P0321

DTC P0321 Spark Reference Circuit Diagnostic Chart:

CIRCUIT DESCRIPTION
The spark reference signal (CKT 647) is used by the Powertrain Control Module (PCM) to improve ignition timing accuracy during crank and at engine speeds of up to 1200 RPM. The spark reference circuit allows the use of ignition control mode below 400 RPM, eliminating the need to utilize module mode during start-up, and also allows the PCM to calculate true crankshaft position in 1/6 the time that use of the fuel control reference signal would permit.

During normal operation, the PCM uses the spark reference signal to control ignition timing until the engine speed exceeds 1200 RPM, at which time the fuel control reference signal (CKT 430) is used.


DIAGNOSTIC TROUBLE CODE (DTC) PO321 WILL SET WHEN
^ The engine is running.
^ The PCM detects 150 fuel control reference pulses (50 crank revolutions), and no spark reference pulses.
^ Engine RPM is below 1200.


ACTION TAKEN (PCM WILL DEFAULT TO)
When conditions for setting DTC P0321 exist, the fuel reference signal is used by the PCM to control ignition timing advance. This condition will cause module mode to be used for ignition timing below 400 RPM and PCM controlled ignition timing to be degraded below 1200 RPM. DTC P0321 does not illuminate the Malfunction Indicator Lamp (MIL).

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Verifies that CKT 647 is not shorted to ground or open in the ignition jumper harness.
2. If a window on the harmonic balancer is interfacing with the 18X Hall-effect switch, the ignition control module will ground the spark reference signal. Starter may have to be bumped several times to obtain a voltage reading.
3. Voltage reading should be lower than that obtained with engine not running indicating a pulsed reference signal.

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

Check For:
^ Backed out connector terminals at Ignition Control Module or PCM in CKT 647.
^ If connections and harness check OK, try monitoring voltage on CKT 647 with a Digital Voltmeter (DVM) while moving the related wiring harness and connectors with the engine idling. This may help to isolate the location of the malfunction.