P0327: Low knock-sensor bias on either signal or return

P0327 detects an out-of-range low electrical condition in the Bank 1 knock-sensor circuit. The cited GM design uses a three-resistor bias network at each controller input to create a diagnostic DC voltage. This is separate from interpreting the vibration waveform as combustion knock.

Either side of the circuit matters

The threshold is below eight percent of the five-volt reference on the sensor input or return line. The return is therefore part of the monitored evidence; investigating only the named signal conductor can miss the channel the controller judged low.

The diagnostic runs with engine speed above zero and below 8,500 rpm. It counts 50 failures out of 63 samples at 100-millisecond intervals and uses Type A reporting. A transient or intermittent historical event may not be visible in a later ordinary scan reading.

Do not interpret low bias as a quiet engine

An out-of-range DC diagnostic level is not proof that the engine produces too little vibration or that the sensor needs tighter mounting. Those are different performance questions. The appropriate next check is the integrity of the biased input/return circuit under the applicable service procedure.

Preserve both line measurements if supported, reference status and event timing. After diagnosis, verify the enabled bias-range monitor passes on the affected channel. The source provides no generic sensor-resistance target, pinout or component-replacement rule.

Source and applicability

This explanation is limited to the 2025 GM 25OBDG03A monitor on page 263. Its thresholds are calibration examples, not universal specifications. Confirm the vehicle, engine and controller procedure before applying them.