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Electronic Ignition System Diagnosis

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    • Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The ignition system uses individual ignition coil/module assemblies for each cylinder. The engine control module (ECM) controls the individual coils by transmitting timing pulses on the ignition control (IC) circuit of each ignition coil/module to enable a spark event. Each ignition coil/module has the following circuits:

    • Ignition voltage
    • Ground
    • IC
    • Low reference

Diagnostic Aids
    • Depending on location in the spliced ignition voltage circuit, a slight resistance can cause a misfire or a crank/no start concern. A voltage drop test on the circuit will pinpoint this condition.
    • A slight to moderate resistance on any IC circuit can cause a misfire before DTC P0351-P0354 sets.
    • Extended engine cranking time, may foul the spark plugs with excessive fuel.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J 26792 HEI Spark Tester

Circuit/System Verification
  1. Verify that the engine is in good mechanical condition before continuing with this diagnostic.
  2. Verify the following conditions:
    3. • The ignition coil/modules are correctly connected
    • The proper firing order
    • The proper spark plug type
    • The proper spark plug gap and torque
      Refer to Ignition System Specifications and Spark Plug Inspection .

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the affected ignition coil/modules.
  2. Ignition OFF for 90 seconds, test for less than 5 ohms between the ground circuit terminal A and ground.
    3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Test for less than 5 ohms between the low reference circuit terminal B and ground.
    4. ⇒If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

    Important: If the ignition voltage fuse is open, it will be necessary to test the spliced ignition circuits and the components for a short to ground.

  4. Ignition ON, verify that a test lamp illuminates between the ignition voltage circuit terminal D and ground.
    5. ⇒If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance.
  5. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
  6. Start the engine, and observe the scan tool Misfire Current Cylinder parameters.
    7. ⇒If the misfire transfers with the suspect ignition coil/module, replace as needed.
  7. If the circuits test normal, test or replace the spark plug/s.

Component Testing

Use the J 26792 to verify the output of each ignition coil/module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Ignition Coil Replacement : LE5, LE9, or LAF
    •  Spark Plug Replacement
   


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