Knock Sensor: Description and Operation

PURPOSE
The ECM/PCM monitors the ESC signal to determine when engine detonation occurs

OPERATION
The Electronic Spark Control (ESC) system is comprised of a knock sensor and the ECM/PCM. The knock sensor is located in the engine block and sends a signal to the ECM/PCM to retard ignition timing during a spark knock condition. When the knock sensor detects detonation, the ECM/PCM retards timing in small increments of 2° (up to 10°) to reduce detonation. This allows the engine to use maximum spark advance to improve driveability and fuel economy.

The Mem-Cal used with this engine contains the functions which were part of remotely mounted ESC modules used on other GM vehicles. The ESC portion of the Mem-Cal then sends a signal to other parts of the ECM which adjusts the spark timing to retard the spark and reduce the detonation.

LOCATION
The knock sensor is located in the engine block.

DIAGNOSTIC NOTES:
Retarded timing can also be a result of excessive valve lifter, pushrod or other mechanical engine or transmission noise.