Ignition System: Testing and Inspection

Electronic Ignition System Diagnosis

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) 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 1 voltage
* Ground
* IC
* Low reference

Diagnostic Aids

* Depending on the location in the spliced ignition voltage circuit, a slight to moderate resistance can cause a misfire or a crank/no start concern.
* Extended engine cranking time, will foul the spark plugs with excessive fuel and cause a crank/no start condition.

Reference Information
Schematic Reference

Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information
Special Tools

J 26792 Spark Tester

Circuit/System Verification

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


* 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 (Specifications) and Spark Plug Inspection (Testing and Inspection).

* If the engine will start, then observe the scan tool Misfire Current Cylinder parameters. This will indicate the affected ignition coil/modules.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the affected ignition coil/modules.
2. Ignition OFF for 90 seconds, test for less than 5 ohms between the ground circuit terminal 1 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal 2 and ground.

• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

4. Ignition ON, verify that a test lamp illuminates between the ignition 1 voltage circuit terminal 4 and ground.

• If the test lamp does not illuminate, test the ignition 1 voltage circuit for a short to ground or an open/high resistance.

5. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
6. Start the engine, observe the scan tool Misfire Current Cylinder parameters.

• If the misfire transfers with the suspect ignition coil/module, replace it.
• If the misfire does not transfer with the suspect ignition coil/module, replace the spark plug.

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)