Ignition System: Testing and Inspection

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 circuit of each ignition coil/module to enable a spark event.

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 will pinpoint this condition.
- A slight to moderate resistance on any ignition control 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 [1][2]Electrical Diagrams

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 Testing

1. Ignition OFF, disconnect the harness connector at the affected T8 ignition coil/modules.
2. Ignition OFF, all vehicle systems OFF. This may take up to 2 minutes. Test for less than 5 ohms between the ground circuit terminal A/1 and ground.
3. If greater than the specified range, test the ground circuit for an open/high resistance.
4. Test for less than 5 ohms between the low reference circuit terminal B/2 and ground.
5. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20 ECM.
6. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal D/4 and ground.
7. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
8. Exchange the affected T8 ignition coil/module with the T8 ignition coil/module of a good cylinder.
9. Start the engine, and observe the scan tool Misfire Current Cylinder parameters.
10. If the misfire transfers with the suspect T8 ignition coil/module, replace as needed.
11. If the circuits test normal, test or replace the spark plug/s.

Component Testing

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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Ignition Coil Replacement
- Spark Plug Replacement