Reading and Clearing Diagnostic Trouble Codes

***UPDATED BY TSB# ENG016, APRIL, 1989
NOTE: In the event of a recurring check engine light accompanied by an oxygen sensor fault code, the probable cause is a poor alternator to engine ground, and excessive resistance in the battery ground circuit. For the recommended correction refer to TSB# ENG016.

Diagnostic Connector Location:

Extracting fault codes.
1. Turn the ignition key `OFF'.
2. Connect the voltmeter to the self diagnosis connector.



NOTE: Do not disconnect the vehicle battery while the engine is running or while the ignition is on.

Diagnostic Trouble Codes 11 - 22:

Diagnostic Trouble Codes 23 - 43:

3. Turn the ignition key on and note the indication of the voltmeter. If the voltmeter indicates a steady 12 vdc the ECU has failed. If the voltmeter fluctuates, note the position and width of pulses and compare the pattern to the ECU codes chart to determine the error code.




NOTE: There may be more than one error code stored in the ECU memory. If so they will be displayed in ascending order with a 2 second pause between each code. Also, the oxygen sensor code is erased when the ignition is turned off. To test for oxygen sensor codes drive the vehicle a significant distance and check for diagnostic codes before turning the ignition off.



4. After the cause of a failure code has been detected and corrected the diagnostic code memory of the ECU should be cleared by disconnecting the vehicle battery for 15 seconds or more.