Malfunction Indicator Lamp (MIL) Inoperative

Diagnostic Chart:

Schematic:

CIRCUIT DESCRIPTION
There should be a steady Malfunction Indicator Lamp (MIL) with the ignition ON and the engine not running. Ignition feed voltage is supplied directly to the MIL. The Powertrain Control Module (PCM) turns ON the MIL by grounding the MIL Control circuit. No MIL with the key ON, engine not running and the MIL DTC set suggests an open in the MIL Control circuit.

MIL OPERATION
The Malfunction Indicator Lamp (MIL) is located on the instrument panel and is displayed as CHECK ENGINE lamp.

MIL Function
^ The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible
^ The MIL illuminates during a bulb test and a system test
^ A DTC will be stored if a MIL is requested by the diagnostic

MIL ILLUMINATION
^ The MIL will illuminate with ignition switch ON and the engine not running
^ The MIL will turn OFF when the engine is started
^ The MIL will remain ON if the self-diagnostic system has detected a malfunction
^ The MIL may turn OFF if the malfunction is not present
^ If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is ON.
^ If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

DIAGNOSTIC AIDS
Inspect the following items:
^ If the engine runs OK, test for a malfunctioning MIL, an open in the MIL control circuit, or an open in the instrument cluster ignition feed.
^ If the engine cranks but will not run, test for an open PCM ignition, battery feed, or a poor PCM to engine ground.

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection-Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Diagrams.
^ Damaged harness-Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Diagrams.
^ PCM and engine grounds for clean and secure connections

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table:
2. If the MIL, DTC is set, the MIL Control Circuit table will better diagnose the condition.
6. Using a test lamp connected to B+, probe each of the PCM ground terminals to ensure that a good ground is present.