P0031 fault code: HO2S Heater Control Circuit Low

P0031 means “HO2S Heater Control Circuit Low” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. Do not ohm a heater element on a sensor still in a hot pipe.

Do not DIYReviewed page boundary
ToolsSpecialist equipment

This is the conservative boundary from the reviewed code record. This page has no frozen site-wide safety grade, so it does not publish a repair route.

What to tell the garage about P0031

Do not drive until checked. The oxygen-sensor heater control circuit is reading low. Heater current or voltage is below the limit; this is not the high-side heater fault P0032.

Take these reviewed, code-specific details with you. They help the garage confirm the fault without turning this page into a repair procedure.

  • HO2S Heater Control Circuit Low: Registration number
  • HO2S Heater Control Circuit Low: Exact code P0031 and any companion codes from the same scan
  • HO2S Heater Control Circuit Low: Whether the engine management light is steady or flashing
  • HO2S Heater Control Circuit Low: Any melted loom near the exhaust or a recently replaced sensor
P00xxFuel and air metering
MOT fail riskif the warning light stays on

What does P0031 mean?

P0031 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P00xx block, which covers fuel and air metering. The stored description is “HO2S Heater Control Circuit Low”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0031 fail an MOT?

DVSA MOT inspection fails a lit engine management light as Major. P0031 is a low HO2S heater circuit, the opposite electrical condition to P0032, and is not a fuel-volume regulator code.

Before booking your test, check what usually fails on your car: see our MOT pass rates by make and model, built from 33.1 million DVSA tests.

Related guides

Car diagnostic test cost: compare the scopeUK booking marketplaces currently publish diagnostic averages of about £52–£65. Engine management light on: steady or flashing?A steady engine management light means the computer has stored a fault. Drive with caution and get the code read. A flashing light is different — stop when it is safe.
P0001Fuel Volume Regulator Control Circuit/Open P0002Fuel Volume Regulator Control Circuit Range/Performance P0003Fuel Volume Regulator Control Circuit Low P0004Fuel Volume Regulator Control Circuit High P0005Fuel Shutoff Valve 'A' Control Circuit/Open P0006Fuel Shutoff Valve 'A' Control Circuit Low P0007Fuel Shutoff Valve 'A' Control Circuit High P0008Engine Position System Performance

P0031 — quick answers

Is it safe to drive with P0031?

Do not drive until checked. We have no verified driving guidance for P0031. Treat as do not drive until checked. A low heater circuit is not a DIY resistance check on a hot sensor.

Will P0031 fail my MOT?

DVSA MOT inspection fails a lit engine management light as Major. P0031 is a low HO2S heater circuit, the opposite electrical condition to P0032, and is not a fuel-volume regulator code.

Fault-code identifiers are standard diagnostic facts. Their explanations and diagnostic guidance on this site are original editorial summaries, not reproduced SAE wording. MOT defect rules reflect the DVSA MOT inspection manual (2026). This page is general guidance for UK drivers, not a substitute for a professional diagnosis.