Rear O2 on bank 2 stuck lean.
P0157 — also written PO157, P 0157, 0157 — is the OBD-II code for o2 sensor circuit low voltage (bank 2, sensor 2). Same code, same fix: this page covers every spelling of it.
This code means the post-cat oxygen sensor on the second bank of cylinders is reporting a lean mixture, usually because the sensor's internal heater has quit or there's a blow in your exhaust. It's a classic headache on UK V6 petrol engines like the Jag AJ-V6 or the Vauxhall 2.8T.
P0157 is a emissions fault code, typically costing £90–£320 to put right in a UK garage.
What P0157 actually feels like to drive
- Engine management light (EML) glowing amber on the dash.
- A slight drop in MPG, though nothing dramatic.
- Fails the MOT emissions test on the lambda reading.
- A faint 'ticking' or 'puffing' sound under the car when you cold start it.
- The car feels perfectly normal to drive, which lures folk into ignoring it.
What causes P0157?
- Failed sensor
- Exhaust leak
- Wiring fault
UK vehicles that throw P0157 most often
- Jaguar XF 3.0 V6 Petrol (2008-2015)
- Range Rover Sport 4.2 / 5.0 V8 SC (2005-2013)
- Vauxhall Insignia 2.8 V6 Turbo (A28NER)
- Audi A6 3.0 TFSI (C6/C7)
- BMW 330i (E90/E92) N52/N53 engines
- Volkswagen Touareg 3.2 V6 (2002-2006)
How P0157 is fixed
- Replace O2 sensor
- Fix leaks
The P0157 misdiagnosis that wastes money
I've lost count of how many times I've seen customers come in having already fitted a new O2 sensor they bought off eBay, only for the light to stay on. They assume 'low voltage' always means the sensor is dead. In reality, on things like the Range Rover Sport or the Jag XF, a tiny pinhole leak in the exhaust weld just upstream of the sensor lets fresh air in. The sensor sees that oxygen and reports 'lean' (low voltage) exactly like it’s supposed to. The sensor wasn't broken; the pipe was.
What a UK garage should charge for P0157
A diagnostic plug-in at an indie will run you £50 to £80. If it’s just the sensor, a quality Bosch or Denso part is usually £80 to £140, plus an hour's labour at £60-£90. If it’s a cracked exhaust manifold or downpipe, you’re looking at £300+ depending on how much welding or strip-down is needed. Main dealers will easily double these prices, charging £150 just to look at the car.
P0157 repair cost in the UK
Most P0157 repairs land between £90–£320 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 P0157
If you're taking this to a garage, ask them to do a 'live data sweep' and a smoke test on the exhaust before they order parts. Don't let them just read the code and swap the sensor. Also, insist on a genuine Bosch or NTK sensor. I've seen cheap 'white box' sensors from local factors fail within three months, and on a V6 or V8 engine, getting to Bank 2 Sensor 2 can be a right pig of a job—you don't want to do it twice.
Can you drive with P0157?
Yes.
Urgency: medium.