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

The SERVICE ENGINE SOON (SES) light is located in the IPC. Light is powered by Ignition 1, circuit No. 39 and ECM completes system ground to turn light ON. With ignition ON, engine not running, light should be ON. If with engine running light is ON steady, this indicates an ECM code is set. When system diagnostics are entered, light should flash, indicating service mode of ECM has been entered. The system monitor button does not affect SERVICE ENGINE SOON light.

NOTE: Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits circuit into 2 sections. SERVICE ENGINE SOON light illuminating after grounding ALDL terminal "D" indicates open is on ECM side of circuit. SERVICE ENGINE SOON light staying OFF would indicate fault is on IPC side of circuit.

Test Number 2) With test light, check circuit No. 39 to ensure voltage is available to SES light bulb. Check body ignition 1 fuse No. 14 if test light does not light.

Test Number 3) If test light DID NOT illuminate when connected between ECM terminal BA 6 and ground, ECM is not getting power. This is result of an open or short to ground (blown fuse) in circuit No. 439.

Test Number 4) This step checks for open in IPC or circuit No. 419. IPC terminal D2 is 12 volts. When test light connected between terminals D2 and C9 illuminates, it indicates that circuit No. 419 is complete through ALDL terminal D , which has been grounded.

Test Number 5) This step checks for open in ECM or circuit No. 419. If test light illuminates when backprobed to ECM harness terminal YC11 (Brown/White wire), fault is from poor contact at terminal YC11 or a faulty ECM.