Note. If an engine knock can be heard, repair engine mechanical problem before proceeding with circuit test.
Circuit Description
Knock Sensor (KS) is used to detect engine detonation, allowing PCM to retard Ignition Control (IC) spark timing based on KS signal being received. KS produces an AC signal so that under a no knock condition, signal on KS circuit measures about 0.007 volts AC. KS signals amplitude and frequency depend on amount of knock being experienced. PCM contains a non-replaceable knock filter module called a Signal-to-Noise Enhancement Filter (SNEF) module. Filter module determines whether knock is occurring by comparing KS circuit signal level with voltage level on noise channel. Noise channel allows PCM to reject and false knock signal by knowing amount of normal engine mechanical noise present. Normal engine noise varies depending on engine speed and load. When PCM determines that an abnormally low noise channel voltage is being experienced, DTC P0325 is set. Conditions for setting DTC
- Engine has been running for at least 30 seconds.
- PCM determines that its internal signal from its knock filter module indicates a continuous knocking condition for more than 10 seconds.
Diagnostic Aids
Check PCM and Knock Sensor (KS) connections. Ensure KS harness is not routed close to high voltage wires. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.