fault code guide
P0325: Knock Sensor 1 Circuit Malfunction (Bank 1)
The engine computer has lost reliable communication with knock sensor 1. Your car will dial back engine power to prevent internal damage.
How it shows up: The amber engine management light stays lit on your dashboard, and you may notice sluggish acceleration or poor fuel economy. The specific P0325 code is confirmed using an OBD scanner.
Updated 9 November 2026
Can I keep driving?
Service soon
Your car will pull back ignition timing to protect the engine, causing sluggish performance and higher fuel consumption until it is repaired.
What to do right now
- 1Check your instrument cluster to confirm the engine management light is steady amber, not flashing.
- 2Drive gently and avoid heavy acceleration, towing, or driving up steep hills at high revs.
- 3Book an inspection with a local garage or prepare to check the wiring once the engine is cold.
Likely causes
Most likely first.
- Likely
Damaged sensor wiring or loose connector
The knock sensor sits on the hot engine block, making its wiring prone to heat degradation, brittle insulation, or rodent damage. A broken wire or loose plug interrupts the sensor voltage signal entirely.
- Likely
Failed knock sensor
Inside the knock sensor, a small piezoelectric crystal detects vibrations. Over time, engine heat and vibration cause the crystal or internal resistor to fail, breaking the circuit.
- Possible
Corroded connector terminals
Road spray, moisture, or spilled fluids can seep into the wiring connector over time. This corrosion increases electrical resistance until the computer considers the circuit broken.
- Rare
Incorrect mounting torque or sensor placement
If work was recently carried out near the engine block, an over-tightened or under-tightened knock sensor will distort readings and set an electrical circuit fault.
What you can check yourself
Park somewhere safe and level, engine off, before you start.
- 1
Park safely and let the engine cool
Switch off the ignition and allow the engine bay to cool completely before opening the bonnet. Knock sensors sit directly against the engine block, which stays scalding hot after driving.
- 2
Inspect visible knock sensor wiring
Locate the knock sensor harness using your handbook or engine diagram. Look closely for pinched sections, chewed wires, melted loom insulation, or cracked connector clips.
- 3
Check the electrical plug connection
Gently disconnect the sensor plug if it is accessible. Check the metal pins inside for greenish corrosion or dirt, and ensure the plug clicks firmly back into place.
- 4
Listen for abnormal metallic engine noises
Start the engine and listen for sharp metallic pinging or rattling under load. If you hear metallic knocking, switch off immediately, as the engine cannot safely control combustion timing.
Rough cost to fix
Rough estimateTypical prices in Ireland (€) and the UK (£), from an independent garage up to a main dealer. The total repair cost depends heavily on whether the intake manifold must be stripped down to access the sensor location.
Wiring harness repair or plug replacement
- Do it yourself
- €15–45£12–40 in the UK
- At a garage
- €90–220£80–190 in the UK
Knock sensor replacement (accessible location)
- Do it yourself
- €40–110£35–95 in the UK
- At a garage
- €140–280£120–250 in the UK
Knock sensor replacement (under intake manifold)
- Do it yourself
- Garage job
- At a garage
- €280–550£240–480 in the UK
When to go to a garage
- You hear audible metallic pinging, rattling, or knocking sounds coming from the engine.
- The knock sensor is buried underneath the intake manifold and requires major stripping to reach.
- The engine management light begins flashing while driving, which indicates active cylinder misfiring.
- You have repaired the visible wiring or replaced the sensor, but code P0325 returns immediately.
Questions drivers ask
Can I keep driving my car with code P0325 present?
You can drive short distances to get home or reach a garage, provided the engine runs smoothly and the engine light is steady. The engine control unit will deliberately retard ignition timing to protect against knock, which noticeably reduces engine power and burns more fuel. Avoid towing, hard acceleration, or carrying heavy loads until it is repaired.
Will clearing code P0325 with a scanner fix the problem?
No, clearing the code will not solve the underlying fault. P0325 is an electrical circuit code, meaning the computer runs a continuous resistance check on the sensor. As soon as the computer runs its startup cycle or monitors the circuit again, it will register the abnormal voltage and switch the light straight back on.
Why does a knock sensor have to be tightened to an exact torque?
Knock sensors contain sensitive piezoelectric elements that turn mechanical vibrations into electrical voltage. If you tighten the mounting bolt too much, you crush the internal crystal and cause false readings; if it is too loose, vibration cannot transfer through the block properly. A garage will always use an accurate torque wrench to fit a new sensor.
Will fault code P0325 cause my car to fail the NCT or MOT?
For an MOT in the UK, an illuminated engine management light is an automatic failure for petrol cars first used from July 2003 and diesels from July 2008. On the Irish NCT, an engine light or stored code gives an Advisory Pass under current rules, but the car will fail if the retarded ignition timing raises exhaust emissions past legal limits.
Test rules here are for the National Car Test in Ireland (NCT) and the MOT in the UK. Elsewhere, check the regulations of your own country or state before going for a vehicle test.
The warning light you may see
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General guidance for most cars, not a diagnosis of yours. Details differ by make, model and year - check your handbook, and if in doubt, don't drive.