Ignition System: Testing and Inspection

Electronic Ignition System Diagnosis (with LLT)

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 on this engine uses individual ignition coils and ignition control (IC) circuits for each cylinder. Ignition voltage is supplied to each bank of ignition coils. The engine control module (ECM) controls the ignition system operation. The ECM controls each coil using the IC circuits. The ECM commands the IC circuit low when a spark event is requested. The sequencing and timing are controlled by the ECM.

Diagnostic Aids

* The ignition coils for each bank are fused separately. If a fuse opens or the ignition voltage circuit opens between the fuse and the splice, all the ignition coils for one bank of the engine would be inoperative. If the ground circuit opens at the engine block, the ignition coils would be inoperative for one bank of the engine.
* Inspect the ignition coils for aftermarket devices. An aftermarket device connected to the ignition coil circuits, may cause a condition with the ignition coils.

Reference Information
Schematic Reference

Engine Controls Schematics (Electrical Diagrams)
Description and Operation

Electronic Ignition System Description (Electronic Ignition System Description)
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
* J 43244 Relay Puller Pliers

Circuit/System Testing

Note: Do not perform this diagnostic procedure if you were not sent here from a misfire DTC or the Engine Cranks but Does Not Run diagnostic.

1. Ignition OFF, disconnect the harness connector of the ignition coil.
2. Test for less than 5 ohm between each of the ground circuits listed below and ground.

* Ignition coil ground circuit terminal 3
* Ignition coil ground circuit terminal 4

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

3. Ignition ON, load test for battery voltage between the ignition voltage circuit terminal 2 and ground.

• If less than B+, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all the components connected to the ignition voltage circuit and replace as necessary.

Note: The average output of the IC circuit can be obtained by selecting the MIN/MAX function on the DMM.

4. Crank or start the engine. Test for an average output of greater than 100 mV between the appropriate IC circuit terminal 1 and ground.

• If less than the specified value, test the IC circuit for a short to ground or an open/high resistance. If the circuit/connection tests normal, replace the ECM.
• If greater than the specified value, test the IC circuit for a short to voltage. If the circuit/connection tests normal, replace the ECM.

5. If all circuits/connections test normal, replace the ignition coil.

Repair Instructions

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

* Ignition Coil Replacement - Bank 1 (LP1, LY7) (Service and Repair)
* Ignition Coil Replacement - Bank 2 (LP1, LY7) (Service and Repair)