Notes on Displaying Fault Codes - Start Here

Beginning in 1989, all models sold in California, and some models sold in other states and Canada are equipped with a fault indicator lamp located on the instrument panel. The fault lamp is a means of notifying the operator of problems with the ECU or related circuits and devices. If an ECU related circuit malfunctions while the engine is running, the fault lamp will illuminate. This will notify the driver that a problem has been detected, and a trouble code will be stored in the computer memory. On most models, if the trouble is intermittent the lamp will turn off when the problem is no longer present, but a trouble code will still be stored. On other models, when a problem is detected the lamp will light and stay lit until the fault memory is erased, even if the problem was intermittent.

Under normal conditions, the fault lamp will illuminate when the key is turned ON, and will go out when the engine is started. This is a bulb check and indicates that the self diagnostic warning circuit is functioning. If the vehicle is equipped with a fault lamp, and the lamp does not illuminate when the key is turned ON, or does not go out when the engine is started then a malfunction is present, and the system should be inspected.

Typical Fault Indicator Light:

To verify that the vehicle is equipped with a functional fault lamp turn the ignition "on", and observe dash lights. A "CHECK" light with an engine symbol should illuminate (fault indicator lamp). If no fault lamp is showing, leave the ignition turned "on" and insert a fuse into the top of the fuel pump relay (located in the fuse/relay panel under the hood and just front of the lower left corner of the windshield, in the plenum).

Fuse/Relay Panel Showing Fuel Pump Relay w/Fuse Receptacle:

If the vehicle is equipped with a functional fault lamp, the lamp will light up while the fuse is inserted, or while test connectors under dash are properly bridged (see DISPLAYING FAULT CODES in this section), and provided the lamp is not burned out. If the lamp did not light when the ignition was turned on, but did light with a fuse inserted in the fuel pump relay, then there may be a problem with the ECU lamp driver circuit, ECU terminal connection/wiring, or the ECU itself. Before suspecting a bad ECU, or if at this point no fault lamp has shown, follow procedures under DISPLAYING FAULT CODES for MODELS WITHOUT FAULT LAMP.

The fault lamp is also used to display any trouble codes that have been stored in memory, however, some models equipped with a fault lamp will not display codes by flashing the lamp. These models require connecting an LED test light to special test connectors on the wiring harness to display codes (see DISPLAYING FAULT CODES in this section). Codes are read by counting the number of flashes of the lamp while the computer is in diagnostic mode. For the procedure for entering diagnostic mode and displaying fault codes, as well as a list of the codes and their definitions, see DISPLAYING FAULT CODES and EXPLANATION OF FAULT CODES in this section.