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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 SLS 🢒 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
    • The ground circuit
    • An IC circuit
    • Low reference circuit

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Replacement
    •  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
    •  Engine Control Module Scan Tool Information

Special Tools

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:

    • 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 .

Circuit/System Testing

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

  1. Turn the ignition OFF.
  2. Inspect the fuse that supplies voltage to the ignition coil/modules.
    3. ⇒If the fuse is open, test the spliced circuits and the individual ignition coil/modules for a short to ground.
  3. Disconnect the affected ignition coil/module.
  4. Connect a test lamp between the ignition coil/module ignition 1 voltage circuit and a good ground.
  5. With the test lamp still connected, measure for battery voltage between the ignition 1 voltage circuit and a good ground.
    6. ⇒If the voltage is within 0.5 V of battery voltage, repair the high resistance or the open in the ignition 1 voltage circuit.
  6. 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.
  7. Measure for less than 5 ohms of a proper value between the ground circuit of the affected ignition coil/module and a good ground.
    8. ⇒If the resistance is more than 5 ohms, repair the high resistance or the open in the ground circuit.
  8. Change the affected ignition coil/module with the ignition/coil module of a good cylinder.
  9. Start the engine, and observe the scan tool.
    10. ⇒If the misfire occurs with the suspect ignition coil/module, replace as needed.
    ⇒If the misfire does not occur with the suspected ignition coil/module, observe the component testing procedures below, replace the spark plugs as needed.

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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Ignition Coil Replacement - Bank 1
    •  Ignition Coil Replacement - Bank 2
    •  Spark Plug Replacement