Service Now and/or Service Soon Light Inoperative

Fig. 35 Service telltale wiring circuit. 1985:

1985

1. Turn ignition on and observe coolant temperature light. If light is not lit, proceed to step 2. If light is lit, proceed as follows:
a. Crank engine and note ``Service Now'' and ``Service Soon'' lights. If only ``Service Now'' light is illuminated, check for burned bulb or open in circuit 499. If circuit and bulb are satisfactory, check for defective ECM connector or ECM.
b. If only ``Service Soon'' light is illuminated, connect a jumper wire from ALDL pin D to ground with ignition on and observe ``Service Now'' light. If light is on, check for open in circuit 419. If circuit is satisfactory, check for defective ECM connector or ECM. If light is off, check for burned out bulb or open in circuit 419.
2. If coolant temperature light does not illuminate when ignition is turned on, proceed as follows:
a. Check engine and note ``Service Now'' and ``Service Soon'' lights. If lights are on, check for burned out temperature bulb or open in circuit 35. If bulb and circuit are satisfactory, check for defective ECM connector or ECM.
b. If service lights are off when cranking engine, check 20 amp gauge fuse. If fuse is blown, repair short in circuit 39. If fuse is not blown, measure voltage at fuse with ignition on. If zero volts is measured at fuse, locate and repair open in fuse feed circuit. If 12 volts is measured at fuse, locate and repair open in circuit 39.