Electronic Ignition (EI) System Diagnosis

ELECTRONIC IGNITION (EI) SYSTEM DIAGNOSIS

DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
The ignition system uses individual ignition coil/module assemblies for each cylinder. The engine control module (ECM) controls the individual coils by transmitting timing pulses on the ignition control (IC) circuit of each ignition coil/module to enable a spark event. Each ignition coil/module has the following circuits:
- An ignition voltage circuit
- A ground circuit
- An IC control circuit
- A low reference circuit

CIRCUIT/SYSTEM VERIFICATION
Observe the Computers and Control Systems Schematic for the ignition coils/modules, and review the Ignition System Specifications and the spark plug inspection procedure to verify the following:
- The ignition coil/modules are correctly connected
- The proper firing order
- The proper spark plug type
- The proper spark plug gap and torque. Refer to Ignition System Specifications and Spark Plug Inspection. Testing and Inspection
- A high resistance on any IC control circuit can cause a misfire before DTC P0351-P0354 sets.

CIRCUIT/SYSTEM TESTING

IMPORTANT: Verify that the engine is in good mechanical condition before continuing with this diagnostic.
1. Turn ON the ignition.
2. Inspect the fuse that supplies voltage to the ignition coil/modules.
- If the fuse is open, then test the spliced circuits and the individual ignition coil/modules for a short to ground.
3. Disconnect the affected ignition coil/module.
4. Connect a test lamp between the ignition coil/module ignition 1 voltage circuit and a good ground.
5. With the test lamp still connected, measure for battery voltage between the ignition 1 voltage circuit and a good ground.
- If the voltage is not within 1 volt of battery voltage, repair the high resistance or the open in the ignition 1 voltage circuit.
6. Turn OFF the ignition, and all electrical accessories. Allow sufficient time for all of the control modules to power down before taking a resistance measurement.
7. Measure for a proper value of less than 5 ohms of resistance between the ground circuit of the affected ignition coil/module and a good ground.
- If the resistance is more than 5 ohms, repair the high resistance or the open in the ground circuit.
8. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
9. Start the engine and observe the scan tool.
- If the misfire transfers with the suspect ignition coil/module, replace as needed.
- If the misfire does not transfer with the suspect ignition coil/module, observe the component testing procedures below, and replace the spark plug if needed.

COMPONENT TESTING
- Use the Spark Plug Inspection procedure to verify the integrity of the spark plugs. Refer to Spark Plug Inspection. Testing and Inspection
- Use the J 26792 Spark Tester to verify the output of each ignition coil/module.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Ignition Coil(s) Replacement
- Spark Plug Replacement. Verification Tests