Reading Self-Test Codes: Notes

WARNING: This page is about a different car, the 1987 Mercury Topaz and 1987 Ford Tempo. However, it is still accessible from the selected car via links, so may be relevant.

Service codes are transmitted to Pin No. 4 (Self-Test Output) of SELF-TEST connector in the form of timed pulses. All 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, careful attention to the length of the pauses is necessary 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.

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.