P0326: A connected knock sensor with too little mechanical vibration

P0326 is a knock-sensor performance diagnostic for Bank 1 in this GM table. It targets an important distinction: the sensor may be electrically connected yet produce too little background signal because engine vibration is not transferred to it properly. The source specifically describes an unattached or loosely mounted sensor as the intended fault condition.

Background noise is useful evidence

The controller examines filtered intensity in a selected frequency range during non-knocking operation. A value below the applicable abnormal-noise threshold fails the monitor. It is not looking for excessive knock here; an unusually quiet signal is the concern.

The test requires engine speed above 2,000 rpm, air charge above 210 mg per cylinder and more than 267 accumulated revolutions above the minimum speed. Active Fuel Management and non-AFM operation use separate calibration thresholds. An idle-only observation cannot reproduce these conditions.

Mechanical coupling and electrical continuity

A circuit continuity check can pass while this monitor still fails. That makes sensor mounting history and the applicable mounting procedure meaningful alongside electrical evidence. The table supplies no tightening torque or universal location, so neither should be guessed.

Record operating mode, load and the filtered noise result. Confirm the correct threshold for that mode before condemning the sensor. Verification requires a completed background-noise performance test under eligible conditions, not simply a normal resistance reading or an absence of audible knock.

Source and applicability

This explanation is limited to the 2025 GM 25OBDG03A monitor on page 262. Its thresholds are calibration examples, not universal specifications. Confirm the vehicle, engine and controller procedure before applying them.