1-1.0 volt (100-999 mV), while in "closed loop". Code 13 sets in one minute, if voltage remains between .35-.55 volt, but system will go into "open loop" in about 15 seconds.

Verify clean, tight ground connection for circuit No. 413. Open circuits No. 412 or 413 will result in a Code 13.

Code 13, Flow Chart - Open Oxygen Sensor Ckt. Scheme 55

Code 14, Flow Chart (1 of 2) - Coolant Sensor Temp Too High. Scheme 56

Code 14, Flow Chart (2 of 2) - Coolant Sensor Temp Too High. Scheme 57

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

1. Checks to see if code was set as result of hard failure or intermittent condition. Code 14 will set if the following conditions occur: Engine has been running for more than 10 seconds. Signal voltage indicates a coolant temperature greater than 275°F (135°C) for 3 seconds.
2. This test simulates conditions for a Code 15. If the ECM recognizes the open circuit (high voltage), and displays a low temperature, the ECM and wiring are okay.

The "Scan" tester reads engine temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 194°F (90°C), then stabilize when the thermostat opens.

If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperature may be checked using the "Scan" tester and should read close to each other.

When Code 14 is set, the ECM will turn on the engine cooling fan. A Code 14 will result if circuit No. 410 is shorted to ground.

Code 15, Fow Chart (1 of 2) - Coolant Sensor Temp Too Low. Scheme 58

Code 15, Fow Chart (2 of 2) - Coolant Sensor Temp Too Low. Scheme 59

1. Checks to see if code was set as a result of hard failure or intermittent condition. Code will set if engine has been running for more than 60 seconds. Signal voltage indicates a coolant temperature less than -35°F (-37°C).
2. This test simulates conditions for a Code 14. If the ECM recognizes the grounded circuit (low voltage), and displays a high temperature, the ECM and wiring are okay.
3. This test will determine if there is a wiring problem or a faulty ECM. If circuit No. 452 is open, there may also be a Code 21 stored.

After engine is started, the temperature should rise steadily to about 194°F (90°C), then stabilize when the thermostat opens. If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperature may be checked with a "Scan" tester and should read close to each other.

When a Code 15 is set, the ECM will turn on the engine cooling fan. A Code 15 will result if circuits No. 410 or 452 are open.

Code 21, Schematic - TPS Signal Volatge High. Scheme 60

1. This step checks to see if Code 21 is the result of a hard failure or an intermittent condition. A Code 21 will set if TPS reading is greater than 2.5 volts, engine speed is less than 1800 RPM, MAP reading is less than specification and all of the above conditions present for 2 seconds.
2. This step simulates conditions for a Code 22. If the ECM recognizes the change of state, the ECM and circuits No. 416 and 417 are okay.
3. This step isolates a faulty sensor, ECM, or an open circuit No. 452. If circuit No. 452 is open, there may also be a Code 15 stored.

A "Scan" tester displays throttle position in volts. Closed throttle voltage should be less than 1.25 volts. TPS voltage should increase at a steady rate as throttle is moved to WOT. A Code 21 will result if circuit No. 452 is open or circuit No. 417 is shorted to voltage.

Code 21, Flow Chart - TPS Signal Volatge High. Scheme 61

Code 22, Schematic - TPS Signal Voltage Low. Scheme 62

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

1. This test checks to see if Code 22 is the result of a hard failure or an intermittent condition. A Code 22 will set if the engine is running and TPS voltage is less than .2 volt (200 mV).
2. This test simulates conditions for a Code 21. If a Code 21 is set, or the "Scan" tester displays greater than 4 volts, the ECM and wiring are okay.
3. The "Scan" tester may not display 12 volts. The important thing is that the ECM recognizes the voltage as greater than 4 volts, indicating that circuit No. 417 and the ECM are okay.
4. If circuit No. 416 is shorted to ground, there may also be a stored Code 34.

A "Scan" tester displays throttle position in volts. Closed throttle voltage should be less than 1.25 volts. TPS voltage should increase at a steady rate as throttle is moved to WOT. An open ground at circuits No. 416 or 417 will result in a Code 22.

Code 22, Flow Chart - TPS Signal Voltage Low. Scheme 63

Code 23, Flow Chart - Manifold Air Temperature Too Low. Scheme 64

Code 23, Schematic - Manifold Air Temperature Too Low. Scheme 65

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

1. This test checks to see if Code 23 is the result of a hard failure or an intermittent condition. Code 23 will be displayed if the engine is running for longer than 2 minutes ("J" Body) or 8.5 minutes ("L" Body), signal voltage indicates a MAT temperature less than -22°F (-30°C) or there is no VSS signal.
2. This test simulates conditions for a Code 25. If the "Scan" tester displays a high temperature, the ECM and wiring are okay.
3. This test checks continuity of sensor wiring. If wiring is open there may also be a Code 21.

If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperature may be checked with the "Scan" tester and should read close to each other. A Code 23 will result if either sensor wire becomes open.

Code 24, Schematic - Vehicle Speed Sensor (VSS). Scheme 66

Vehicle speed information is provided to the ECM by the vehicle speed sensor Permanent Magnet (PM) generator mounted in the transaxle. The PM generator produces a pulsing voltage whenever vehicle speed is greater than 3 MPH. The A/C voltage level and the number of pulses increases with vehicle speed. The ECM then converts the pulsing voltage to MPH, which is used for calculations. MPH can be displayed with the "Scan" tester and should match speedometer reading.

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

1. Code 24 will set if vehicle speed equals zero MPH when the following conditions occur: Engine speed is between 1400 and 3600 RPM. Throttle angle is less than 2 percent. Low load condition, low MAP voltage, high manifold vacuum. Not in Park or Neutral. All conditions met for 5 seconds. These conditions are met during a road load deceleration. Disregard Code 24 that sets when drive wheels are not turning.
2. Circuits No. 400, 401 and 993 are okay if the speedometer works properly. Code 24 is being caused by a faulty ECM, faulty PROM or an incorrect PROM.

The "Scan" tester should indicate a vehicle speed whenever the drive wheels are turning more than 3 MPH. Check circuits No. 400 and 401 for proper connections. Make sure connections are clean and tight and the harness is routed correctly.

On vehicles with automatic transmissions, a faulty or misadjusted Park or Neutral safety switch can result in a false Code 24. Use the "Scan" tester and check for proper signal while in Drive. "Scan" reading should match speedometer.

Code 24, Flow Chart - Vehicle Speed Sensor (VSS). Scheme 67

Code 25, Flow Chart (1 of 2) - Manifold Air Temp Too High. Scheme 68

Code 25, Flow Chart (2 of 2) - Manifold Air Temp Too High. Scheme 69

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

1. This check determines if Code 25 is the result of a hard failure or an intermittent condition. A Code 25 will set if the following conditions occur: Engine has been running longer than 8 minutes. A MAT temperature is more than 275°F (135°C), detected for a time longer than 2 seconds. VSS signal is present.

If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperatures may be checked with the "Scan" tester and should read close to each other. A Code 25 will result if MAT sensor signal line is shorted to ground.

Code 32, Schematic - EGR System Error. Scheme 70

A properly operating EGR will directly affect the air/fuel mixture requirements of the engine. Since the exhaust gas introduced into the airflow is an inert gas (contains little or no oxygen), less fuel is required to maintain a correct air/fuel mixture. If the EGR system were to become inoperative, the inert exhaust gas would be replaced with oxygen and the air/fuel mixture would become leaner. This would be reflected in an increased block learn value.

The engine control cell of the 2.0L engine consists of 16 block learn cells. Since EGR is not used at idle, the closed throttle cell would not be affected by EGR system operation. The other block learn cells are affected by EGR operation and when the EGR system is operating properly, all block learn values in these cells should be close to the same. The difference between the closed throttle block learn cell and cell No. 10 is used by the ECM to monitor EGR system performance. When the difference between these 2 cells is greater than 12 and the block learn value in cell No. 10 is greater than 140, Code 32 is set. The system operates in block learn cell No. 10 during cruise conditions at approximately 55 MPH.

The Code 32 chart is a functional check of the EGR system. If the EGR system works properly, but a Code 32 has been set, check for other causes for an increased block learn value in cell No. 10.

1. Check for a blocked/restricted EGR passage.
2. Check the MAP sensor function. A MAP sensor may shift enough in calibration to affect the air/fuel mixture without setting a MAP related code.

Code 32, Flow Chart - EGR System Error. Scheme 71

Code 33, Schematic - MAP Sens Signal Voltage High. Scheme 72

Code 33, Flow Chart - MAP Sens Signal Voltage High. Scheme 73

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

1. This test will detemine if Code 33 is the result of a hard failure or an intermittent condition. A Code 33 will set if the following conditions occur: Engine is running. No VSS signal ("L" Body). MAP signal voltage is too high (low manifold vacuum). TPS less than 12 percent. These conditions occur for more than 5 seconds.
2. This step simulates conditions for a Code 34, if the ECM recognizes the change. The ECM and circuits No. 416 and 432 are okay.

With the ignition on, and engine stopped, the voltage chart may be used to determine the accuracy of the MAP sensor. This voltage reading is used by the ECM as a barometric pressure reading. A code 33 will result if the MAP ground circuit is open, or if the MAP signal circuit is shorted to voltage.

Code 34, Flow Chart (1 of 2) - MAP Sensor Signal Voltage Low. Scheme 74

Code 34, Flow Chart (2 of 2) - MAP Sensor Signal Voltage Low. Scheme 75

If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the Throttle Position Sensor (TPS) to control fuel delivery.

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

1. This test determines if Code 34 is the result of a hard failure or an intermittent condition. A Code 34 will set when the following conditions occur: MAP signal voltage is too low. The engine speed is greater than 1200 RPM. TPS signal greater than 15 percent
2. By jumping harness terminals "B" to "C", and with 5 volts to signal, this will determine if the sensor is at fault, or if there is a problem with the ECM or wiring.
3. The "Scan" tester may not display 12 volts. The important thing is that the ECM recognizes the voltage as more than 4 volts, indicating that the ECM and MAP signal circuit are okay.

With the ignition on and engine stopped, the voltage-to-altitude chart may be used to determine the accuracy of the MAP sensor. This voltage reading is used by the ECM as a barometric pressure reading.

A Code 34 will result if reference or signal circuits are open or shorted to ground.

Code 42, Schematic - Electronic Spark Timing (EST). Scheme 76

1. Code 42 indicates the ECM has seen an open or short in the EST or by-pass circuits. This test confirms Code 42 and that the fault is still present.
2. This test checks for a normal EST ground path through the ignition module. If circuit No. 423 is shorted to ground, reading will be less than 500 ohms.
3. As the test light voltage touches circuit No. 424, the module should "switch." This will cause the ohmmeter to "overrange" if the meter is in the 1000-2000 ohm position. A higher range will indicate more than 5000 ohms. This test ensures that the module "switched."
4. The module did not "switch". This step will test for a short in circuit No. 423, an open in circuit No. 424, and a faulty ignition module connection or module.
5. This test confirms that Code 42 is a faulty ECM and not an intermittent in circuits No. 423 and 424.

An open or ground in the EST circuit will result in the engine continuing to run, but in the ignition back-up mode (module timing). The "SERVICE ENGINE SOON" light will not remain on. If the fault is present next time the engine is started, a Code 42 will be stored in memory and vehicle will function in ignition back-up mode.

Code 42, Flow Chart - Electronic Spark Timing (EST). Scheme 77

Code 44, Schematic - Lean Exhaust Indication. Scheme 78

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

1. Code is 44 is set when oxygen sensor signal voltage on circuit No. 412 remains less than .3 volt for 50 seconds or more and system is operating in "closed loop".

Using the "Scan" tester, observe the block learn value at different RPMs. The "Scan" tester also displays the block cells, so that block learn values can be checked in each of the cells, to determine when Code 44 may have been set. If the conditions for Code 44 exist, the block learn values will be around 150.

1. Oxygen sensor wire or sensor pigtail may be mispositioned and contacting the exhaust manifold.
2. Check for ground in wire between connector and sensor.
3. Check for fuel contamination. Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injector. The water causes a lean exhaust signal at O2 sensor and can set a Code 44.
4. Fuel system will be lean if pressure is too low. It may be necessary to check fuel pressure while driving the vehicle at various speeds and/or loads to confirm problem.
5. If there is an exhaust leak, outside air can be pulled into the exhaust system and past the oxygen sensor. Vacuum or crankcase leaks can cause a lean condition.

Code 44, Flow Chart - Lean Exhaust Indication. Scheme 79

Code 45, Schematic - Rich Exhaust Indication. Scheme 80

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

1. Code 45 is set when the oxygen sensor signal voltage on circuit No. 412 remains greater than .7 volt for 30 seconds or more, system is in "closed loop", time after start is 30 seconds or more and throttle angle is not between 2 and 20 percent. Code 45, or rich exhaust can be caused if fuel pressure is too high. The ECM can compensate for some increase, however, if it gets too high, a Code 45 will be set.

Code 45, or rich exhaust, is most likely caused by one of the following

1. Fuel Pressure System will go rich if fuel pressure is too high. ECM can compensate for some increase using block learn, however, if pressure gets too high, a Code 45 will set. See CHART A7.
2. Leaking Injector Fuel system will go rich, if a fuel injector leaks. See CHART A7.
3. Open Ground Circuit If an open occurs in ground circuit No. 453, induced electrical "noise" may result, causing simulated reference pulses to be picked up by the ECM. The additional pulses result in a higher than actual engine speed signal. The ECM will increase injector pulse width ("on" time) to match the increased RPM signal. "Scan" tester will show higher than actual RPM, which can help in diagnosing this problem.
4. Canister Purge Check for fuel saturation. If full of fuel, check canister control and hoses.
5. MAP Sensor An output that causes the ECM to sense a higher than normal manifold pressure (low vacuum) can cause the system to go rich. Disconnecting the MAP sensor will allow the ECM to set a fixed value for the MAP sensor. If the rich condition is gone while the sensor is disconnected, substitute a different MAP sensor.
6. TPS An intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.
7. Oxygen Sensor Inspect oxygen sensor for silicone contamination from fuel, or use of improper RTV sealant. Sensor may have a White, powdery coating which will result in a high, but false signal voltage (rich exhaust indication). ECM will then reduce amount of fuel delivered to engine, causing a severe surge or driveability problem.
8. EGR Valve EGR sticking open at idle is usually accompanied by a rough idle and/or stalling.

Code 45, Flow Chart - Rich Exhaust Indication. Scheme 81

CODE 51, PROM/MEM-CAL FAILURE

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

Flow Chart C1A, (1 of 2)-Park/Neutral Switch (A/T Only). Scheme 82

Flow Chart C1A, (2 of 2)-Park/Neutral Switch (A/T Only). Scheme 83

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

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

1. Checks for a closed switch to ground with transmission in Park position. Different makes of "Scan" testers will display P/N status differently. Refer to tester manufacturer's operating manual for type of display used.
2. Checks for an open switch circuit in Drive.
3. Be sure "Scan" indicates Drive, even while wiggling shifter to test for an intermittent or misadjusted switch in Drive.

Chart C1D, Flow Chart (1 of 2) - Map Output Check. Scheme 84

Chart C1D, Flow Chart (2 of 2) - Map Output Check. Scheme 85

1. Checks MAP sensor output voltage to the ECM. This voltage, without engine running, represents a barometer reading to the ECM.
2. Applying 10 in. Hg (34 kPa) vacuum to the MAP sensor should cause the voltage to be 1.2-2.3 volts less than the voltage at test 1). When applying vacuum to the sensor, the change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.
3. Check vacuum hose to sensor for leaking air restriction. Be sure no other vacuum devices are on or connected to the MAP hose.

The power steering pressure switch is normally open to ground, and circuit No. 495 will be near battery voltage. Turning the steering wheel increases power steering oil pressure and its load on an idling engine. The pressure switch will close before the load can cause an idle problem. Closing the switch causes circuit No. 495 to read less than one volt and the ECM will increase the idle air rate and de-energize the A/C relay.

1. A pressure switch that will not close, or an open in circuits No. 495 or 450, may cause the engine to stop when power steering loads are high.
2. A switch that will not open, or a circuit No. 901 shorted to ground, may affect idle quality, and will cause the A/C relay to be de-energized.

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

1. Different makes of "Scan" testers may display the state of this switch in different ways. Refer to "Scan" tester operating manual to determine how this input is indicated.
2. Checks to determine if circuit No. 495 is shorted to ground.
3. This should simulate a closed switch.

Chart C1E, Schematic - Power Steering Switch "J" Body. Scheme 86

The power steering pressure switch is normally open to ground, and circuit No. 495 will be near battery voltage. Turning the steering wheel increases power steering oil pressure and its load on an idling engine. The pressure switch will close before the load can cause an idle problem. Closing the switch causes circuit No. 901 to read less than one volt and the ECM will increase the idle air rate and de-energize the A/C relay.

1. A pressure switch that will not close, or an open in circuits No. 495 or 450, may cause the engine to stop when power steering loads are high.
2. A switch that will not open, or a circuit No. 901 shorted to ground, may affect idle quanity, and will cause the A/C relay to be de-energized.

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

1. Different makes of "Scan" testers may display the state of this switch in different ways. Refer to "Scan" tester operating manual to determine how this input is indicated.
2. Checks to determine if circuit No. 901 is shorted to ground.
3. This should simulate a closed switch.

Chart C1E, Flow Chart - Power Steering Switch "J" Body. Scheme 87

Chart C1E, Schematic - Power Steering Switch "L" Body. Scheme 88

The power steering pressure switch is normally open to ground, and circuit No. 901 will be near battery voltage. Turning the steering wheel increases power steering oil pressure and its load on an idling engine. The pressure switch will close before the load can cause an idle problem. Closing the switch causes circuit No. 901 to read less than one volt and the ECM will increase the idle air rate and de-energize the A/C relay.

1. A pressure switch that will not close, or an open in circuits No. 901 or 450, may cause the engine to stop when power steering loads are high.
2. A switch that will not open, or a circuit No. 901 shorted to ground, may affect idle quanity, and will cause the A/C relay to be de-energized.

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

1. Different makes of "Scan" testers may display the state of this switch in different ways. Refer to "Scan" tester operating manual to determine how this input is indicated.
2. Checks to determine if circuit No. 901 is shorted to ground.
3. This should simulate a closed switch.

Chart C1E, Flow Chart - Power Steering Switch "L" Body. Scheme 89

Chart C2C Schematic, Idle Air Control "J" Body. Scheme 90

Chart C2C Schematic, Idle Air Control "L" Body. Scheme 91

C2C Flow Chart, Idle Air Control "L" Body. Scheme 92

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

1. Continue with test, even if engine will not idle. If idle speed is too low, "Scan" tester will display 90 or more counts, or steps. If idle is high, it will display zero counts. Occasionally an erratic or unstable idle may occur. Engine speed may vary 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 plunger retracted (more air) to a fixed "park" position for increased airflow and idle speed during the next engine start. A "Scan" tester will display 100 or more counts.
3. Be sure to disconnect the IAC valve prior to this test. The test light will confirm the ECM signals by a steady or flashing light on all circuits.
4. There is a remote possibility that one of the circuits is shorted to voltage, which would have been indicated by a steady light. Disconnect ECM and turn the ignition on. Probe terminals to check for this condition.

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

If idle is too high, stop engine. With ignition on, ground ALDL "test" terminal. Wait 45 seconds for IAC to seat, then, disconnect IAC. Unground "test" terminal and start engine. If idle speed is greater than 800 RPM, locate and correct vacuum leak. For other causes of improper idle, check the following

1. System Too Lean Idle speed may be too high or too low and engine speed varies up and down, DO NOT disconnect IAC. System may set Code 44.If "Scan" tester and/or a voltmeter reads an oxygen sensor output less than .3 volt (300 mV), check for low regulated fuel pressure or water in fuel. A lean exhaust, with an oxygen sensor output fixed above .8 volt (800 mV), will be a contaminated sensor. This may also set a Code 45.
2. System Too Rich If idle speed is too low, "Scan" tester counts are usually greater than 80. Fuel system is rich and may exhibit Black exhaust smoke. If "Scan" tester and/or voltmeter reads greater than .8 volt (800 mV), check for high fuel pressure or an injector that is leaking or sticking.
3. Throttle Body Remove IAC and inspect bore for foreign material or evidence of AC valve dragging bore.
4. PCV A faulty or incorrect PCV valve may result in an incorrect idle speed.
5. IAC Harness Connector IAC harness connector should be inspected carefully for proper contact.

Chart C4D-1, Schematic - DIS Misfire At Idle. Scheme 93

1. If the "misfire" complaint exists under load only, CHART C4D-2 must be used. 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 at the spark plug (25,000 volts).
3. If spark jumps the test gap after grounding the opposite plug wire, it indicates excessive resistance in the plug which was by-passed. A faulty or poor connection at that plug could also cause a misfire. Also check for carbon deposits inside the spark plug boot.
4. If carbon tracking is evident, replace coil and be sure plug wires relating to that coil are clean and tight. Excessive wire resistance or faulty connections could have caused the coil to be damaged.
5. If the no spark condition follows the suspected coil, that coil is faulty. Otherwise, the ignition module is the cause of no spark. This test could also be performed by substituting a known good coil for the one causing the no spark condition.

Chart C4D-1, Flow Chart - DIS Misfire At Idle. Scheme 94

Chart C4D-2, Schematic - DIS Misfire Under Load. Scheme 95

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

1. If the "misfire" complaint exists at idle only, use CHART C4D-1. Spark Tester (ST-125) must be used because it is essential to verify adequate available secondary voltage at the spark plug (25,000 volts). Spark should jump tester gap on all 4 plug wires.
2. If spark jumps the tester gap after grounding the opposite plug wire, it indicates excessive resistance in the plug which was by-passed. A faulty or poor connection at that plug could also result in the misfire condition. Also check for carbon deposits inside the spark plug boot.
3. If carbon tracking is evident, replace coil and be sure spark plug wire to that coil is clean and tight. Excessive wire resistance or faulty connections could have caused the coil to be damaged.
4. If the no spark condition follows the suspected coil, that coil is faulty. Otherwise, the ignition module is the cause of no spark. This test could also be performed by substituting a known good coil for the one causing the no spark condition.

Chart C4D-2, Flow Chart - DIS Misfire Under Load. Scheme 96

Chart C8A, Flow Chart (1 of 2) - Trans Converter Clutch. Scheme 97

Chart C8A, Flow Chart (2 of 2) - Trans Converter Clutch. Scheme 98

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

1. Light off confirms transmission 3rd gear apply switch is open.
2. At 30 MPH transmission/transaxle 3rd gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding ALDL "test" terminal with engine off should energize TCC solenoid by grounding circuit No. 422. This test checks capability of ECM to control solenoid.

A thermostat that is stuck in the open position, or opens at too low a temperature, may result in an inoperative TCC.

The shift light indicates best transmission shift point for maximum fuel economy. The light is controlled by ECM and is turned on by grounding circuit No. 456. The ECM uses coolant temperature, TPS, VSS, and RPM information for control. The ECM uses measured RPM and vehicle speed to calculate what gear vehicle is in. It is this calculation that determines when shift light should be turned on.

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

1. This should not turn on shift light. If light is on, there is a short to ground in circuit No. 456 wiring or a fault in ECM.
2. When ALDL "test" terminal is grounded, the ECM should ground circuit No. 456 and shift light should come on.
3. This checks shift light circuit up to ECM connector. If shift light illuminates, then ECM connector is faulty or ECM does not have ability to ground circuit.

Chart C8B, Flow Chart "J" Body - Manual Transaxle Shift Light. Scheme 99

Chart C8B, Flow Chart "L" Body - Manual Transaxle Shift Light. Scheme 100

A/C clutch operation is delayed by ECM for approximately .43 second after A/C is turned on. This allows the IAC to adjust RPM before the A/C clutch engages. The ECM will also disengage the A/C relay during Wide Open Throttle (WOT) operation, during power steering operation (high pressure), or if engine is overheating. When A/C pressure is greater than 40 psi (2.8 kg/cm 2 ), ECM will engage clutch relay by grounding circuit No. 459. At about 430 psi (30 kg/cm 2 ), the high pressure switch will open to disengage the A/C clutch and prevent system damage.

If complaint was insufficient cooling, the problem may be caused by an inoperative cooling fan or A/C pressure fan switch. Engine cooling fan should turn on when A/C pressure exceeds value to open switch. See CHART C12 to diagnose cooling fan.

Chart C10, Schematic - A/C Clutch Control "J" Body. Scheme 101

A/C Clutch operation is delay by ECM for aproximate .43 second after A/C is turned on. This allow the IAC to adjust RPM before the A?C clutch engages. The ECM will also disengage the A/C relay during Wide Open Thrttle (WOT) operation, during power steering opperation (high pressure), or if engine is overheating. When A/C pressure is greater than 40 psi (2.8 Kg/cm 2 ), ECM will engage clutch relay by grounding circuit No. 459. At about 430 psi (30 Kg/cm 2 ), the pressure switch will open to disengage the A/C clutch and prevent system damage.

If Complain was insufficient cooling, the problem may be caused by an inoperative cooling fan or A/C pressure fan switch. Engine cooling fan should turn on when A/C pressure exceeds value to open switch. See CHATR C12 to diagnose cooling fan.

Chart C10, Flow Chart - A/C Clutch Control "J" Body. Scheme 102

Chart C10, Schematic - A/C Clutch Control "L" Body. Scheme 103

When an A/C mode is selected on the A/C control switch, ignition voltage is supplied to the compressor low pressure switch. If there is sufficient A/C refrigerant charge, low pressure switch will close, completing the circuit to the closed high pressure cut-off switch. The voltage on circuit No. 366 to the ECM is shown by the "Scan" tester as an A/C request "ON" (voltage present) or "OFF" (no voltage) signal. When a request for A/C is seen by the ECM, ECM will ground circuit No. 459 of the A/C clutch control relay, the relay contact will close, and current will flow from circuit No. 366 to circuit No. 59 and engage the A/C compressor clutch. A "Scan" tester will show the grounding of circuit No. 459, as an A/C clutch "ON" signal. Also, when voltage is seen by the ECM on circuit No. 366, the cooling fan will be turned on.

The low pressure switch will be closed at 40-47 psi (2.8-3.3 kg/cm 2 ) and allow A/C clutch operation. At less than 37 psi (2.6 kg/cm 2 ), the low pressure switch will be open and the A/C clutch will not operate.

At about 430 psi (30 kg/cm 2 ), the high pressure switch will open to disengage the A/C clutch and prevent system damage.

Chart C10, Flow Chart - A/C Clutch Control "L" Body. Scheme 104

Chart C12, Schematic - Engine Cooling Fan "J" Body. Scheme 105

Battery voltage to operate the cooling fan motor is supplied to relay through fusible link in circuit No. 2. Ignition voltage to energize the relay is supplied to relay through alternator fuse in circuit No. 250. When the ECM grounds circuit No. 335, the relay is energized and the cooling fan is turned on. When the engine is running, the ECM will turn the cooling fan on if conditions for Code 14 or 15 exist or if the A/C system is on and coolant temperature is greater than 230°F (108°C).

If there's a complaint of an overheating problem, it must be determined if the complaint was due to an actual boilover, a failure in the temperature warning light, or if the temperature gauge indicates overheating.

If the temperature gauge or light indicates overheating, but no boilover is detected, the temperature gauge circuit should be checked. The gauge accuracy can also be checked by comparing the coolant sensor reading using a "Scan" tester and comparing its reading with the gauge reading.

If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not coming on, the coolant sensor has probably shifted out of calibration and should be replaced.

Chart C12, Flow Chart - Engine Cooling Fan "J" Body. Scheme 106

Chart C12, Schematic - Engine Cooling Fan "L" Body. Scheme 107

Battery voltage to operate the cooling fan motor is supplied to relay through fusible link in circuit No. 2. Ignition voltage to energize the relay is supplied to relay through fuse No. 9 in circuit No. 250. When the ECM grounds circuit No. 335, the relay is energized and the cooling fan is turned on. When the engine is running, the ECM will turn the cooling fan on if conditions for Code 14 or 15 exist or if the A/C system is on and coolant temperature is greater than 230°F (108°C).

If there's a complaint of an overheating problem, it must be determined if the complaint was due to an actual boilover, a failure in the temperature warning light, or if the temperature gauge indicates overheating.

If the temperature gauge or light indicates overheating, but no boilover is detected, the temperature gauge circuit should be checked. The gauge accuracy can also be checked by comparing the coolant sensor reading using a "Scan" tester and comparing its reading with the gauge reading.

If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not coming on, the coolant sensor has probably shifted out of calibration and should be replaced.

Chart C12, Flow Chart - Engine Cooling Fan "L" Body. Scheme 108

Throttle Body Injection CCC Wiring Diagram "J" Body. Scheme 109

Throttle Body Injection CCC Wiring Diagram "L" Body. Scheme 110