Circuit Description
WARNING: This page is about a different car, the 2007 Hummer H2. However, it is still accessible from the selected car via links, so may be relevant.
The knock sensors (KS) produce an AC signal under all engine operating conditions. When the engine is running, the powertrain control module (PCM) learns a minimum and maximum frequency of normal engine noise. The KS system monitors both knock sensors in order to determine if knock is present. If the KS system determines that excessive knock is present, the PCM retards the spark timing based on the signals from the KS. The PCM continues to retard timing until no knock is present. If the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system, DTC P0325 sets.