Data Link Connector

ALDL Connector:

PROCEDURE:

Turn the ignition to the "ON" or "RUN" position (engine off). Make a note of the "SERVICE ENGINE SOON" light. Light should come on steady. If there is no light or the light flashes, Related Tests, Information and Procedures and do not proceed with remainder of test. Results of test will be invalid.
Turn the key on to the "RUN" position (engine off). Ground the diagnostic terminal (ALDL terminal A to B). The "SERVICE ENGINE SOON" ("CHECK ENGINE") light should flash a code 12. This is displayed, on the CHECK ENGINE light, by 1 flash followed by a short pause then 2 flashes. This should repeat 3 times. A code 12 should always flash when an on-board diagnostic check is performed. Any other codes, stored in the computer (ECM), will follow a code 12. If any other codes are stored, or code 12 does not flash, or the CHECK ENGINE light is on steady, or not at all, refer to Computers and Control Systems.

CLEARING TROUBLE CODES:


CAUTION: To prevent major damage to the ECM, the key must be in the OFF position any time ECM power is disconnected or reconnected. This applies to not only trouble code clearing, but also when removing a battery cable for component repair or replacement and testing procedures.

PROCEDURE:

To clear the trouble codes from the memory of the ECM, either to determine if the malfunction will occur again or because a repair has been completed, the ECM power feed must be disconnected for at least thirty (30) seconds. Depending on how the vehicle is equipped, the ECM power feed can be disconnected at the positive battery terminal pigtail, the in-line fuse holder that originates at the positive connection at the battery, or the ECM fuse in the fuse block. The negative battery terminal may be disconnected, but other on-board memory data, such as pre-set radio tuning, will also be lost.

When using a hand held diagnostic scanner, or scan tool to read codes, clearing the diagnostic trouble codes is done in the same manner as in the above procedure.


After the computer memory has been cleared, a change may be noted in vehicle performance. To restore normal vehicle performance, drive with engine at normal operating temperature, with the accelerator pedal going through idle, part throttle, and moderate acceleration modes until normal performance is restored.