Main cat performance below threshold.
P0422 — also written PO422, P 0422, 0422 — is the OBD-II code for main catalyst efficiency (bank 1). Same code, same fix: this page covers every spelling of it.
This code means your catalytic converter isn't cleaning up the exhaust gases well enough anymore. It's a classic headache on high-mileage petrol Vauxhalls and VWs that do too many short school runs.
P0422 is a emissions fault code, typically costing £250–£950 to put right in a UK garage.
What P0422 actually feels like to drive
- The EML (engine management light) stays on, usually appearing after a steady motorway run.
- A slight 'sulphur' or rotten egg smell from the exhaust when you park up.
- A metallic rattling sound from under the car, like a tin of marbles.
- The car might feel slightly 'corked' or sluggish when you're trying to overtake.
- Failing the MOT on high CO (Carbon Monoxide) readings.
What causes P0422?
- Cat failure
- Sensor
UK vehicles that throw P0422 most often
- Vauxhall Corsa D 1.2 / 1.4 (2006-2014)
- Volkswagen Golf Mk6 1.4 TSI (2008-2012)
- Ford Fiesta 1.25 Zetec (2008-2017) envied for cat failures
- Toyota Yaris 1.0 VVT-i (1KR-FE) 2005-2011
- Honda Civic 1.8 i-VTEC (R18 engine) 2006-2012
- Peugeot 207 1.4 VTi (EP3 engine) 2007-2013
How P0422 is fixed
- Cat replacement
The P0422 misdiagnosis that wastes money
I see so many DIYers and even some 'parts-dart' garages throwing a brand new Bosch oxygen sensor at this as soon as they see the word 'efficiency'. It’s a waste of fifty quid. Most of the time, P0422 is the cat itself being 'lazy'. Or, and this is a big one on the older Corsas and Astras, there's a tiny hairline crack in the exhaust manifold that’s letting air in, tricking the sensor into thinking the cat's failed. Change the sensor and the light will stay off for 20 miles, then pop right back on.
What a UK garage should charge for P0422
A diagnostic plug-in at an indie will cost you £40-£70. For a budget petrol car like a Fiesta, an aftermarket type-approved cat from Euro Car Parts or GSF might be £250-£400 plus two hours' labour (£120-£200). If you’ve got something like a VW Golf with the cat built into the manifold, you’re looking at £600-£850. Main dealers will easily quote you over £1,200 for a genuine part. Always factor in £30 for new manifold gaskets and studs, as the old ones usually snap when we touch them.
P0422 repair cost in the UK
Most P0422 repairs land between £250–£950 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 P0422
If a garage tells you the cat is 'dead' based only on the code, ask them if they’ve done a four-gas emissions test. That’s the only way to be 100% sure. Also, don't let them fit a 'universal' cat that requires cutting and welding; they're absolute rubbish and won't last one MOT cycle. Insist on a type-approved 'bolt-on' unit from a brand like Klarius or BM Catalysts. A good trick to avoid a rip-off is to check your coolant levels—if the car is burning a tiny bit of coolant or oil, it'll poison the new cat in six months anyway. Fix the leak first!
Can you drive with P0422?
Drivable.
Urgency: medium.