Reading and Clearing Diagnostic Trouble Codes

If a problem develops in a monitored system with the engine running, the "Check Engine" light will come "ON" and a trouble code will be stored in ECM memory. As long as a problem is present, the light will remain "ON" while the engine is running. If the problem is intermittent, the light will go out but a trouble code will be stored in ECM memory. As a bulb check, the "Check Engine" light will come "ON" with the ignition switched "ON" and the engine not running. If no codes are present, the light will go out upon starting the engine. If the light remains "ON," the system has detected a fault.

Refer to DIAGNOSTIC CIRCUIT CHECK for information on checking the function of the on-board diagnostic system.

ACCESSING TROUBLE CODES

"Check Engine" Light And Diagnostic Connector:

To access trouble codes, a test lead (white wire) and ground lead (black wire) are branched from the wiring harness under the center console near the ECM. With the ignition "ON" connect these two leads together. The "Check Engine" light will begin to flash code 12. Code 12 consists of one flash, a short pause, then two flashes. After a longer pause, code 12 will repeat two more times. This check indicates that the on-board diagnostic system is functioning. If no other codes are present, the cycle will repeat until the ignition is switched "OFF."

Reading Trouble Codes:

If trouble codes are stored in memory, the lowest number code will flash three times followed by the next higher code number until all stored codes have been displayed. The codes will then repeat in the same order until the test lead is disconnected. Code 14, for example, indicates a problem in the coolant sensor circuit.

CLEARING CODES FROM MEMORY

Fuse And ECM Harness Connections:

CAUTION: To avoid component damage, be sure ignition is "OFF" when disconnecting or reconnecting power to the ECM.

The trouble code memory receives a continuous 12 volts even with the ignition "OFF." After displaying and recording any trouble codes or after making repairs, the ECM memory should be cleared by interrupting the power for at least 10 seconds. This is accomplished by temporarily removing the #6 fuse in the engine compartment fuse and relay block or by disconnecting the battery. Codes are cleared automatically whenever the 14 pin ECM harness is disconnected. After clearing codes, it may be necessary to reset electronic accessories such as digital clocks and radios.

INTERMITTENT "CHECK ENGINE" LIGHT

"Intermittent" means that the "Check Engine" light comes on at times but does not stay on. Since codes may or may not be stored, the use of diagnostic charts could result in replacement of good parts.

Most intermittent problems are caused by faulty electrical wiring or connections. Carefully check these potential causes:

1. Poor mating of connector halves or terminals not fully seated in connector body.
2. Deformed or damaged terminals. All connector terminals in problem circuit should be carefully reformed to increase contact tension.
3. Poor terminal-to-wire connection. This requires removing terminal from connector body to properly check.
4. Poor ground connections.
5. If a visual check does not find the source of the problem, the vehicle may be driven with a voltmeter connected to a suspect circuit. An abnormal voltage reading when the problem occurs indicates the problem may be in that circuit.

An intermittent "Check Engine" light with no stored code may be caused by:

1. Arcing at ignition coil, plug wires or spark plugs.
2. Faulty power supply main relay.
3. Poor power supply circuit connections.
4. "Check Engine" light wire to ECM shorted to ground (circuit 22).
5. Diagnostic test lead to ECM shorted to ground (circuit 24).
6. Poor ECM ground connections at intake manifold.
7. Electrical system interference caused by a defective relay, ECM driven solenoid or switch. These problems cause an electrical surge and normally occur when the faulty component is operated.
8. Improper installation of accessories such as lights, sound systems, alarms, etc.

TROUBLE CODE IDENTIFICATION

CODE 12 Indicates that on-board diagnostics are functioning when diagnostic leads are connected and ignition is "ON" (engine not running). Code not stored in memory.

CODE 13 Oxygen sensor defective or open circuit.

CODE 14 Shorted coolant sensor circuit.

CODE 15 Open coolant sensor circuit.

CODE 21 Both idle and wide open throttle "ON" simultaneously in throttle valve switch.

CODE 22 Open or shorted starter signal circuit.

CODE 23 Shorted power transistor output terminal.

CODE 25 Open or shorted circuit for pressure regulator VSV.

CODE 26 Open or shorted circuit for canister VSV.

CODE 27 Open in ECM driver transistor for canister VSV.

CODE 32 EGR gas temperature sensor malfunction.

CODE 33 Open or shorted circuit in fuel injector harness, dropping resistor or inside ECM.

CODE 34 EGR gas temperature sensor or wiring faulty.

CODE 35 Ignition power transistor harness open circuit.

CODE 41 Crank angle sensor open circuit or faulty signal.

CODE 43 Throttle valve switch idle contact continuously "ON."

CODE 44 Lean signal from oxygen sensor.

CODE 45 Rich signal from oxygen sensor.

CODE 51 Abnormal ROM in ECM micro computer.

CODE 52 Abnormal RAM in ECM micro computer.

CODE 53 Open in ECM driver transistor for pressure regulator VSV.

CODE 54 Defective ignition power transistor or grounding system.

CODE 61 Shorted or broken air flow sensor hot wire.

CODE 62 Broken air flow sensor cold wire.

CODE 63 Open or shorted wiring or defective vehicle speed sensor.

CODE 64 Open in ECM driver transistor for fuel injectors.

CODE 65 Wide open throttle contact in throttle valve switch continually "ON."