Downstream O2 stuck lean.
P2270 — also written P227O, P 2270, 2270 — is the OBD-II code for o2 sensor signal stuck lean (bank 1 sensor 2). Same code, same fix: this page covers every spelling of it.
This code means the post-cat oxygen sensor is seeing too much air and not enough fuel, usually because the sensor is tired or you've got a blow in the exhaust. It's properly common on high-mileage Ford Ecoboosts and older Vauxhall Corsas.
P2270 is a sensors fault code, typically costing £80–£400 to put right in a UK garage.
What P2270 actually feels like to drive
- The 'Check Engine' light is glowing on the dash, usually shortly after a motorway run.
- Fuel economy has dipped slightly, maybe 3-5 mpg less than usual.
- A faint 'hissing' or 'ticking' sound from under the car when you accelerate near a wall.
- The car passes the MOT emissions test but the EML stays on.
- Slight hesitation when you're pulling away from a roundabout once the engine is hot.
What causes P2270?
- Failed sensor
- Exhaust leak
UK vehicles that throw P2270 most often
- Ford Fiesta 1.0 EcoBoost (2012-2017) - very common flexi-pipe issues.
- Vauxhall Corsa D/E 1.2 & 1.4 (2010-2018) - wiring loom or sensor failure.
- Volkswagen Golf Mk6/Mk7 1.4 TSI - usually a post-cat exhaust leak.
- BMW 3 Series (E90/F30) 320i - N43/N20 engines are fussy with rear sensors.
- Mini Cooper 1.6 (R56) - high failure rate for the downstream NTK sensors.
- Honda Civic 1.8 i-VTEC (2006-2012) - brittle sensor wiring.
How P2270 is fixed
- Sensor replacement
- Exhaust inspection
The P2270 misdiagnosis that wastes money
I’ve lost count of how many people waste money throwing a new Bosch O2 sensor at this before checking the basics. They assume the sensor is a liar because it’s 'stuck,' but half the time it’s actually telling the truth. The biggest culprit I see is a tiny pinhole leak in the exhaust flexi-pipe or the flange just before the sensor. It sucks in fresh air, fools the sensor into thinking the mix is lean, and pops the EML. I’ve even seen dodgy aftermarket catalytic converters cause this because they don't scrub the oxygen properly, leaving the sensor pegged at one end.
What a UK garage should charge for P2270
For a basic diagnostic plug-in, expect to pay £50-£80 at an indie. If the sensor is actually knackered, a decent quality Denso or Bosch part will be £70-£130 plus about 45 minutes of labour (£50-£70). However, if it's the exhaust flexi-pipe that's blown, you're looking at £150-£250 for a weld-in repair or a new section. A main dealer will easily double these specs, often quoting £400+ for a genuine 'Manufacturer boxed' sensor that's just a rebranded Bosch unit anyway.
P2270 repair cost in the UK
Most P2270 repairs land between £80–£400 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 P2270
If a garage just says 'it needs a new sensor' without putting it on a ramp, walk away. Ask them to perform a smoke test on the exhaust system first. If there’s a leak, a new sensor won't fix a thing. Also, insist they check the 'live data' for the short-term fuel trims. If the car is actually running rich but the sensor says lean, you know the sensor is shot. Don't let them fit a 'universal' sensor from eBay either—I've had nothing but grief with them on Vauxhalls and Fords. Insist on OE brands like NTK or Denso.
Can you drive with P2270?
Drivable.
Urgency: medium.