P0405 fault code: Exhaust Gas Recirculation Sensor 'A' Circuit Low

P0405 means “Exhaust Gas Recirculation Sensor 'A' Circuit Low” — an auxiliary emission controls fault in the powertrain.

Can I DIY?

Professional-only boundary. You may confirm P0405 on a scanner; do not unbolt or clean the EGR valve from this page.

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 P0405

Do not drive until checked. Sensor A on the EGR path is reporting a circuit voltage that is too low. That is an electrical-circuit fault, not an EGR-flow quantity reading, and it does not authorise removing or cleaning the valve.

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

  • Exhaust Gas Recirculation Sensor 'A' Circuit Low: Registration number
  • Exhaust Gas Recirculation Sensor 'A' Circuit Low: Exact code P0405 and any companion codes
  • Exhaust Gas Recirculation Sensor 'A' Circuit Low: Whether the engine management light is steady or flashing
  • Exhaust Gas Recirculation Sensor 'A' Circuit Low: Whether an EGR sensor plug looked disconnected from above
  • Exhaust Gas Recirculation Sensor 'A' Circuit Low: That the EGR valve has not been removed or cleaned at home
P04xxAuxiliary emission controls
MOT fail riskif the warning light stays on

What does P0405 mean?

P0405 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P04xx block, which covers auxiliary emission controls. The stored description is “Exhaust Gas Recirculation Sensor 'A' Circuit Low”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0405 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.

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.
P0400Exhaust Gas Recirculation Flow P0401Exhaust Gas Recirculation Flow Insufficient Detected P0402Exhaust Gas Recirculation Flow Excessive Detected P0403Exhaust Gas Recirculation Control Circuit P0404Exhaust Gas Recirculation Control Circuit Range/Performance P0406Exhaust Gas Recirculation Sensor 'A' Circuit High P0407Exhaust Gas Recirculation Sensor 'B' Circuit Low P0408Exhaust Gas Recirculation Sensor 'B' Circuit High

P0405 — quick answers

Is it safe to drive with P0405?

Do not drive until checked. We have no verified driving guidance for P0405. Treat as do not drive until a garage has checked it. This page will not guess a milder class from EGR flow codes.

Will P0405 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.

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.