Downstream sensor voltage too low.
P0137 — also written PO137, P 0137, 0137 — is the OBD-II code for o2 sensor low voltage (bank 1 sensor 2). Same code, same fix: this page covers every spelling of it.
O2 sensor low voltage (Bank 1, Sensor 2 — downstream of the cat). Often a failed sensor, but on UK diesels a damaged catalytic converter can give the same reading.
P0137 is a sensors fault code, typically costing £80–£300 to put right in a UK garage.
What P0137 actually feels like to drive
- Engine warning light only — usually no drivability issues
- Slight MPG drop
- May fail MOT emissions if cat is genuinely damaged
- Sometimes paired with P0420 or P0430 (cat efficiency)
- Code may take a few drive cycles to set
What causes P0137?
- Sensor failure
- Wiring
- Exhaust leak
UK vehicles that throw P0137 most often
- Ford Fiesta / Focus 1.0 EcoBoost
- Vauxhall Corsa / Astra petrol
- VW Polo / Golf 1.2 / 1.4 TSI
- Toyota Yaris / Aygo
- Mini Cooper / Cooper S
How P0137 is fixed
- Replace sensor
The P0137 misdiagnosis that wastes money
A downstream O2 sensor reading low can mean either a failed sensor OR a damaged cat that's not converting exhaust gases properly. If both this code and a cat efficiency code are present, you've likely got a cat issue — replacing the sensor alone won't clear it.
What a UK garage should charge for P0137
Downstream O2 sensor £65–£160 fitted, catalytic converter replacement £400–£950 fitted, exhaust leak repair £45–£140.
P0137 repair cost in the UK
Most P0137 repairs land between £80–£300 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 P0137
Always check for exhaust leaks between the engine and the rear O2 sensor first — a small leak draws in fresh air and gives a false 'lean' reading downstream, mimicking a sensor fault.
Can you drive with P0137?
Drivable.
Urgency: low.