The knock sensor (KS) system is used to detect engine detonation, allowing the engine control module (ECM) to retard the ignition control spark timing based on the KS signal being received. The KS produces an AC signal so that under a no-knock condition the signal on the KS circuit measures about 0.007 volts AC. The KS signal's amplitude and frequency depend upon the amount of knock being experienced. The ECM contains a non-replaceable knock filter module called a digitally controlled signal-to-noise enhancement filter (DSNEF) module. This filter module in the ECM determines whether or not knock is occurring by comparing the signal level on the KS circuit with the voltage level on the noise channel. The noise channel allows the ECM to reject any false knock signal by knowing the amount of normal engine mechanical noise present. Normal engine noise varies depending on engine speed and load. When the ECM determines that an abnormally low noise channel voltage level is being experienced, DTC P0325 will set.

Inspect and correct any abnormal engine noise before using the diagnostic table.

Any circuitry that is suspected as causing the complaint should be thoroughly inspected for the following conditions:

The numbers below refer to the step numbers on the diagnostic table.

1. The On-Board Diagnostic System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool, if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.

2. If the conditions for the test, as described above, are met, a DTC P0325 will set and the MIL will illuminate.

4. If the engine has an internal knock or audible noise that causes a knocking type noise on the engine block, the knock sensor may be responding to the noise.

6. The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.