Knock sensor electrical fault.
P0325 — also written PO325, P 0325, 0325 — is the OBD-II code for knock sensor 1 circuit (bank 1). Same code, same fix: this page covers every spelling of it.
This code means the ECU can't hear the 'heartbeat' of your engine, so it plays it safe by retarding the timing. It’s incredibly common on high-mileage Jap imports and older Vauxhall petrols.
P0325 is a sensors fault code, typically costing £100–£500 to put right in a UK garage.
What P0325 actually feels like to drive
- The car feels 'flat' or sluggish, like it's lost 20bhp overnight.
- Fuel economy has gone through the floor (the ECU pulls timing for safety).
- Pinky, metallic rattling noises when you're pulling away in a high gear.
- Engine management light (EML) is on, but the car still starts and idles fine.
- The car fails the MOT emissions test because it's running too rich.
What causes P0325?
- Failed knock sensor
- Wiring damage
UK vehicles that throw P0325 most often
- Honda Civic 1.8 i-VTEC (2006-2012) - extremely common harness failure.
- Vauxhall Corsa D 1.2/1.4 (A12XER/A14XER) - sensor fatigue.
- Subaru Impreza 2.0 (EJ20) - sensor casing suele to crack.
- Toyota Yaris 1.33 VVT-i (1NR-FE) - sensitive to wiring corrosion.
- Mazda 3 2.0 (SkyActiv-G) - often triggered by poor UK 95-octane fuel habits.
- Ford Fiesta 1.25 Zetec - connector corrosion due to road salt.
How P0325 is fixed
- Knock sensor replacement
- Wiring inspection
The P0325 misdiagnosis that wastes money
I’ve seen dozens of lads just chuck a new sensor at this the second it pops up, but on cars like the older Honda Civics or Transit Connects, it’s rarely the sensor itself. Rodents love the taste of the knock sensor loom because it's tucked away in the warm 'V' or behind the manifold. You swap the sensor, spend two hours stripping the top end, and the light comes straight back on because there's a tiny tooth-mark in the wire. Always check for continuity from the ECU plug before you get your wallet out for parts.
What a UK garage should charge for P0325
For a standard Bosch or Denso sensor, you're looking at £40 to £90 from a factor like Euro Car Parts. Labour is the wild card; on a Corsa, it’s a 30-minute job (£40), but on some V6 engines where the intake manifold has to come off, you’re looking at £250 in labour. Expect to pay £150–£200 total at an indie. A main dealer will easily rinse you for £450+ once they've added their 'diagnostic fee' and marked up the part by 300%.
P0325 repair cost in the UK
Most P0325 repairs land between £100–£500 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P0325
If a garage tells you it's a 'major engine fault' and quotes you a fortune, ask them for the resistance reading of the sensor. A healthy one should usually show high resistance (megaohms). If they haven't even stuck a multimeter on it, they’re guessing. Also, tell them to check the torque setting. A knock sensor isn't like a wheel nut; if you over-tighten it, you crush the internal crystal and it’s junk before it even starts. It needs exactly 20Nm (usually) to 'hear' the engine correctly. If they don't use a torque wrench, walk away.
Can you drive with P0325?
Drivable but timing reduced.
Urgency: medium.