Chart A-1, "Service Engine Soon" Light Inoperative: Notes
The "SERVICE ENGINE SOON" light is attached to the IPC. It is powered by ignition "3" circuit No. 39. The 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 field 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.
- This step splits the circuit into 2 sections. A light on after grounding terminal "D", indicates the open is on ECM side of split. A light off, indicates the open is on IPC side of circuit.
- 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.
- This test checks if open is in IPC or circuit No. 419. There should be battery voltage at IPC terminal "D2" when connected to terminal "C9" ("RBA" and "LT1" on Reatta and Riviera). Test light should illuminate, indicating circuit No. 419 is complete through ALDL terminal "D" which has been jumpered to ground.
- 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 or a faulty ECM.