Electronic Ignition (EI) System Diagnosis

Electronic Ignition System Diagnosis

Diagnostic Instructions

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

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 IC circuit can cause a misfire before DTC P0351-P0355 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 Connector End Views By Name
Electrical Information Reference

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

Scan Tool Reference

Control Module References Control Module References for scan tool information
Special Tools

J 26792 HEI Spark Tester

Circuit/System Verification

1. Start and idle the engine.
2. Observe the scan tool Misfire Current Cyl. parameters. This will indicate the affected ignition coil/modules, and if the condition is current.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Refer toSpark Plug Inspection Testing and Inspection and Ignition System Specifications [1][2]Specifications.

Circuit/System Testing

1. Turn OFF the ignition.
2. Disconnect the ECM.
3. Test the affected IC circuit terminal B for an open, a high resistance, a short to ground and for a short to voltage.

• If a fault is found, repair the circuit as needed.

4. Connect the ECM.
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.

• If the DTC or the misfire transfers with the suspect ignition/coil module, replace as needed.
• If the DTC or the misfire does not transfer with the suspect ignition/coil module, replace the ECM.

Component Testing

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

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Ignition Coil Replacement Service and Repair
* Spark Plug Replacement Service and Repair