Entering Diagnostic Mode
The ECU will store faults for self-diagnosis. The ECM has a permanent fault code memory (50 states and Calif.), as well as a temporary fault code memory (Calif. only). When ECU detects a temporary fault, the "FAULT INDICATOR LIGHT" (FIL) on the instrument panel will flash. The FIL will continue to flash until ignition is turned off. The ECU may clear the fault on next engine start, and the FIL will not flash unless fault is detected again. Vehicle will have to be test driven for at least 5 minutes to reset fault. When ECU detects a permanent fault, FIL will flash but fault will remain in ECU memory until physically erased.
Fault will be displayed by a flashing LED in tester. Connect LED Tester Tool (part number US 1115 or equivalent) to battery positive terminal and test connector No. 1. Access fault codes by inserting a fuse into top of fuel pump relay for 4 seconds, then remove fuse. Diagnostic terminals will be grounded and ECU memory will display any fault code via a flashing sequential code LED Tester Tool. See Fig 1 and Fig 2 .
Only one fault will be displayed and that fault code will be repeated until fuse is reinserted in fuel pump relay for 4 seconds and removed. Now the next stored fault code will be displayed. Continue with fuse insert/remove procedure until a Code 0000 is displayed indicating all fault codes have been displayed. Code 0000 is read when LED Tester Tool is lit for 2.5 seconds, then off 2.5 seconds, and continues this display with no pause in flashing.