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
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:
* Ignition voltage
* Ground
* Ignition Control (IC)
* Low reference
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 IC 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 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 (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 Plug Tester
* J 35616-A/BT-8637 Connector Test Adapter Kit
Circuit/System Verification
1. Verify that the engine is in good mechanical condition before continuing with this diagnostic.
2. Verify the following conditions:
* The ignition coils/modules are correctly wired and connected
* The proper firing order
* 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) and Spark Plug Inspection (Testing and Inspection).
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 A and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Test for less than 5 ohms 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 ECM.
Important: 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 ignition coil/module with the ignition coil/module of a good cylinder.
6. Start the engine and observe the scan tool Misfire Current Cylinder parameters.
• If the misfire transfers with the suspect ignition coil/module, replace as needed.
7. If the circuits test normal, test or replace the spark plugs.
Component Testing
Use the J 26792 to verify the output of each ignition module/coil.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Engine Control Module Programming and Setup (V8) (Programming and Relearning)Engine Control Module Programming and Setup (V6) (Programming and Relearning)
* Engine Control Module Replacement (Service and Repair)
* Ignition Coil Replacement (Service and Repair)
* Spark Plug Replacement (Service and Repair)