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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2007 🢒 Solstice 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Electronic Ignition (EI) 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:

    • An ignition voltage circuit
    • A ground circuit
    • An IC control circuit
    • A low reference circuit

Diagnostic Aids
    • Depending on the location in the spliced ignition voltage circuit, a slight resistance can cause a misfire or a crank/no start concern. To pinpoint this condition perform a voltage drop test on the circuit.
    • Extended engine cranking time, may foul the spark plugs with excessive fuel and cause a crank/no start condition.
    • The ECM will set a misfire DTC for a high resistance or an open on the ignition control (IC) circuits.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Electrical Information Reference

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

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls
    •  Scan Tool Snapshot Procedure

Special Tools Required

J 26792 Spark Tester

Circuit/System Verification

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

    • Observe the Engine Controls Schematic for the ignition coils/modules, and review the Ignition System Specifications and the spark plug inspection procedure to verify the following:
       - 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 .
    • If the engine will start, then observe the scan tool Misfire Current Cylinder parameters. This will indicate the affected ignition coil/modules, and if the condition is current.

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

    Important: If the ignition 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 circuit terminal 4 and ground.
    5. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  5. Ignition OFF, disconnect the ECM.
  6. Ignition OFF, test for less than 5 ohms of resistance between the ignition control (IC) circuit terminal 3 and the ECM.
    7. ⇒If greater than the specified value, test the circuit for an open/high resistance.
  7. Ignition OFF, connect the ECM.
  8. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
  9. Start the engine, observe the scan tool Misfire Current Cylinder parameters.
    10. ⇒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, refer to the Component Testing procedures below, and replace the spark plug if necessary.
    ⇒If the misfire does not transfer with the suspect ignition coil/module, and the Component Testing procedures do not isolate a fault, replace the ECM.

Component Testing
    • Use the Spark Plug Inspection procedure to verify the integrity of the spark plugs. Refer to Spark Plug Inspection .
    • 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.

    •  Control Module References for ECM replacement, setup, and programming
    •  Ignition Coil Replacement
    •  Spark Plug Replacement

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:

    • An ignition voltage circuit
    • A ground circuit
    • An IC control circuit
    • A low reference circuit

Diagnostic Aids
    • Depending on the location in the spliced ignition voltage circuit, a slight resistance can cause a misfire or a crank/no start concern. To pinpoint this condition perform a voltage drop test on the circuit.
    • Extended engine cranking time, may foul the spark plugs with excessive fuel and cause a crank/no start condition.
    • The ECM will set a misfire DTC for a high resistance or an open on the ignition control (IC) circuits.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Electrical Information Reference

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

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls
    •  Scan Tool Snapshot Procedure

Circuit/System Verification

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

    • Observe the Engine Controls Schematic for the ignition coils/modules, and review the Ignition System Specifications and the spark plug inspection procedure to verify the following:
       - 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 .
    • A moderate resistance on any IC control circuit can cause a misfire.
    • Extended engine cranking time, may foul the spark plugs with excessive fuel.
    • If the engine will start, then observe the scan tool Misfire Current Cylinder parameters. This will indicate the affected ignition coil/modules, and if the condition is current.

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

    Important: If the ignition 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 circuit terminal 4 and ground.
    5. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  5. Ignition OFF, disconnect the ECM.
  6. Ignition OFF, test for less than 5 ohms of resistance between the ignition control (IC) circuit terminal 3 and the ECM.
    7. ⇒If greater than the specified value, test the circuit for an open/high resistance.
  7. Ignition OFF, connect the ECM.
  8. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
  9. Start the engine, observe the scan tool Misfire Current Cylinder parameters.
    10. ⇒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, refer to the Component Testing procedures below, and replace the spark plug if necessary.
    ⇒If the misfire does not transfer with the suspect ignition coil/module, and the Component Testing procedures do not isolate a fault, replace the ECM.

Component Testing
    • Use the Spark Plug Inspection procedure to verify the integrity of the spark plugs. Refer to Spark Plug Inspection .
    • Use the J 26792 Spark Tester to verify the output of each ignition coil/module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Control Module References for ECM replacement, setup, and programming
    •  Ignition Coil Replacement
    •  Spark Plug Replacement