Ignition System: Testing and Inspection

ELECTRONIC IGNITION (EI) SYSTEM DIAGNOSIS

CIRCUIT DESCRIPTION
Each engine cylinder has a dedicated ignition coil assembly. The ignition coil assembly contains the ignition module circuitry. The power distribution circuit supplies system voltage to each coil assembly when the ignition switch is in the ON or START positions. Each coil assembly regulates current flow through the primary coil windings, creating a magnetic field. The powertrain control module (PCM) signals each coil assembly to supply a spark in a cylinder through a trigger circuit. Each assembly does so by opening the primary circuit coil, inducing a high voltage in the secondary circuit coil. The high voltage in the secondary circuit grounds by arcing at the spark plug. This event creates a pulse on the fail safe circuit that the PCM recognizes as a confirmation of spark.

DIAGNOSTIC AIDS
Check for any of the following conditions:
- Any circuit malfunction between the ignition coil assembly and the PCM should set a fail safe circuit DTC P0351, P0352, P0353, or P0354.
- Check the crankshaft position (CKP) sensor engine reference signal with a scan tool. Observe the Engine Speed parameter while cranking the engine. The scan tool should indicate a steady 200-300 RPM while cranking. If erratic values, such as sudden spikes in the engine speed, are displayed, the engine reference signal is not stable enough for dependable ignition system operation.
- An ignition system that tests OK after sitting may be susceptible to moisture. Spray water on the ignition system components and wiring in order to check for an intermittent failure.

TEST DESCRIPTION

Step 1 - Step 11:

The numbers below refer to the step numbers on the diagnostic table.
2. If there is a fault in either the crankshaft position (CKP) sensor or camshaft position (CMP) sensor circuits, the ignition system can malfunction. Repair the cause of a DTC P0335 or DTC P0340 first.
3. If there is a fault in the electrical circuits between the PCM and the ignition coil assemblies, a DTC P0351-P0354 will set. Use the DTC P0351-P0354 diagnostic table in order to repair the ignition system failure.
7. This step checks for a condition that can cause a loss of spark, even though the test in step 4 indicated that there was good spark.
10. This step checks whether the engine will start and run. A repair that has been performed leading to this step may only have been a contributing cause of a no start condition. Returning to the Engine Cranks but Does Not Run diagnostic table will locate additional causes of the no start condition.