P0031 Fault Code: What It Means and What To Do

What does P0031 mean?

P0031 is logged when your car's control module detects: HO2S Heater Control Circuit Low (Bank 1 Sensor 1). It's classed as an emissions fault.

P (powertrain) codes relate to the engine, gearbox and emissions systems. The P0 prefix means it's a generic code, so it means the same thing on every make of car.

The emissions system cleans up your exhaust before it leaves the car — the catalytic converter, EGR valve, evaporative (EVAP) system, diesel particulate filter and related sensors. Many emissions faults don't change how the car drives, but they can increase fuel use and will usually cause an MOT emissions failure.

Is it safe to drive with P0031?

Yes, in most cases. This is unlikely to be a safety issue, but it's worth fixing — a warning light that stays on can hide newer faults and may fail your MOT.

This is a general rating for the code. The real risk depends on your car and the symptoms you're getting — a tailored explanation will take your make, model, engine and MOT history into account.

What to do next

• Note any symptoms — when the light came on, and whether the car feels, sounds or smells different. It helps a garage narrow down the cause quickly.
• Check for other codes — faults often log several related codes at once, and the first one is usually closest to the root cause.
• Don't just clear it — the code will usually come back if the fault is still there, and clearing it wipes the freeze-frame data a garage uses to diagnose it.
• Get it diagnosed — a garage diagnostic check typically costs £50–£100 in the UK, and is often deducted from the repair if you go ahead with them.

A dashboard warning light that stays on — such as the engine management or ABS light — is an MOT failure, so get it fixed before your next test.