Circuit Description
WARNING: This page is about a different car, the 1998 GMC Forward Control and 1998 Chevrolet Forward Control. However, it is still accessible from the selected car via links, so may be relevant.
VCM utilizes knock sensors to detect engine detonation, allowing VCM to retard Ignition Control (IC) spark timing based on knock sensor signal received. Knock Sensor (KS) circuitry within sensor pulls down VCM-supplied 5-volt DC signal, so that under a no-knock condition signal on KS, circuit measures about 1.3 volts. Sensor produces an AC signal that rides on DC signal. Signal amplitude and frequency are dependent upon amount of knock experienced.
VCM contains a replaceable KS module. KS module contains circuitry that allows VCM to utilize KS signal and diagnose knock sensors and circuitry. VCM will set DTC if KS module is missing or faulty causing a continuous knock condition.
Conditions for setting DTC:
- DTC P0327 is not set.
- Engine has been running for at least 120 seconds.
- System voltage is greater than 10 volts but less than 17.1 volts.
- VCM detects a problem with KS module circuitry that causes a continuous knock condition.
- Conditions are present for up to .5 second.