Ignition System: Testing and Inspection

ELECTRONIC IGNITION (EI) SYSTEM DIAGNOSIS

CIRCUIT DESCRIPTION
The powertrain control module (PCM) controls the 6 individual coil assemblies using reference pulses from the crankshaft position (CKP) sensor and other sensor inputs. Ignition 1 voltage is applied to the ignition coil assemblies when the ignition switch is in the ON or START positions. The ignition control module within each coil assembly toggles the primary windings, inducing a high voltage in the secondary windings. The high voltage induced in the secondary windings of the ignition coils is applied through the coil boots to the spark plugs.

DIAGNOSTIC AIDS
Inspect for the following conditions:

If the operation of the ignition system is intermittent, check for a reliable reference signal from the crankshaft position (CKP) sensor while cranking the engine. The PCM relies on the CKP sensor for engine reference. Without continuous accurate reference signals, there is no reliable spark or fuel injector pulse. The scan tool engine speed display should be more than 200 RPM while cranking. If erratic values, such as sudden spikes in engine speed are displayed, the engine reference signal may not be stable enough for the engine to start and run properly. Inspect the CKP sensor signal circuits for electromagnetic interference (EMI) or poor electrical connections.

A vehicle that starts and runs after being brought to the shop for an engine cranks but will not run concern, may have an ignition system that is susceptible to moisture. Spray water on the ignition system components and wiring in order to check for an engine miss or stall.

An intermittent malfunction may be caused by a condition in the ignition system electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-11:

Steps 12-18:

The numbers below refer to the step numbers on the diagnostic table.
4. If the PCM does not detect a signal from either CKP sensor, the engine will not start. Damage wiring or a sensor that is disconnect causes this condition. If an engine speed is observed, there is no voltage available to the ignition coils. An open fuse in the supply circuit causes a no start and no communication with the scan tool.
5. This step is tests for a condition with the control circuit of the ignition coil. If the voltage is not within the specified range, There is a condition with the control circuit of the ignition coil.
16. After replacing the PCM, a new minimum throttle position and idle speed must be established.