Ignition System: Testing and Inspection

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

This ignition system uses individual ignition module/coil assemblies for each cylinder. The engine control module (ECM) controls the spark events by transmitting the timing pulses on the ignition control (IC) circuits to the individual ignition module/coil assemblies in firing order sequence. Each ignition module/coil has the following circuits:

* An ignition 1 voltage circuit
* A ground circuit
* An IC circuit
* A low reference circuit

Diagnostic Aids

* This test procedure requires that the vehicle battery has passed a load test and is completely charged.
* There is an adequate supply of fuel in the fuel tank.
* When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect both mating electrical terminals for corrosion and terminal tightness.
* Use the J 35616 for any test that requires probing the underhood fuse block terminals, component wire harness terminals, or the ECM wire harness terminals.

Reference Information
Schematic Reference

Engine Controls Schematics (except L96) ([1][2]Electrical Diagrams)Engine Controls Schematics (L96) ([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 Spark Plug Tester
* J 35616-A/BT-8637 Connector Test Adapter Kit

Circuit/System Verification

Observe the Engine Controls Schematic for the ignition module/coils, and review the Ignition System Specifications to verify the following concerns:

* The ignition modules/coils are correctly wired and connected
* The proper spark plug type
* The proper spark plug gap and torque
* The proper ohm values for the spark plug wires
Refer to Ignition System Specifications (Specifications).

Circuit/System Testing

1. Turn OFF the ignition.

Important: This engine application uses 2 fuses, one for each bank, to supply ignition 1 voltage to the ignition module/coil assemblies and also to the fuel injectors. A good indication that a fuse is open is that all 4 misfire counters are incrementing on one side of the engine


2. Inspect both fuses that supply ignition voltage to the ignition module/coils.

• If a fuse is open, test all 8 ignition voltage circuits to the ignition module/coils or the fuel injectors on that engine bank, for a short to ground.

3. Disconnect the 4 ignition module/coil, and the 4 fuel injector electrical connectors, for the engine bank that has the open fuse.
4. Replace the open fuse with a new fuse.
5. Ignition ON, engine OFF.
6. Reconnect each ignition module/coil, and fuel injector electrical connectors, one at a time.

• If the fuse opens when connecting an ignition module/coil or fuel injector electrical connector, then replace the component that caused the fuse to open.

7. Ignition OFF, disconnect the appropriate ignition module/coil electrical connector.
8. Ignition ON, verify that a test lamp illuminates between the ignition voltage circuit and ground.

• If the test lamp does not illuminate test the ignition voltage circuit for an open/high resistance.

9. Verify that a test lamp illuminates between the ignition module/coil ground circuit and B+.

• If the test lamp does not illuminate, test the ignition module/coil ground circuit for an open/high resistance.

10. Inspect and measure the resistance of the spark plug wire. Refer to Spark Plug Wire Inspection (Testing and Inspection) and Ignition System Specifications (Specifications).

• If the resistance value is not within the specified range, or does not pass the inspection, replace the spark plug wire.

11. Exchange the misfiring cylinder, ignition module/coil assembly with the ignition module/coil assembly from a non-misfiring cylinder.
12. Start and idle the engine. Observe the misfire counters on the scan tool.

• If the misfire transfers with the suspect ignition module/coil, then replace the ignition module/coil assembly.
• If the misfire does not transfer with the suspect ignition module/coil, then measure the resistance of the IC circuit. The IC circuit should measure less than 5 ohms. If the circuit tests normal, replace the ECM.

Component Testing

* Use the Spark Plug Inspection procedure to verify the integrity of the spark plugs. Refer to Spark Plug Inspection (Testing and Inspection). Replace the spark plug if necessary.

Important: An erratic or weak spark is considered a no spark condition.


* Use the J 26792 to verify the output of each ignition module/coil. If no spark is detected across the gap of the spark plug tester, then replace the ignition module/coil assembly.

Repair Instructions

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

* Engine Control Module Programming and Setup (Gasoline Engines) (Testing and Inspection)Engine Control Module Programming and Setup (LGH or LML) (Testing and Inspection)
* Engine Control Module Replacement (Service and Repair)
* Ignition Coil Replacement (Service and Repair)
* Spark Plug Replacement (Service and Repair)