Description of On-Board Diagnostics

Electronic Control System
When the A/T control unit senses an abnormality in the input or output systems, the (D4) indicator light in the gauge assembly will blink. However, when the Service Check Connector (located under the dash on the passenger side) is connected with a jumper wire, the (D4) indicator light will blink the problem code when the ignition switch is turned on.





When the (D4) indicator light has been reported on, connect the two terminals of the Service Check Connector together. Then turn on the ignition switch and observe the (D4) indicator light.





Problem codes 1 through 9 are indicated by individual short blinks, Problem codes 10 through 16 are indicated by a series of long and short blinks. One long blink equals 10 short blinks. Add the long and short blinks together to determine the problem code. After determining the problem code, refer to the electrical system Symptom-to-Component Chart. DTC List - Transmission Control

Some PGM-FI problems will also make the (D4) indicator light come on. After repairing the PGM-FI system, disconnect the No. 39 BACK UP fuse (10 A) in the under-hood relay/fuse box for more than 10 seconds to reset the A/T control unit memory.

NOTE: Disconnecting the No. 39 BACK UP fuse also cancels the radio preset stations and the clock setting. Make note of the radio presets before removing the fuse so you can reset them.