A-1 ~ No Malfunction Indicator Lamp (MIL)

Malfunction Indicator Lamp (MIL) Circuit:

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

Diagnostic Aids
An open ignition fuse will cause the MIL to be inoperative.
Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked for improper mating, broken locks, improperly formed or damaged terminals, or physical damage to the wiring harness.

Table A-1 - No Malfunction Indicator Lamp (MIL) (1 Of 2):

Table A-1 - No Malfunction Indicator Lamp (MIL) (2 Of 2):

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The OBD System Check prompts the Technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.
3. If the engine fails to start and the MIL is inoperative then the fault can be isolated to either PCM ignition feed, the battery feed, a poor PCM ground at the engine block, or the PCM.
4. A MIL that responds correctly to the scan tool command indicates that the fault is not present or that the condition that caused the "No MIL" condition has been corrected.
5. Probing the MIL circuit with a test light to ground simulates the PCM's control of the MIL. Whenever the MIL illuminates, then the fault can be isolated to the control of the MIL.
6. Locate and repair any shorts that may have caused the fuse to open before replacing the fuse.
11. Before replacing the PCM, check terminals for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness. Replacement
PCM must be reprogrammed. Refer to the latest Techline information for programming procedures.
20. PCM grounds will only cause a problem if all the a grounds are not making a good connection.

NOTE: Whenever a PCM ground problem is suspected, the most probable place to check is where all the grounds meet at the engine block.