GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    â€¢ Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    â€¢ Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    â€¢  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:

    â€¢ An ignition voltage circuit
    â€¢ A ground circuit
    â€¢ An IC control circuit
    â€¢ A low reference circuit

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    â€¢  Engine Controls Connector End Views
    â€¢  Engine Control Module Connector End Views

Electrical Information Reference

    â€¢  Circuit Testing
    â€¢  Connector Repairs
    â€¢  Testing for Intermittent Conditions and Poor Connections
    â€¢  Wiring Repairs

Scan Tool Reference

    â€¢  Scan Tool Data List
    â€¢  Scan Tool Output Controls

Special Tools Required

J 26792 HEI Spark Tester

Circuit/System Verification

Observe the Engine Controls Schematic for the ignition coils/modules, and review the Ignition System Specifications to verify the following:

    â€¢ The ignition coil/modules are correctly connected
    â€¢ The proper firing order
    â€¢ The proper spark plug type
    â€¢ The proper spark plug gap and torque
        Refer to Ignition System Specifications .

Circuit/System Testing

Important: Verify that the engine is in good mechanical condition before continuing with this diagnostic.

  1. Turn OFF the ignition.
  2. Inspect the fuse that supplies voltage to the ignition coil/modules.
  3. ⇒If the fuse is open, then test the spliced circuits and the individual ignition coil/modules for a short to ground.
  4. Disconnect the affected ignition coil/module.
  5. Connect a test lamp between the ignition coil/module ignition 1 voltage circuit and a good ground.
  6. Turn ON the ignition.
  7. With the test lamp still connected, measure for battery voltage between the ignition 1 voltage circuit and a good ground.
  8. ⇒If the voltage is not within 1 volt of battery voltage, repair the high resistance or the open in the ignition 1 voltage circuit.
  9. Turn OFF the ignition, and all electrical accessories. Allow sufficient time for all of the control modules to power down before taking a resistance measurement.
  10. Measure for a proper value of less than 5 ohms of resistance between the ground circuit of the affected ignition coil/module and a good ground.
  11. ⇒If the resistance is more than 5 ohms, repair the high resistance or the open in the ground circuit.
  12. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
  13. Start the engine and observe the scan tool.
  14. ⇒If the misfire transfers with the suspect ignition coil/module, replace as needed.
    ⇒If the misfire does not transfer with the suspect ignition coil/module, observe the component testing procedures below, and replace the spark plug if needed.

Component Testing

    â€¢ Use the Spark Plug Inspection procedure to verify the integrity of the spark plugs. Refer to Spark Plug Inspection .
    â€¢ 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.

    â€¢  Ignition Coil Replacement - Bank 1
    â€¢  Ignition Coil Replacement - Bank 2
    â€¢  Spark Plug Replacement