MALFUNCTION INDICATOR LIGHT (MIL)
Vehicles are equipped with a Malfunction Indicator Light (MIL). As a bulb check, light will illuminate for approximately 5 seconds when ignition is on. MIL will also illuminate when a system failure is detected; a corresponding trouble code will set in Electronic Control Module (ECM) memory.
ECM is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, ECM will illuminate MIL (CHECK ENGINE light) on instrument panel. When malfunction is detected and light is turned on, a corresponding trouble code will be stored in ECM. To retrieve stored codes, see RETRIEVING CODES (NON-SCAN) or RETRIEVING CODES (SCAN TESTER). Malfunctions are recorded as hard failures or as intermittent failures.
Hard Failures
Hard failures cause Malfunction Indicator Light (MIL) to illuminate and remain on until problem is repaired. If light comes on and remains on during vehicle operation, retrieve code(s). See RETRIEVING CODES (NON-SCAN) table to determine cause of malfunction.
Intermittent Failures
Intermittent failures may cause malfunction light to flicker on and off after intermittent fault goes away. Corresponding trouble code will be retained in ECU memory. If related fault does not reoccur within a certain time frame, related trouble code may be erased from ECU memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article.
SERVICE PRECAUTIONS
Before proceeding with diagnosis, following precautions must be observed
- Ensure vehicle has a fully charged battery and functional charging system.
- Visually inspect connectors and circuit wiring being worked on.
- DO NOT disconnect battery or ECM. This will erase any fault codes stored in ECM.
- DO NOT cause short circuits when performing electrical tests. This will set additional fault codes, making diagnosis of original problem more difficult.
- DO NOT use a test light in place of a voltmeter.
- When checking for spark, ensure coil wire is NOT more than 1/4" from ground. If coil wire is more than 1/4" from ground, damage to vehicle electronics and/or ECM may result.
- DO NOT prolong testing of fuel injectors. Engine may hydrostatically (liquid) lock.
- When a vehicle has multiple fault codes, always repair lowest number fault code first.
RETRIEVING CODES (NON-SCAN)
- Before entering on-board diagnostics, refer to SERVICE PRECAUTIONS. Turn ignition switch to OFF position. Locate Data Link Connector (DLC), next to fuse block. Connect voltmeter positive lead to Data Link Connector (DLC) MFI diagnosis terminal and negative lead to ground terminal. (Scheme 12)
- Turn ignition switch to ON position. Voltmeter (analog) will display trouble codes by 12-volt pulses of voltmeter needle. Trouble codes are retrieved in numerical order. A constant repetition of short 12-volt pulses indicates system is normal. If system is abnormal, voltmeter will pulse between zero and 12 volts.
- Codes will appear on voltmeter as long and short 12-volt pulses. Long pulses represent tens; short pulses represent ones. For example: 4 long pulses and 3 short pulses indicate Code 43. After recording fault code(s), perform necessary repair(s) to indicated circuit(s). See FAULT CODES.
Scheme 12
RETRIEVING CODES (SCAN TESTER)
Note. If scan tester is needed to perform diagnostic test with key in START position, an auxiliary power source is needed to operate scan tester. Use optional Battery Harness (09391-33500 ).
Note. For specific operating procedures using scan tester, see instruction manual.
- Before entering on-board diagnostics, refer to SERVICE PRECAUTIONS. Turn ignition switch to OFF position. Locate Data Link Connector (DLC), next to fuse block. Connect power source terminal of scan tester to cigarette lighter socket. (Scheme 13)
- Connect scan tester to Data Link Connector (DLC). Turn ignition on. Read and record scan tester self-diagnostic output. Perform necessary repair(s). See FAULT CODES.
Scheme 13
CLEARING CODES
After testing and repairs have been completed, disconnect negative battery cable for at least 15 seconds to clear codes.
ECM POWER & GROUND CIRCUITS
See SYS/COMP TESTS article.
FAULT CODES
Note. Codes listed in FAULT CODES table are not used on all vehicles. For testing procedures, see DIAGNOSTIC TESTS.
Note. If MIL stays on, ECM may be faulty.
| Code | Description | Possible Cause |
|---|---|---|
| 11 | Heated Oxygen Sensor (HO2S) Malfunction | Faulty HO2S, Connector Or Harness, Incorrect Fuel Pressure, Defective Injector(s), Or Intake Air Leaks |
| 12 | Airflow Sensor Malfunction | Faulty Airflow Sensor, Connector, Or Harness |
| 13 | Intake Air Temperature (IAT) Sensor Malfunction | Faulty IAT Sensor, Connector, Or Harness |
| 14 | Throttle Position (TP) Sensor Malfunction | Faulty TP Sensor, Connector, Wiring, Or TP Switch |
| 15 | Idle Speed Control (ISC) Motor Position Sensor Malfunction | Faulty ISC Motor Position Sensor Or Faulty Throttle Position Sensor, Connector, Or Harness |
| 21 | Coolant Temperature Sensor (CTS) Malfunction | Faulty CTS, Connector, Or Harness |
| 22 | Crankshaft Position (CKP) Sensor Malfunction | Faulty Distributor (If Equipped) Or Faulty CKP Sensor, Connector, Or Harness |
| 23 | Top Dead Center (TDC) Sensor Malfunction | Faulty TDC Sensor, Connector, Or Harness |
| 24 | Vehicle Speed Sensor (VSS) Malfunction | Faulty VSS, Connector, Or Harness |
| 25 | Barometric Pressure (BARO) Sensor Malfunction | Faulty BARO Pressure Sensor, Connector, Or Harness |
| 41 | Fuel Injector Malfunction | Low Or High Injector Coil Resistance, Connector, Or Harness |
| 42 | Fuel Pump Malfunction | Faulty ECM Or Faulty MFI Relay Connector Or Harness |
| 43 | EGR Temperature Sensor Malfunction | Faulty EGR Valve, EGR Temperature Sensor, EGR Solenoid, Or EGR Vacuum Control Connector Or Harness |
| 44 | Ignition Coil/Power Transistor Malfunction | Faulty Ignition Coil Or Faulty Ignition Power Transistor Unit Connector Or Harness |
| 59 | Heated Oxygen Sensor (HO2S) Malfunction | Faulty HO2S, Connector Or Harness, Incorrect Fuel Pressure, Defective Injector(s), Or Intake Air Leaks |
FAULT CODES
CODE 11 & 59 - HEATED OXYGEN SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Scan Tester Procedure
Access scan tester service data item No. 11. Tester should display sensor voltage. Ensure engine is at normal operating temperature. See HO2S OPERATING VOLTAGE SPECIFICATIONS table.
| Engine RPM | Output (Volts) |
|---|---|
| 750 | .4 Or Less |
| 2000 | .6-1.0 |
| 4000 To 750 (1) | .2 Or Less |
| 750 To 4000 (2) | .6-1.0 |
| (1) Sudden deceleration. (2) Sudden acceleration. | |
| (1) | Sudden deceleration. |
| (2) | Sudden acceleration. |
HO2S OPERATING VOLTAGE SPECIFICATIONS
CODE 12 - AIRFLOW SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Access airflow sensor service data item No. 12. Tester should display sensor air volume measured in hertz (Hz). Ensure engine is at normal operating temperature with all accessories off. Transmission should be in Neutral or Park with steering straight ahead. Frequency should be 27-33 Hz at 750 RPM and 60-80 Hz at 2000 RPM.
CODE 13 - INTAKE AIR TEMPERATURE SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Access intake air temperature sensor service data item No. 13. Scan tester should display sensor temperature. Start and run engine. Sensor temperature should match outside ambient temperature.
CODE 14 - THROTTLE POSITION SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Access TPS service data item No. 14. Scan tester should display sensor voltage. Turn ignition on. At idle position, sensor voltage should be .45-.55 volt. Voltage should increase with throttle opening. Voltage at WOT should be 4.5-5.5 volts.
CODE 15 - IDLE SPEED CONTROL MOTOR POSITION SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
- Access ISC motor position sensor service data item No. 15. Tester should display sensor motor voltage. Ensure engine is at normal operating temperature with all accessories off. Transmission should be in Neutral or Park with steering straight ahead.
- Voltage should be .5-1.3 volts with A/C off and .8-1.8 volts with A/C on. Continue with A/C on. Shift transmission into Drive. Ensure parking brake is set. Voltage should be .9-1.9 volts.
CODE 21 - COOLANT TEMPERATURE SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Access Coolant Temperature Sensor (CTS) service data item No. 21. Scan tester should display sensor temperature with engine running. As engine temperature increases, monitor scan tester readings while measuring actual engine coolant temperature with thermometer. Scan tester readings should match thermometer readings.
CODE 22 - CRANKSHAFT POSITION SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Access CKP service data item No. 22. Scan tester should display idle speed. See CKP IDLE SPEED SPECIFICATION table.
| Coolant Temperature °F (°C) | Engine RPM |
|---|---|
| 4 (-20) | 1500-1700 |
| 32 (0) | 1350-1550 |
| 68 (20) | 1200-1400 |
| 104 (40) | 1000-1200 |
| 176 (80) | 650-850 |
CKP IDLE SPEED SPECIFICATION
CODE 23 - TOP DEAD CENTER SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Manufacturer does not provide testing information. See tester instruction manual for testing procedures.
CODE 24 - VEHICLE SPEED SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Manufacturer does not provide testing information. See tester instruction manual for testing procedures.
CODE 25 - BAROMETRIC PRESSURE SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Access scan tester service data item No. 25. With ignition on, scan tester should display 760 mm Hg at sea level. Other test specification readings are; 710 mm Hg at 1969 ft. (600 m), 660 mm Hg at 3937 ft. (1200 m) and 610 mm Hg at 5906 ft. (1800 m).
CODE 41 - FUEL INJECTOR FAILURE
Note. Ensure engine compression is within specification. See SPECIFICATIONS article. Ensure ignition system is operating properly. Low compression or ignition system breakdown can affect fuel injector performance.
Note. If after all testing procedures have been completed, fuel injection system is still inoperative, substitute ECM with known good unit and retest.
- Access fuel injector service data item No. 41. Scan tester should display injector drive time. Ensure engine is at normal operating temperature. Turn all accessories off. Ensure shift selector is in Park or Neutral.
- Inspect fuel injector drive times with engine cranking and running. See FUEL INJECTOR DRIVE TIME table. FUEL INJECTOR DRIVE TIME Coolant Temp. °F (°C) Engine RPM Drive Time (ms) Engine Cranking 32 (0) Less than 250 18 68 (20) Less than 250 34 176 (80) Less than 250 6.1 Engine Running 176 (80) 750 2.5-3.1 176 (80) 2000 2.2-2.8
- Access injector actuator test. Select items 01 through 04 for injectors No. 1 through No. 4. Check decrease in engine idle speed when each injector is disabled to confirm injector operation.
CODE 42 - FUEL PUMP FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Access scan tester service data item No. 7. While cranking engine, check fuel return hose for pulsation, indicating fuel flow. Remove filler cap and listen for pump operating sound. Fuel pump is located inside fuel tank.
CODE 43 - EGR TEMPERATURE SENSOR FAILURE
Note. If after all testing procedures have been completed, system is still inoperative, substitute ECM with known good unit and retest.
Connect tachometer and scan tester to vehicle. Access EGR temperature sensor service data item No. 43. Tester should display sensor temperature. With engine at normal operating temperature and idling at 750 RPM for at least 2 minutes, check sensor temperature. Scan tester should display 158°F (70°C) or less. Accelerate engine to 3500 RPM. Scan tester should display 158°F (70°C) or more.
CODE 44 - IGNITION COIL/POWER TRANSISTOR FAILURE
Note. If after all testing procedures are completed, system is still inoperative, substitute ECM with known good unit and retest. Manufacturer does not provide scan tester test information.
Manufacturer does not provide testing information. See tester instruction manual for testing procedures.
SUMMARY
If no hard fault codes (or only pass codes) are present, driveability symptoms exist, or intermittent codes exist, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.