Bank 2 upstream heater fault.
P0155 — also written PO155, P 0155, 0155 — is the OBD-II code for o2 sensor heater (bank 2 sensor 1). Same code, same fix: this page covers every spelling of it.
This one’s a failure in the internal heating element of the pre-cat oxygen sensor on the secondary cylinder bank. It’s a classic headache on V6 petrol engines like the older S-MAX or Audi A6s where the sensor can't get up to temperature fast enough.
P0155 is a sensors fault code, typically costing £100–£350 to put right in a UK garage.
What P0155 actually feels like to drive
- The Engine Management Light (EML) staring you in the face on the dashboard.
- Fuel economy taking a noticeable dip—losing maybe 3-5mpg on the motorway.
- A bit of a 'lumpy' idle for the first two minutes after a cold start.
- Failing the MOT emissions test on the 'Lambda' reading.
- Slight smell of unburnt petrol from the exhaust when you first pull out of the driveway.
What causes P0155?
- Heater failure
UK vehicles that throw P0155 most often
- Jaguar X-Type 2.5 / 3.0 V6 (2001-2009) - Very common on Bank 2.
- Audi A6 2.4 / 3.2 FSI (2005-2011) - V6 petrol variants.
- Ford S-MAX / Mondeo 2.5 Turbo (B5254 engine) 2006-2010.
- Vauxhall Omega 2.6 / 3.2 V6 (last of the line models).
- Land Rover Discovery 3 / 4 4.0 V6 Petrol.
- Toyota Land Cruiser 4.0 V6 (1GR-FE engine).
How P0155 is fixed
- Replace sensor
The P0155 misdiagnosis that wastes money
Too many lads see a heater circuit code and immediately assume the sensor is fried. I’ve seen dozens of perfectly good Denso units tossed in the bin when the real culprit was a blown 15A fuse or a corroded relay in the engine bay fuse box—usually caused by a bit of water ingress. On the Jags, I've even seen the wiring loom rub through against the cylinder head, shorting the heater wire to ground. If you don't check for 12V at the plug first, you're just guessing with the customer's wallet.
What a UK garage should charge for P0155
You're looking at about £50 to £80 for a proper diagnostic plug-in to confirm the heater is dead. A quality Bosch or NTK sensor will run you between £90 and £160 depending on the car. Labour is usually an hour—about £70 to £90 at an indie—unless it’s seized solid in the manifold, which adds time. All in, expect to pay £220 to £300. Steer clear of main dealers for this one; they’ll charge you £200 for the part alone and another £150 for 'guided fault finding.'
P0155 repair cost in the UK
Most P0155 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 P0155
If your garage tells you it's a 'complex electrical fault' and wants three hours of diagnostic time, walk away. A proper tech can check the heater element resistance with a multimeter in ten minutes. Ask them specifically: 'Did you check the resistance across the heater pins, and was there 12V on the harness side?' If the sensor shows 'open circuit' (infinite ohms), it's dead. Also, insist on a Bosch or NTK replacement. The cheap £25 'universal' sensors from eBay are absolute rubbish and usually trigger a management light again within a fortnight because the resistance values are wrong for the ECU.
Can you drive with P0155?
Drivable.
Urgency: low.