Reading Diagnostic Trouble Codes

Fig. 3 Location Of ECM & Fuse Box:

Fig. 5 Initial Diagnostic Circuit Check:

Trouble codes may be accessed by installing a spare fuse into the diagnostic terminals of the fuse box and turning the ignition switch to the On position, refer to Figs. 3 and 5.

Fig. 3 Location Of ECM & Fuse Box:

The Electronic Control Module (ECM) monitors vehicle operation by the use of sensors. The sensors output is compared to parameters set in the ECM memory. If these parameters are exceeded, the self-diagnosis system in the ECM detects system failure and identifies the circuit at fault by use of trouble codes. The ECM is located behind lefthand side of the instrument panel, Fig. 3.

Fig. 4 Trouble Code Identification:

The Check Engine lamp, located on the instrument panel, displays the trouble codes. In normal operation the lamp will illuminate when the ignition switch is turned On. However, when the engine is started two different lamp functions can occur. The Check Engine lamp may turn Off immediately, indicating there is no fault at that time. The Check Engine lamp may stay illuminated for at least ten seconds, informing the vehicle operator there is a system failure, and store a trouble code in the ECM memory. In some cases the lamp will continue to stay illuminated until vehicle service has been performed. When a trouble code is accessed from the ECM memory the Check Engine lamp will flash in a series indicating the trouble code number, Fig. 4. When multiple system failures occur applicable codes will be indicated three times each. Codes will continue to flash as long as the ignition switch is On, and the spare fuse is installed in the diagnostic connector, or the jumper wire is installed in the underhood diagnostic terminal.

Prior to accessing trouble codes from the ECM, never disconnect the battery cable, ECM connectors, ECM ground wire harness from engine, or 15 amp fuse from the tail light circuit. Disconnecting any of these circuits will cause the ECM memory to be erased.

When performing test procedures, cooling of the oxygen sensor during engine idle will cause the system to return to ``Open Loop'' operation. To return to a ``Closed Loop'' mode, run the engine at part throttle for a minimum of two minutes.