Powertrain, generic · Ignition system or misfire

P0325 Knock/Combustion Vibration Sensor A Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

The knock sensor is a piezoelectric structure-borne sound sensor bolted to the engine block; the module evaluates its signal per cylinder and retards ignition when it detects knock. Sensor A is the first sensor (bank 1 or a single sensor). With a fault the module retards ignition across the board as protection – noticeable loss of power and higher consumption. P0325 means the sensor circuit is open or the signal stays below the noise threshold. GM feeds a 20 kHz test signal into the circuit and detects an open circuit when it does not cancel out, setting the code in the first trip; Ford sees any open or short as a knock signal that is too small compared with the speed- and load-dependent noise level (at least 1,500 rpm, 35 % load, warm engine). Bulletins name moisture in the sensor (VW Touareg 3.6), engine software (GM Malibu 1.5) and chafed wiring (FCA).

Likely causes

Wiring or connector chafed, broken or corroded (sensor often under the intake manifold)
Knock sensor faulty (cracked piezo, moisture, heat damage)
Sensor loose or wrongly torqued
Engine software or diagnostic calibration
Engine module input stage

Symptoms

  • Check engine light on
  • Loss of power, sluggish response from ignition retard
  • Higher fuel consumption

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–600
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Check sensor torque
  2. Inspect wiring
  3. Measure sensor resistance where specified

Parts involved

knock sensor aknock sensor wiringengine control module

Related codes

P0326P0327P0328P0330P0324

References: gsi.ext.gm.com, newtonnet.co.uk, saabwisonline.com, static.nhtsa.gov.