SYSTEM DIAGNOSIS
System diagnosis can be accomplished using an appropriate scan tester, a voltmeter or the Malfunction Indicator Light (MIL). See RETRIEVING CODES . Engine Control Module (ECM) monitors several different engine control system circuits. If an abnormal input signal occurs, a trouble code is stored in ECM memory and assigned a trouble code number. Each circuit has its own trouble code number and message. A specific trouble code indicates a particular system failure, but does not indicate that cause of failure is necessarily within system.
A trouble code does not condemn any specific component; it simply points out a probable malfunctioning area. If a trouble code is set, ECM will turn on MIL. System malfunctions encountered are identified as either hard failures or intermittent failures as determined by ECM.
TROUBLE CODES
Note. Codes listed in TROUBLE CODE INDEX table are not used on all vehicles.
Note. If MIL stays on, ECM may be faulty.
| Code | Description | Possible Cause |
|---|---|---|
| 11 | Heated Oxygen Sensor (HO2S) (4-Wire Oxygen Sensor) | Faulty O2S, Connector Or Harness, Low Or High Fuel Pressure, Defective Injector(s), Intake Air Leaks |
| 12 | Airflow Sensor | Faulty Airflow Sensor, Connector Or Harness |
| 13 | Intake Air Temperature Sensor | Faulty IAT Sensor, Connector Or Harness |
| 14 | Throttle Position Sensor | Faulty TP Sensor, Connector Or Harness, Closed Throttle Position Switch |
| 21 | Engine Coolant Temperature (ECT) Sensor | Faulty ECT Sensor, Connector Or Harness |
| 22 | Crankshaft Position (CKP) Sensor | Faulty Distributor Assembly (If Equipped), Faulty CKP Sensor, Connector Or Harness |
| 23 | Camshaft Position Sensor | Faulty Distributor Assembly (If Equipped), Faulty CMP Sensor, Connector Or Harness |
| 24 | Vehicle Speed Sensor | Faulty VSS, Connector Or Harness |
| 25 | Barometric Pressure Sensor | Faulty BARO Pressure Sensor, Connector Or Harness |
| 31 | Knock Sensor | Faulty Knock Sensor, Connector Or Harness |
| 36 | Ignition Timing Adjustment Signal | Connector Or Harness |
| 41 | Fuel Injector | Low Or High Injector Coil Resistance, Connector Or Harness |
| 43 | EGR Temperature Sensor | Faulty EGR Valve, Faulty EGR Temperature Sensor, Faulty EGR Solenoid, Faulty EGR Vacuum Control, Connector Or Harness |
| 44 | Ignition Coils | Faulty Ignition Coil, Faulty Ignition Power Transistor Unit, Connector Or Harness |
| 52 | Ignition Coils | Faulty Ignition Coil, Faulty Ignition Power Transistor Unit, Connector Or Harness |
| 53 | Ignition Coils | Faulty Ignition Coil, Faulty Ignition Power Transistor Unit, Connector Or Harness |
| 55 | Idle Air Control (IAC) Position Sensor | Faulty IAC Position Sensor, Faulty ECM, Connector Or Harness |
| 59 | Rear Oxygen Sensor (O2S) | Faulty O2S Sensor, Faulty O2S Sensor Heater, Faulty ECM, Connector Or Harness |
| 69 | Rear Oxygen Sensor (O2S) | Faulty O2S Sensor, Faulty O2S Sensor Heater, Faulty ECM, Connector Or Harness |
TROUBLE CODE INDEX
DIAGNOSTIC TESTS
| CAUTION | Ensure ignition switch is in OFF position when performing resistance tests. |
Note. Perform all resistance and voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm impedance, unless stated otherwise in test procedures.
Note. For wire color identification at ECM terminals, see appropriate pin voltage chart in PIN VOLTAGE CHARTS article in the ENGINE PERFORMANCE Section.
Clear trouble codes after each repair. See CLEARING CODES under SELF-DIAGNOSTIC SYSTEM. Recheck for codes to confirm repair. See RETRIEVING CODES under SELF-DIAGNOSTIC SYSTEM.