System Diagnosis: Notes

The engine control system is equipped with a self-diagnostic capacity. When a failure occurs within the system, a trouble code is stored in ECU memory.

To recall trouble codes, install a test bulb (No. 1982 or equivelant) between under hood diagnostic connector pin 2 and pin 4 of the D2 connector. Push the WOT switch lever on the throttle body to closed position and close the ISC motor plunger. This activates the closed throttle switch. Have an assistant turn ignition switch to the "ON" position while you observe the test bulb.

The test bulb will light for a moment, then go out. This should always occur, regardless of whether or not any trouble codes are stored, to indicate that the ECU is functional.

The bulb will then indicate all stored trouble codes (maximum of 2) as a series of brief flashes (flash, flash for code 2; flash, flash, flash, for code 3, etc.). If 2 trouble codes are stored in ECU memory, the first code stored is indicated first, followed by a short pause, and the most recent code is indicated. After a longer pause, the cycle repeats. Each trouble code indicates the malfunction of a specific sensor or sensors. Note codes.

Some injection system difficulties or abnormalities may occur without setting a trouble code. If this happens, refer to specific problem descriptions listed after trouble code references.