Chart A-1 No Service Engine Soon Light

Chart A-1 - No "Service Engine Soon" Light.:

Wiring Diagram for Chart A-1 - No "Service Engine Soon" Light:

CHART A-1 - NO "SERVICE ENGINE SOON" LIGHT

Circuit Description:

The "SERVICE ENGINE SOON" light is installed in the IPC. The light is powered by ignition 1 Ckt 39 and the ECM completes the ground to turn it "on". The light should be on with the engine not running however, 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 mode of the ECM. The system monitor button does not affect the "SERVICE ENGINE SOON" light.




Test Description: The following numbered steps correspond with the step numbers on diagnostic chart.

1. This step splits the circuit into two sections. A "SES" light on after grounding terminal "D" indicates the open is on the ECM side of the circuit. The "SES" light being off would indicate the fault is on the IPC side of the circuit.

2. If the test light did not light, the ECM is not powered up and CKT 439 or ECM connector must be repaired.

3. Checks to see if the open is in the IPC or Ckt 419. Since IPC terminal AA/AB is B+, a test light on, when connected between teminals "AA/AB" and "AJ", indicates that CKT 419 is complete through ALDL terminal "D" which has been jumpered to ground.

4. Checks to see if the open is in the ECM or Ckt 419. If the light is turned on by supplying a ground to the ECM harness terminal "A5", the fault is poor terminal contact at terminal "A5" or faulty ECM.




Diagnostic Aids:

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check For:

a. Poor Connection at ECM pin "A5" or IPC connector - Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connection.

b. Damaged Harness - Inspect harness for damage. If harness appears ok, observe "SERVICE ENGINE SOON" light while moving related connectors and wiring harness. A flickering light would indicate the intermittent fault location.