The ECM is a computer that can sense faults in the electronic engine control and store this fault information in its memory. This troubleshooting sequence describes how to get fault information from the ECM with a key in the ALDL and read the fault code from the Service Engine Soon light.
*****A dummy connector can be used to short terminals A and B in the diagnostic connector. *** If Terminal B is connected to Terminal A when the ignition switch is ON and the engine is stopped, all faults are indicated by a code (a sequence of illuminations) from the Service Engine Soon light.****
When the ignition switch is ON and the engine is stopped, the Service Engine Soon light will illuminate in a sequence to indicate a Code 12. A Code 12 is indicated by one long flash of light followed by a pause and then two short flashes to indicate that the fault monitor system is operating. A Code 12 only indicates that the fault monitor system is operating. The fault monitor system will repeat a Code 12 twice more and then send another code sequence if there is a fault. If there are no other fault codes stored in the ECM, a series of three Code 12 sequences continue to repeat as long as the SCAN Tool Tester or the dummy connector is plugged into the diagnostic connector and the ignition switch is turned to ON.
The code sequence occurs slowly at a rate of approximately one flash per second. Service people must wait long enough to make sure they have the complete and correct code sequences before beginning troubleshooting.