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 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 coil assemblies in firing order sequence. Each ignition coil has the following circuits:
* An ignition voltage circuit
* A ground circuit
* An ignition control 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 EL 35616-E - 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.
* A slight to moderate resistance in the ignition voltage circuit can cause a misfire condition 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 ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Electronic Ignition System Description (Electronic Ignition System Description)
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)
Special Tools
* EL 35616-E - GM-Approved Terminal Test Kit
* EL 26792 - HEI Spark Tester
For equivalent regional tools, refer to Special Tools (Tools and Equipment).
Circuit/System Verification
Note: Verify that the engine is in good mechanical condition before continuing with this diagnostic.
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 (Application and ID).
Circuit/System Testing
1. Turn OFF the ignition.
Note: If the ignition fuse F9 is open, it will be necessary to test the spliced ignition circuits and the components for a short to ground.
2. Inspect the fuse that supplies ignition voltage to the ignition module/coils.
• If F9 fuse is open, test all ignition voltage circuits to the T8 Ignition Coil for a short to ground.
3. Disconnect the T8 Ignition Coil connector.
4. Replace the open F9 fuse with a new fuse.
5. Ignition ON, engine OFF.
6. Reconnect the T8 Ignition Coil connector.
• If the F9 fuse opens when connecting the T8 Ignition Coil, then replace the T8 Ignition Coil.
7. Ignition OFF, disconnect the T8 Ignition Coil connector.
8. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal A and ground.
• If the test lamp does not illuminate test the T8 Ignition Coil ignition voltage circuit for an open/high resistance.
9. Verify that a test lamp illuminates between the T8 Ignition Coil ground circuit terminal B and B+.
• If the test lamp does not illuminate, test the T8 Ignition Coil ground circuit for an open/high resistance.
10. Exchange the affected T8 Ignition Coil assembly with a known good assembly.
Note: An open/high resistance on the low reference circuit to the T8 Ignition Coil module may cause a misfire.
11. Start and idle the engine. Observe the misfire counters on the scan tool.
• If the misfire or crank/no start is resolved, replace the T8 Ignition Coil assembly.
• If the misfire does not transfer with the suspect T8 Ignition Coil, measure the resistance of the control circuit. The control circuit should measure less than 5 ohm. If the circuit tests normal, replace the K20 Engine Control Module.
Component Testing
Static Test
* 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.
Note: An erratic or weak spark is considered a no spark condition.
* Use the EL 26792 - HEI Spark Tester to verify the output of the T8 Ignition Coil. If no spark is detected across the gap of the spark plug tester, replace the T8 Ignition Coil assembly.
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)
* Control Module References (Programming and Relearning)for ECM replacement, setup, and programming