DTC P0326: Excessive Spark Retard: Description

WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) uses a Knock Sensor (KS) to detect engine detonation, or spark knock. The knock sensor produces an AC signal at all engine speeds, and loads. The PCM makes adjustments to the spark timing based on the amplitude and frequency of the KS signal. The PCM uses the knock sensor to calculate the amount of normal engine noise (a noise channel) for a wide range of engine speeds and loads. The PCM compares the actual knock sensor signal to the learned noise channel. When the PCM detects a knock signal that varies outside the noise channel, the PCM will retard the spark timing until the knock goes away. If the knock is such that the vehicle operates on large amounts of spark retard, and the PCM is unable to eliminate the knock, this DTC will set.