Chart A-2 Service Now and/or Soon Light ON/No Codes Present

Chart A-2:

Service Telltale Circuit:

The "Service Soon" and "Service Now" lights are powered from the ignition switch through the 20 amp gage fuse and circuit #39.

1. The ECM supplies ground to the "Service Now" light through circuit #419. If this wire is shorted to ground, the "Service Now" light will be on whenever the ignition switch is on. No vehicle performance problems are caused by a shorted circuit #419.

2. The ECM supplies ground to the "Service Soon" light through circuit #499. If this wire is shorted to ground, the "Service Soon" light will be on whenever the ignition switch is on. No vehicle performance problems are caused by a shorted circuit #499.

3. Both the "Service Soon" and "Service Now" lights will be on with no codes set if a short to voltage is present on the crank signal input to the ECM (circuit #806).

4. If all the wiring circuits are OK, them the PROM and ECM must be investigated for faulty malfunctions.