Chart A1-1 No Malfunction Indicator Lamp

No Malfunction Indicator Lamp - Part 1 0f 2:

No Malfunction Indicator Lamp - Part 2 0f 2:

OBD Circuit:

Circuit Description

There should always be a steady malfunction indicator lamp (MIL) when the ignition switch is in the "ON" position and the engine is not running. System voltage is applied to the indicator bulb. The engine control module (ECM) will control the MIL and turn it "ON" by providing a path to ground through the RED/YEL wire.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This determines if the engine will start.
2. This checks to see if the ECM is receiving power.
3. This checks for an open RED/YEL wire to the ECM or for a faulty ECM.
4. This checks to see if the EFI F-HTR relay switch is receiving power.
5. This checks to see if the ECM has a good ground.
6. This checks for an open RED/YEL wire to the instrument cluster.
7. This checks to see if the MIL is receiving power.
8. This checks to see if the EFI F-HTR relay coil is receiving power
9. This checks the EFI F-HTR ground wire for an open.
10. This checks the BLK/ORN wire between junction block I and the fuse and relay box for an open or for a faulty junction block I.


Diagnostic Aids:

Check EFI F-HTR, IGN and GAUGE fuses for opens and make sure EFI F-HTR Relay is securely mounted into the fuse and relay box.

An intermittent maybe caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.