Knock Sensor 1 Circuit Malfunction (Bank 1)

The knock sensor is basically a microphone bolted to the engine block. It listens for the specific vibration frequency of detonation (knock) so the PCM can pull timing to protect the engine. P0325 sets when the signal is missing, shorted, or noisy. When this code is active the PCM defaults to a conservative timing map — engine still runs but you lose power and fuel economy.

Knock sensor signal voltage out of range or no signal at all when the engine is running and should be producing background noise.

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

1. 1Check connector and wire from sensor to PCM for damage / heat melt.
2. 2Measure sensor resistance — out of spec = bad.
3. 3Verify the sensor is torqued to spec (often ~15 ft-lb, varies).
4. 4Scope the signal at idle, then tap the block nearby with a small hammer — should see voltage spike.

• Failed knock sensor
• Broken / chafed wire (often where harness runs near manifold heat)
• Corroded connector
• Loose mounting bolt (sensor needs solid contact with block)
• Wrong torque on the sensor (over- or under-torqued kills them)

$150 (top-mount sensor) to $800 (under-intake on V6/V8).