No Malfunction Indicator Lamp

NO MALFUNCTION INDICATOR LAMP




Circuit Description
When the ignition is turned ON, the Malfunction Indicator Lamp (MIL) will momentarily flash on and off, then it will remain on until the engine is running if no Diagnostic Trouble Codes (DTC) are stored. Battery voltage is supplied through the ignition switch directly to the MIL telltale. The powertrain control module (PCM)/engine control module (ECM) controls the MIL by providing a ground path through the MIL control circuit to turn on the MIL.

Diagnostic Aids
An open ignition #5 fuse will cause the entire cluster to be inoperative, and may set DTC P1625.
Check the battery and ignition feed circuits for poor connections if the MIL is intermittent.
Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminals-to-wiring connections or physical damage to the wiring harness.

Steps 1 To 12:

Steps 13 To 22:

Test Description
Number(s) below refer to the step number(s) on the diagnostic table.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on then scan tool, if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is stored in the scan tool for later reference.
3. Connections that are suspected of being faulty should be thoroughly checked as described in the diagnostic aids.
4. If the engine fails to start and the MIL is inoperative, then the fault can be isolated to either the PCM/ECM ignition feed, The battery feed, or a poor ground at the engine block, or the PCM/ECM.
6. Probing the MIL circuit with a test light to ground stimulates the PCM/ECM's control of the MIL. If the MIL illuminates, then the malfunction can be isolated to the control of the MIL or a poor connection at the MIL terminal to the PCM/ECM. Connections that are suspected of being faulty should be thoroughly checked as described in the diagnostic aids.
8. It takes very little resistance for the battery and ignition feed circuits to cause an intermittent condition and should also be checked for a poor connection as described in diagnostic aids.
11. Before replacing the PCM/ECM, check for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring harness. Replacement PCM/ECM's must be reprogrammed. Refer to Powertrain Control Module / Service and Repair.
20. PCM/ECM grounds will only cause a problem if all of the grounds are not making a good connection. If a PCM/ECM ground problem is suspected, the most probable place to check is where all the grounds meet, at the engine block.
22. If no faults have been found at this point and no DTCs were set, refer to the diagnostic aids.