Reading Self-Test Codes: Notes

Service codes are transmitted to Pin No. 4 (Self-Test Output) of SELF-TEST connector in the form of timed pulses. All service codes are 2 digit numbers which are generated one digit at a time. Codes are shown as voltage pulses (needle sweeps) on an analog Volt/Ohmmeter (VOM).

If a VOM is being used, pay careful attention to the length of the pauses in order to read the codes correctly. There will be a 2 second pause between each DIGIT in a code. There will be a 4 second pause between each CODE. The continuous memory codes are separated from the functional test service codes by a 6 second delay, a single 1/2 second sweep, and another 6 second delay. Always record the codes in the order received.

If a diagnostic tester is used, it will count the pulses and display them as a digital code. The STAR tester will add a zero (0) to single digit (Separator and Dynamic Response) codes. See CODE FORMAT DIAGRAMS. See Figure .

If the "CHECK ENGINE" light is used, numeric service codes will be displayed at the light.