P1351

DTC P1351 Electronic Spark Timing (EST) Output High Or Pulses Detected When Open:

Electronic Spark Timing (EST):

CIRCUIT DESCRIPTION
The enhanced ignition system provides timing input to the Vehicle Control Module-A (VCM-A) with a crank sensor. The VCM-A uses this reference pulse to determine individual ignition spark timing for each cylinder.

Once the VCM-A calculates ignition timing, the timing signal will be sent to the ignition coil module on the Ignition Control (IC) circuit. Each timing pulse received by the ignition coil module, on the IC circuit, will trigger the coil module to operate the ignition coil. Secondary ignition voltage is induced and is then sent to the distributor for distribution to each spark plug. DTC P1351 is a type "A" DTC.

The IC signal voltage ranges from about 0.5 volt to 4.5 volts.

DTC P1351 WILL SET WHEN
Voltage on CKT 423 exceeds 4.9 volts and engine speed is less than 250 RPM.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
The VCM-A will turn "ON" the Malfunction Indicator Lamp (MIL) (Service Engine Soon).

DTC P1351 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

DTC CHART TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This determines if the DTC is intermittent.
2. Without the engine running or cranking there would be no voltage present on the IC line.
3. This check determines if the IC signal from the VCM-A is available at the ignition coil driver. The IC circuit voltage should be between about 0.5 and 4.5 volts.
4. The remaining tests begin to check that the coil driver circuitry is OK.

DIAGNOSTIC AIDS
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check for:
^ Poor connection or damaged harness - Inspect VCM-A harness connectors for backed out terminals "GR9" and "BK18" improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
^ Intermittent test - If connections and harness check OK, monitor a digital voltmeter connected between VCM-A terminal "GR9" and "BK18" while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change. This may help to isolate the location of the malfunction.