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 circuits to the individual ignition module/coil assemblies in firing order sequence.

Diagnostic Aids

* Depending on location in the spliced ignition voltage circuit, a slight resistance can cause a misfire or a crank/no start condition. A voltage drop test on the circuit will pinpoint this condition.
* A slight to moderate resistance on any ignition control circuit can cause a misfire before DTC P0351-P0358 sets.
* Extended engine cranking time may foul the spark plugs with excessive fuel.
* 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 - GM-Approved Terminal Test Kit 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 ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
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 (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate T8 ignition coil/modules.
2. Ignition OFF, all vehicle systems OFF, it may take 2 minutes for all vehicle systems to power down, test for less than 5 ohm between the ground circuit terminal A and ground.

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

3. Test for less than 5 ohm between the low reference circuit terminal B 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 K20 ECM.

Note: If the ignition fuse is open, it will be necessary to test the spliced ignition circuits and the components for a short to ground.

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

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

5. Exchange the affected T8 ignition coil/module with the T8 ignition coil/module of a good cylinder.
6. Start the engine and observe the scan tool Cylinder 1-8 Current Misfire Counters.

• If the misfire transfers with the suspect ignition coil/module, replace as needed. The misfire should not follow the coil exchange.

7. If the circuits test normal, test or replace the spark plugs.

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)