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Test D12 - Ignition Diagnostic Monitor (IDM)

Fig 1: IDM Circuit
G72377
NOTE: Perform this test when Service Code 18 is displayed during QUICK TESTS or when directed here by other test procedures. The IDM circuit has a 20K-ohm resistor between Test Pin No. 4 and the ignition coil negative terminal.

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: ignition module, ignition coil, spark plugs and/or high tension cables, distributor and PIP sensor.

  1. Checking Continuity of IDM Circuit  - Turn key off and wait 10 seconds. Disconnect E-core ignition connector from coil. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box, leaving ECA disconnected. Set DVOM on 200K-ohm scale. Measure resistance between Test Pin No. 4 and ignition coil negative terminal. If reading is less than 20K ohms or greater than 24K ohms, repair open circuit and repeat QUICK TEST  . If reading is between 20K and 24K ohms, go to next step.
  2. Checking For Short to Ground  - Turn key off and wait 10 seconds. Leave breakout box installed and ECA disconnected. With DVOM on 200K-ohm scale, measure resistance between Test Pin No. 4 and Test Pins No. 40, 46, and 60. If any reading is less than 10K ohms, repair short to ground and repeat QUICK TEST  . If all readings are 10K ohms or more, go to next step.
  3. Checking TFI Module  - Turn key off and wait 10 seconds. Deactivate SELF-TEST. Using CONTINUOUS MONITOR (WIGGLE) TEST  , observe VOM or diagnostic tester for indication of fault while lightly tapping on TFI module and wiggling TFI harness connector. If fault is indicated, disconnect TFI harness. Inspect connector and terminals for damage. If connector and terminals are okay, check TFI ignition system. If no fault is indicated, go to next step.
  4. Checking EEC-IV Harness  - While in CONTINUOUS MONITOR (WIGGLE) TEST, observe VOM or diagnostic tester for indication of fault while wiggling, shaking, or bending small sections of harness while working from TFI connector toward firewall. Repeat process from firewall to ECA. Perform this test to check for faults in the following circuits:
    • PIP Open/Shorted to Ground: Check circuit at Test Pin No. 56.
    • SPOUT Shorted to Ground: Check circuit at Test Pin No. 36.
    • Ignition Ground Open: Check circuit at Test Pin No. 16.
    • IDM Open to Ground: Check circuit at Test Pin No. 4.
    • IDM Shorted to Power: Check circuit at Test Pin No. 4.

    Perform CONTINUOUS MONITOR (WIGGLE) TEST  on these circuits one at a time in order to isolate fault. If fault is indicated, isolate fault and repair harness. Repeat QUICK TEST  . If no fault is indicated, go to next step.

  5. Checking ECA and Harness Connectors  - Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion or loose wires. If connector is damaged, repair as necessary and repeat QUICK TEST  . If connector is okay, replace ECA. Start and run engine for one minute. Perform KEY ON ENGINE RUNNING (KOER) SELF-TEST  and observe codes. Connect ECA when step is completed.
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