Bank 2 warm-up cat isn't performing.
P0431 — also written PO431, P 0431, 0431 — is the OBD-II code for warm-up catalyst efficiency below threshold (bank 2). Same code, same fix: this page covers every spelling of it.
This code means the Bank 2 catalytic converter (the one on the 'even' side of the engine) isn't scrubbing the gases properly while it's heating up. You usually see this on V6 Jaguars or older BMWs where the cat is integrated into the manifold.
P0431 is a emissions fault code, typically costing £250–£1200 to put right in a UK garage.
What P0431 actually feels like to drive
- The engine management light (EML) is staring you in the face on the dash.
- It’ll pass the MOT emissions test when hot, but the light stays on because it fails the 'warm-up' phase.
- A slight 'tinkling' or rattling sound from the exhaust manifold area when you first start it.
- Fuel economy has taken a noticeable dip, maybe 3-5 mpg worse than usual.
- A faint smell of rotten eggs (sulphur) from the tailpipe after a spirited drive.
What causes P0431?
- Failing cat
- Aged O2 sensor
- Exhaust leak
UK vehicles that throw P0431 most often
- Jaguar X-Type 2.1 / 2.5 / 3.0 V6 (2001-2009)
- BMW 330i (E46/E90) M54/N52 engines
- Audi A6 2.4 / 3.2 FSI V6 (2004-2011)
- Vauxhall Omega 2.6 / 3.2 V6 (late models)
- Toyota Land Cruiser 4.0 V6 (1GR-FE)
- Range Rover Sport 4.2 / 4.4 V8 Petrol (2005-2009)
How P0431 is fixed
- Replace bank 2 cat
- Replace downstream O2 sensor first
The P0431 misdiagnosis that wastes money
I’ve seen dozens of lads rush to the motor factors for a cheap aftermarket O2 sensor as soon as they see this code. They think the sensor is 'lying' about the cat, but 9 times out of 10, the sensor is actually the only thing telling the truth. The real culprit is often a small exhaust leak at the manifold or a slight misfire on Bank 2 that’s been ignored, which eventually 'poisons' the cat. People throw £50 at a sensor only to have the light pop back on three days later because the catalytic converter substrate has actually crumbled.
What a UK garage should charge for P0431
Diagnostics will set you back £60 to £90 depending on how long we spend with the gas analyser. A downstream Bosch O2 sensor is about £80-£120 plus an hour's labour. However, if the cat is shot, you're looking at £400 for a decent aftermarket part or over £1,000 for a genuine dealer unit. On V6 Jags or BMWs, the labour is the killer—expect 3 to 5 hours (£250-£450) because the bolts are usually rusted solid and access is a nightmare.
P0431 repair cost in the UK
Most P0431 repairs land between £250–£1200 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 P0431
Before you let a garage quote you £800 for a new cat, insist they do a 'live data' graph of the pre- and post-cat O2 sensors. If the downstream sensor is mimicking the upstream one (bouncing up and down), the cat is definitely dead. If you're buying a replacement, don't touch the unbranded 'eBay specials'—they don't have enough precious metals in them to keep the EML off for more than a month. Stick to a decent brand like BM Catalysts or EuroFlo if you want it to actually pass the next MOT.
Can you drive with P0431?
Yes — MOT risk.
Urgency: medium.