Code P0321, Spark Reference Circuit: Notes

PCM uses the spark reference signal circuit to improve ignition timing accuracy during crank and at engine speeds up to 1200 RPM. The spark reference circuit allows use of ignition control mode at speeds less than 400 RPM, eliminating the need to utilize module mode during start-up, and also allows PCM to calculate true crankshaft position in 1/6 the time that use of fuel control reference signal would permit.

During normal operation, PCM uses spark reference signal to control ignition timing until engine speed exceeds 1200 RPM, at which time the fuel control reference signal circuit is used. Code P0321 will set when the following conditions are present.

• PCM detects 150 fuel control reference pulses (50 crank revolutions) and no spark reference pulses.
• Engine speed is less than 1200 RPM.
• Engine running.

Fuel reference signal is used by PCM to control ignition timing advance when conditions for setting Code P0321 are present. This condition will cause module mode to be used for ignition timing less than 400 RPM and PCM controlled ignition timing to be degraded less than 1200 RPM. Code P0321 does not illuminate the Malfunction Indicator Light (MIL).

1. Verifies short to ground is not present in spark reference circuit, or an open is not present in ignition jumper harness.
2. Ignition control module will ground spark reference signal if a window on harmonic balancer is interfacing with the 18X Hall Effect switch. 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.