Service Now and/or Service Soon Lights On

Fig. 33 Fuel data wiring circuit:

The ``Service Now'' and ``Service Soon'' indicator lights are powered from the ignition switch through the 20 amp gauge fuse and circuit 39, Fig. 33.
1. If ``Service Now'' light only is lit, proceed as follows:
a. Turn ignition off, then disconnect ECM P-3 connector and turn ignition on.
b. If light remains lit, repair short to ground in circuit 419.
c. If light goes out, fault is in ECM connector or PROM installation, or in the ECM or PROM itself. Repair or replace as necessary.
2. If ``Service Soon'' light only is lit, proceed as follows:
a. Turn ignition off, then disconnect ECM P-3 connector and turn ignition on.
b. If light remains lit, repair short to ground in circuit 499.
c. If light goes out, fault is in ECM connector or PROM installation, or in the ECM or PROM itself. Repair or replace as necessary.
3. If ``Service Now'' and ``Service Soon'' lights are both lit, proceed as follows:
a. Check circuit 451 for a short to ground and circuit 6 for a short to voltage at ECM and repair as necessary.
b. If circuits are satisfactory, fault is in ECM connector or PROM installation, or in the ECM or PROM itself. Repair or replace as necessary.