Chart A-1 Service Now or Soon Lights Inoperative

Chart A-1 - Part 1 Of 2:

Chart A-1 - Part 2 Of 2:

Service Telltale Circuit:

The Service Now and Service Soon telltales should illuminate during crank. The ECM will turn on the "Service Now" light by grounding circuit #419 and likewise the "Service Soon" by grounding circuit #499.

1. If the "Service Now" light does not illuminate during crank, ground the ALDL connector pin D with ignition on, and observe the "Service Now" Light. If the light does not illuminate, then check for an open in circuit #419 or a burned out bulb. If the light does illuminate with pin D grounded, backprobe P-3 ECM connector pin 4 with a jumper to ground. If the lamp will not illuminate, check for an open in circuit #419 from the ALDL connector to the ECM connector. If the Service Now Light illuminates with pin 4 jumpered to ground, then check for faulty mating of the ECM connector or for a faulty ECM.

2. If the Service Soon light does not illuminate during crank, then ground the ALDL connector pin E, with ignition on, and observe the Service Soon Light. If the light does not illuminate, then check for an open in circuit #499 or a burned out bulb.

If the lamp does illuminate with pin E grounded, backprobe P-3 ECM connector pin M with a jumper to ground. If the lamp does not illuminate check for an open in circuit #499 from the ALDL connector to the ECM connector. If the Service Soon Light illuminates with pin M jumpered to ground, then check for faulty mating of the ECM connector or for a faulty ECM.

3. If neither the Service Now or Service Soon illuminate during crank, enter diagnostics and note which codes are present.

A. If no codes were present, check the 20 amp gage fuse. If the fuse is okay then check for an open in circuit #39

B. Code E18 represents a problem in the crank circuit and should be diagnosed using the Code 18 Chart.

C. Code F32 suggests a problem with the ECM ignition, battery, or ground circuits. Check the 15 AMP ignition fuse and 20 AMP battery fuse, repair the short to ground present if the fuse is blown. If the fuses are O.K., check for an open in the ground and voltage feed circuits.