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Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the following:

CIRCUIT PIN IDENTIFICATION

Circuit PCM Pin No. Wire Color
MIL 18 Purple
NOTE: If MIL never comes on, start testing at step  2.

  1. MIL Always On

    Perform QUICK TEST . If any trouble codes are present, service as necessary before continuing. Turn ignition off. Disconnect PCM. Inspect harness connector for damage. Measure resistance of MIL circuit (Purple wire) between PCM connector terminal No. 18 and ground. If resistance is less than 10 k/ohms, repair short to ground in Purple wire between PCM and instrument panel. If resistance is greater than 10 k/ohms, replace PCM. Verify light operation.

  2. MIL Never On

    Turn ignition on. Using a test light, check fuse No. 29 in instrument panel fuse panel. If battery voltage is present at output side of fuse No. 29, go to step  4. If no voltage is present at output side of fuse No. 29, go to next step.

  3. Check Power Distribution

    Turn ignition on. Check for battery voltage at input side of fuse No. 29 in instrument panel fuse panel. If battery voltage is not present, repair power distribution. See appropriate wiring diagram in POWER DISTRIBUTION article in WIRING DIAGRAMS in appropriate lemon-25® manual. If battery voltage exists, replace blown fuse No. 29 (10-amp). Turn ignition on and recheck fuse No. 29. If fuse is blown again, check power supply for short to ground.

  4. Check MIL Bulb

    Turn ignition off. Remove instrument cluster. Remove MIL bulb. Measure continuity across bulb contacts. If continuity exists, go to next step. If continuity does not exist, replace bulb and verify operation.

  5. Check Power To Instrument Cluster

    Turn ignition off. Disconnect instrument cluster harness connector. Turn ignition on. Measure voltage between ground and Blue wire at instrument cluster harness connector. See Fig 1. Also see CIRCUIT PIN IDENTIFICATION  table. If battery voltage is present, go to next step. If battery voltage is not present, repair open Blue wire between fuse No. 29 and instrument panel harness connector.
    Fig 1: Identifying Instrument Cluster Connector Terminals
    G99I02338Courtesy of FORD MOTOR CO.

  6. Check MIL Circuit For Open

    Turn ignition off. Disconnect instrument cluster harness connector. Disconnect PCM. Inspect harness connector for damage. Measure resistance of MIL circuit between PCM connector terminal No. 18 (Purple wire) and instrument cluster connector. If resistance is less than 5 ohms, replace PCM. Verify MIL operation. If resistance is greater than 5 ohms, repair open Purple wire between PCM and instrument cluster harness connector. Verify MIL operation.
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