Ignition Timing: Testing and Inspection

Continuity and Out-of-Range Value Check
This diagnosis detects open circuit or short-circuiting in the Electronic Spark Timing (EST) line by monitoring EST signals. A failure determination is made when the signal voltage remains higher or lower than the threshold for corresponding fault code beyond a predetermined time period.




Diagnosis enabling conditions are as follows:
- RPM is higher than the specified threshold.
- EST line is enabled.

The PCM provides a zero volt (actually about 100 mV to 200 mV) or a 5-volt output signal to the ignition control (IC) module. Each spark plug has its own primary and secondary ignition coil assembly ("coil-at-plug") located at the spark plug itself. When the ignition coil receives the 5-volt signal from the PCM, it provides a ground path for the B+ supply to the primary side of the coil-at -plug module. When PCM shuts off the 5-volt signal to the ION sensing module, the ground path for the primary coil is broken The magnetic field collapses and induces a high voltage secondary impulse which fires the spark plug and ignites the air/fuel mixture.

The circuit between the PCM and the ignition coil is monitored for open circuits, shorts to voltage, and shorts to ground. If the PCM detects one of these events, it will set one of the following DTCs:
- P0351: Ignition coil Fault on Cylinder #1
- P0352: Ignition coil Fault on Cylinder #2
- P0353: Ignition coil Fault on Cylinder #3
- P0354: Ignition coil Fault on Cylinder #4
- P0355: Ignition coil Fault on Cylinder #5
- P0356: Ignition coil Fault on Cylinder #6

The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. To provide optimum driveability and emissions, the PCM monitors the input signals from the following components in order to calculate spark timing:
- Engine coolant temperature (ECT) sensor.
- Intake air temperature (IAT) sensor.
- Mass air flow (MAF) sensor.
- PRNDL input from transmission range switch.
- Throttle position (TP) sensor.
- Vehicle speed sensor (VSS) .
- Crankshaft position (CKP) sensor.