Code P0321, Spark Reference Circuit: Notes

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

During normal operation, control module uses spark reference signal to control ignition timing until engine speed exceeds 1200 RPM, at which time fuel control reference signal circuit is used. Fuel reference signal is used by control module to control ignition timing advance when conditions for setting code are present. This condition will cause module mode to be used for ignition timing less than 400 RPM and control module controlled ignition timing to be degraded less than 1200 RPM. Code does not illuminate 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 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.