Chart A-1, No Service Engine Soon Light: Notes

The SERVICE ENGINE SOON light is attached to the IPC. It is powered by CPS circuit No. 812 and ECM completes the ground to turn the light on. The light will be ON while engine is not running. With the engine running, a steady light indicates an ECM code is set. When the engine is running and diagnostics are entered, a flashing light indicates the operating service mode of the ECM. The system monitor button will not affect the SERVICE ENGINE SOON light.

NOTE: Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits the circuit into 2 sections. A SES light on after grounding terminal "D", indicates the open is on ECM side of circuit split. With the SES light off, indicates the open is on IPC side of circuit.

Test Number 2) If test light does not light when connected between IPC terminal B12 and ground, feed circuit for the SES bulb is open.

Test Number 3) If test light did not illuminate when connected between ECM terminal BA6 and ground, ECM will not be powered up. This is a result of an open or short to ground (blown fuse) in circuit No. 439.

Test Number 4) This test checks if open is in IPC or circuit No. 419, since IPC terminal B12 is battery voltage. With test light connected between terminals B12 and L5, test light should illuminate, indicating circuit No. 419 is complete through ALDL terminal "D" which has been jumpered to ground.

Test Number 5) This test checks if open is in ECM or circuit No. 419. If test light illuminates when ECM terminal YC11 is grounded, fault is in a poor terminal contact at YC11 or a faulty ECM.