Reading Diagnostic Trouble Codes

Diagnostic Connector Identification:

DIAGNOSTIC CODE INTERPRETATION
The Electronic Control Module (ECM) monitors operation of the emission control system. Some components are monitored continuously, others only during specified operating conditions. When the ECM detects a malfunction lasting longer than a specified period of time the ECM will generate a trouble code that can be read at the diagnostic connector.

- There are fourteen diagnostic items (including normal operation) that will generate diagnostic codes.

- The trouble codes are erased when the vehicle battery is disconnected for more than ten seconds.

NOTE: If the oxygen sensor is disconnected during engine operation for testing purposes a code will be stored and must be cleared after the test is complete.

To test for oxygen sensor codes drive the vehicle a significant distance and check for diagnostic codes before turning the ignition off. Do not however disconnect the battery with the ignition ON or the engine running as permanent damage to the vehicle electronic components may result.

If multiple codes have been set, the codes will be sent sequentially, in ascending order, with a 2 second pause between codes.

Diagnostic Connector:

READING DIAGNOSTIC CODES
1. Connect an analog voltmeter to the ground and self diagnosis output pin of the diagnostic connector.
2. Set the ignition switch to "ON", the voltmeter needle will deflect for a particular duration and a certain number of times.

EXAMPLES:
Code 13
- The needle will deflect one time for approximately 0.5 second. This will represent one module of ten. There will be approximately a one second delay and then the needle will deflect three times for approximately 0.2 seconds with 0.1 second delay between deflections. This will represent three modules of one.

Code 23
- The needle will deflect two times for approximately 0.5 second with approximately 0.3 second delay between deflections. This will represent two modules of ten. There will be approximately a one second delay and then the needle will deflect three times for approximately 0.2 seconds with 0.1 second delay between deflections. This will represent three modules of one.

3. Note the pattern of pulses displayed on the voltmeter. If the voltmeter indicates a steady 12 Volts DC, the ECM has failed.
4. Refer to the Trouble Code to Fault Message Chart to determine which circuit is outside of the acceptable parameters.
5. Test and repair the cause as necessary.
6. Clear the trouble codes by disconnecting the vehicle battery negative terminal for 16 seconds or longer.
7. Road test the vehicle and check for new codes that may have been set.