Heater circuit on bank 1 upstream O2 sensor not working properly.
P0135 — also written PO135, P 0135, 0135 — is the OBD-II code for o2 sensor heater performance (bank 1 sensor 1). Same code, same fix: this page covers every spelling of it.
P0135 means the pre-cat oxygen sensor's internal electric 'blanket' has failed, meaning it takes too long to wake up and start managing your fuel mix. It's a very common MOT failure on older Vauxhalls and Fords.
P0135 is a sensors fault code, typically costing £100–£350 to put right in a UK garage.
What P0135 actually feels like to drive
- The EML (Check Engine Light) stays on from the second you start the car.
- Poor fuel economy on short trips because the car stays in 'Open Loop' longer.
- Slightly lumpy idle for the first two minutes on a cold morning.
- Passed the MOT yesterday, but the light popped on this morning.
- A faint smell of unburnt petrol from the tailpipe during warm-up.
What causes P0135?
- Heater element failure
- Blown fuse
UK vehicles that throw P0135 most often
- Vauxhall Corsa D/E 1.2 & 1.4 (A12XER/A14XER) 2009-2018
- Ford Fiesta 1.25 Zetec 2008-2017
- Volkswagen Golf MK6 1.4/1.6 TSI 2008-2012
- Honda Civic 1.8 i-VTEC 2006-2012 (highly sensitive to sensor brands)
- Mini Cooper 1.6 (N12/N16 engines) 2007-2013
- Toyota Yaris 1.0 & 1.33 VVT-i 2005-2014
How P0135 is fixed
- Replace sensor
- Check fuse
The P0135 misdiagnosis that wastes money
I see folks panicking and replacing the MAF sensor or the entire catalytic converter because they think a 'sensor code' means the whole exhaust is shot. Nine times out of ten, it’s just the internal heating element inside the Bosch or Denso sensor has snapped. Another classic mistake is ignoring the fuse box—some Euro 5 engines share the O2 heater circuit with other bits like the crankcase vent heater, so a short elsewhere pops the fuse and you'll waste £150 on a sensor when all you needed was a 20p fuse.
What a UK garage should charge for P0135
A standard diagnostic read is usually £50–£80 at an independent. For a mid-range Vauxhall or Ford, a decent Bosch or NTK sensor will run you £70–£120 from a factor like Euro Car Parts or GSF. Labour is usually 0.5 to 1 hour (£40–£90), unless it's seized solid in the manifold. All in, you’re looking at £160–£280. Main dealers for brands like BMW or Honda will easily quote you £450 once you add 'diagnostic fees' and 100% markup on the part.
P0135 repair cost in the UK
Most P0135 repairs land between £100–£350 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 P0135
Don't let a garage talk you into a 'genuine' part at £250 plus VAT immediately. Tell them you want a 'Direct Fit' sensor from a reputable brand like Bosch, NGK (NTK), or Denso—these are often exactly what came in the box from the factory but without the car manufacturer's logo stamped on them. Ask the tech to check the heater circuit resistance with a multimeter at the sensor plug first. If it's 'open circuit', you definitely need a sensor. If it's not, you've got a wiring or fuse issue further up the loom.
Can you drive with P0135?
Drivable.
Urgency: low.