Questions and Answers
Cavalier OBD Codes
Q. I have a 1994 Cavalier Wagon with a 2.2 litre engine. How can I tell if the on board computer is the new OBD-II? Also when trying to access a trouble code through the ALDL plug the check engine soon light stayed on but did not flash any codes not even the code 12.
If My car has the new OBD-II system do I have to access the trouble codes in a different way? Hope you can help.
Thanks,
EdA. OBD-II was not incorporated until the 1995 model year. 1994 and earlier cars used what was called OBD-I and each car maker had their own coding system. OBD-II was adopted to standardize Diagnostic Trouble Codes (DTC).
To extract a trouble code from the computer for diagnostic purposes, the Assembly Line Communication Link (ALDL) connector is used.
ALDL Connector (Located Underdash)The ALDL diagnostic connector is located in the passenger compartment. Terminal B of the connector is the test terminal and terminal A is the ground used for diagnostic display.
If the test terminal is grounded with the ignition "ON" and engine not running, the system will enter the diagnostic mode. In this mode, the computer will display a Code 12, three consecutive times, by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" or light. A Code 12 consists of one flash, a short pause, then two flashes in rapid succession. After Code 12 is displayed, any stored trouble codes will be displayed by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" light. All codes are displayed 3 times each then a code 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids. After determining the trouble code(s), see trouble code description.
If you are not getting any DTC's at all, then the problem is most likely a defective EPROM. Replace the EPROM only after trying a known good PCM. If you get codes with the known good PCM, then you will need to replace the EPROM or PCM.
Additional Information provided courtesy of ALLDATA
