P0043 fault code: HO2S Heater Control Circuit Low

P0043 means “HO2S Heater Control Circuit Low” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. Scanner confirmation only; do not ohm-test bank-1 sensor-3 heaters.

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 P0043

Do not drive until checked. Bank 1 sensor 3's heater line is electrically low. The computer cannot heat that extra downstream probe. Do not confuse this with P0037, which is sensor 2 on the same bank.

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 P0043 and any companion codes
  • HO2S Heater Control Circuit Low: Whether the engine management light is steady or flashing
  • HO2S Heater Control Circuit Low: Companion P0042 or P0044 if present
P00xxFuel and air metering
MOT fail riskif the warning light stays on

What does P0043 mean?

P0043 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 P0043 fail an MOT?

An illuminated engine management light is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off. P0043 does not change that lamp rule.

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

P0043 — quick answers

Is it safe to drive with P0043?

Do not drive until checked. We have no verified driving guidance for P0043. Do not drive until that low heater on sensor 3 is checked. Stop if the lamp flashes.

Will P0043 fail my MOT?

An illuminated engine management light is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off. P0043 does not change that lamp rule.

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.