CodeXOBD

P0325 — Knock Sensor 1 Circuit Malfunction (Bank 1)

P0325 means the engine has lost its ability to hear detonation. Nothing fails immediately, but the module retards timing defensively — so expect less power and worse economy until it is fixed.

Moderate

The engine runs safely because the module retards timing as a precaution. Expect reduced power, worse economy, and possibly pinging under load on poor fuel. This code will cause an emissions test failure.

$30–$400Parts, typical range
0.5–4 hLabour
estimateNot a quote · 2026 basis

What P0325 means

A knock sensor is a piezoelectric microphone bolted to the block, tuned to the frequency of detonation. When it hears knock the module retards ignition timing enough to stop it. P0325 means the module is not receiving a signal it can use, so it can no longer detect knock and falls back on a conservative timing map to protect the engine. That protection is why the symptom is dullness rather than damage.

Technical summary
SystemPowertrain — ignition and misfire
How a misfire is detectedThe crankshaft sensor gives position and speed, the camshaft sensor gives which stroke, and the module times the coil and injector for each cylinder from both. It detects a misfire by the small deceleration of the crankshaft that follows a cylinder which failed to fire, and attributes it to a cylinder when the pattern is consistent.Crank sensorposition, speedCam sensorwhich strokeModuletimes the sparkCoil & injectorper cylinderA misfire is measured as crankshaft deceleration, not as a missing spark

Symptoms you may notice

What causes P0325

Knock sensor failed

Very likelymedium costmoderate

The piezoelectric element degrades with heat cycling and eventually stops producing a usable signal. Common on high-mileage engines and the most likely cause.

Sensor loose or over-tightened

Likelylow costmoderate

The sensor only hears the block if it is clamped to a precise torque. Loose, it hears nothing; over-tightened, its output distorts. This is a frequent consequence of previous work rather than a failure.

Common misdiagnosis

Fit the replacement to the specified torque with a wrench. Guessing here reproduces the fault with a new part.

Wiring or connector damaged

Possiblelow costmoderate

The sensor often sits under the intake manifold where the harness is hard to see and easy to pinch during other work. Its signal is small, so shielding damage alone can be enough.

The engine is genuinely knocking

Rarehigh costprofessional

Persistent heavy detonation from poor fuel, carbon build-up or overheating can present alongside sensor codes. Rule this out before dismissing the code as electrical.

How to diagnose it

1

Check timing correction in live data

Watch the ignition timing correction or knock retard value while the engine is loaded. A module that has given up on the sensor will show no correction at all.

Tools: OBD-II scanner with live dataIf it passes: Correction responds to load. The fault may be intermittent.If it fails: No correction is being applied. Continue to step 2.
2

Inspect the connector and harness

Locate the sensor — often beneath the intake manifold — and examine the connector and shielding for damage, corrosion and chafing.

Tools: Inspection lightIf it passes: The harness is sound. Continue to step 3.If it fails: Repair the wiring, clear the code and re-test.
3

Measure sensor resistance

Unplug the sensor and measure across its terminals, comparing against the specification. Most read in the high kilohm to megohm range and an open or shorted reading condemns it.

Tools: MultimeterIf it passes: Resistance is within specification. Suspect the harness shielding or the module input.If it fails: Out of specification. Replace the sensor.
4

Refit to the specified torque

When fitting the replacement, clean the mounting face and torque the bolt to the figure in the manual. The sensor cannot hear the block correctly at any other clamp load.

Tools: Torque wrenchExpected: The manufacturer torque figure, not hand-tightIf it passes: The code clears and timing correction returns.If it fails: The code returns with a correctly torqued new sensor. Investigate the harness and module input.

Related codes

P0330P0300

Common questions

Will P0325 damage my engine?

Not by itself. The module retards timing as a precaution when it cannot hear knock, which protects the engine at the cost of power and economy.

Why did power drop so much?

Without a working knock sensor the module cannot risk advanced timing, so it uses a conservative map for every condition. The loss is deliberate.

Is the sensor hard to reach?

Often, yes. On many V engines it sits under the intake manifold, which is why labour dominates the cost of this repair.

Last verified 2026-07-27 · Sources: SAE J2012 — Diagnostic Trouble Code Definitions and Failure Type Byte (SAE International)

This information is for general guidance and is not a substitute for professional diagnosis. Cost figures are estimates, not quotes.