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

Diagnostic Connectors:

"Check Engine" Light:

To access trouble codes, a test lead (white wire) and ground lead (black wire) are branched from the wiring harness 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.

Faults indicated by codes 13, 31, 44 and 45 require engine operation at part throttle for up to five minutes after engine warm-up before the "Check Engine" light will come on and store a code. Code 15 takes five minutes of engine operation before it will display. Disconnect the test leads before starting the engine.

CLEARING CODES FROM MEMORY

Main Fuse:

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 #3 fuse (instrument panel fuse box) or the main fuse (engine compartment fuse and relay block) or by disconnecting the battery. After clearing codes, it may be necessary to reset electronic accessories such as digital clocks and radios.

INTERMITTENT "CHECK ENGINE" LIGHT, NO STORED CODES

These conditions will cause an intermittent "Check Engine" light without storing trouble codes:

1. If engine speed drops below 200rpm for any reason, the light will come on until rpm exceeds 200 and for four seconds thereafter.

2. Low battery voltage (under 9V) at ECM.

3. Loss of trouble code memory. Momentarily grounding the dwell lead with engine at idle should store code 23. After engine is stopped and ignition turned "ON," check for voltage at ECM terminal "C46-1" and for code 23. If voltage is present but no code is stored, ECM is defective.

4. Check for intermittent connections in these circuits:
a. Ignition coil to ECM terminal "C46-10"
b. Battery to ECM terminal "C46-1"
c. ECM terminal "C46-13" to engine ground
d. ECM terminal "C46-4" to lamp driver
e. ECM terminal "C46-3" to battery (including ECM relay circuit)

TROUBLE CODE IDENTIFICATION

CODE 12 No ignition reference pulses to ECM. This code is not stored in memory and will only flash while the fault is present. It is displayed before the engine is started.

CODE 13 Oxygen sensor circuit. The engine must run 1 minute at part throttle, under road load, before this code will set. The code will not set when the coolant temperature is below 70°C (158°F) and/or the time since engine start has exceeded 2 minutes.

CODE 14 Shorted coolant sensor circuit. The engine must run 2 minutes before this code will set.

CODE 15 Open coolant sensor circuit. The engine must run 5 minutes before this code will set.

CODE 21 Idle switch and MAP sensor failure. This code will set if either condition 1, 2 or 3 exist.
1. Vehicle speed is 0 km/h and engine speed is between 200 and 1000 rpm. MAP sensor output voltage is more than 500 mmHg absolute as input signal for 5 seconds.
2. Idle switch "OFF." Map sensor output voltage is less than 100 mmHg absolute as input signal for 5 seconds.
3. MAP sensor output voltage is between 400 and 450 mmHg absolute as input signal and engine speed is more than 1500 rpm. Idle switch is "ON" for more than 5 seconds.

CODE 22 Fuel cut solenoid circuit open or grounded. The engine must run under decelerating condition at over 2000 rpm before this code will set.

CODE 23 Duty solenoid circuit open or grounded.

CODE 25 AIR VSV circuit open or grounded.

CODE 26 Canister VSV circuit open or grounded.

CODE 27 Constant high voltage from VSV to ECM.

CODE 31 No ignition reference pulses to the ECM after 10 seconds at part throttle, under load. This code will store in memory.

CODE 32 EGR system failure and sensor circuit failure.

CODE 34 EGR gas sensor circuit failure.

CODE 44 Fuel metering lean. This code will set when the following four conditions exist simultaneously:
1. Coolant temperature above 70°C (158°F).
2. Throttle is partially open.
3. Vehicle speed is either 0 km/h or between 20 and 80 km/h.
4. More than 5 seconds have elapsed since fuel cut cancel.

Code 44 will not set if either of these conditions exist:
1. Barometric map (MAP sensor output voltage) is below 596 mmHg absolute.
2. Code 13 or 21 are stored in memory or coolant temperature is above 150°C (302°F).

CODE 45 Fuel metering rich. This code will not set when the ECM judges a high altitude condition (above 2500m/8000ft). This code will set when the following five conditions exist simultaneously:
1. Coolant temperature above 70°C (158°F).
2. Throttle is partially open.
3. Engine speed is less than 2500 rpm.
4. Vehicle speed is either 0 km/h or between 20 and 80 km/h.
5. More than 30 seconds have elapsed since initiating canister purge.

Code 45 will not set if either of these conditions exist:
1. Barometric map (MAP sensor output voltage) is below 596 mmHg absolute.
2. Code 13 or 21 are stored in memory or coolant temperature is above 150°C (302°F).


CODE 51 Shorted fuel cut solenoid circuit and/or faulty ECM.

CODE 52 Faulty RAM in ECM.

CODE 53 Shorted AIR VSV and/or faulty ECM.

CODE 54 Shorted vacuum control solenoid and/or faulty ECM.

CODE 55 Faulty A/D converter in ECM.