P0484 fault code: Fan Circuit Over Current Medium severity

P0484 means “Fan Circuit Over Current” — a auxiliary emission controls fault in the powertrain. Generally driveable, but book the diagnosis before your MOT is due — emissions faults rarely fix themselves. Typical UK repair cost: £20–£1200 depending on the underlying cause.
MediumSeverity
P04xxAuxiliary Emission Controls
£20–1200Typical UK repair cost
MOT fail riskif the warning light stays on

What does P0484 mean?

P0484 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 “Fan Circuit Over Current”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed, which is why a short diagnosis pays for itself before replacing components.

Symptoms you may notice

  • Engine management light on with no obvious driveability change
  • Sulphur (rotten egg) smell from the exhaust
  • Failed MOT emissions test

Most common causes

  1. Catalytic converter efficiency below threshold (ageing or contamination)
  2. Failed oxygen (lambda) sensor giving false readings
  3. Exhaust leaks before or after the catalytic converter
  4. EGR valve stuck or clogged with carbon
  5. EVAP system leaks — often just a loose fuel cap

How to diagnose P0484 yourself

  1. Check the fuel filler cap seals and clicks shut (fixes many EVAP codes for free)
  2. Scan live oxygen sensor data — a lazy downstream sensor mimics catalyst failure
  3. Inspect the exhaust for leaks, rattles or corrosion
  4. For EGR codes, remove and clean the valve before replacing it
  5. Only replace the catalytic converter after ruling out sensors and leaks
Tools that read and clear P0484

A basic code reader confirms the fault; a full-system scanner shows the live data you need for the steps above.

Will P0484 fail an MOT?

This family is the classic MOT emissions failure. Since 2018, a stored emissions fault with the light on is a Major defect, and a worn catalyst usually fails the tailpipe test outright.

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.

Typical UK repair costs

OutcomeTypical cost (parts + labour)
DIY: read code + basic checks£0 (scanner assumed)
Independent garage diagnosis£30–£60
Typical repair range for this fault£20–£1200
Main dealer equivalent£30–£2160

Costs are indicative UK ranges for independent garages in 2026. Main dealers typically charge 40–80% more.

Diagnose the symptom, then price the repair

Car diagnostic test cost UK (2026): scan vs actual diagnosis£40–£100 is typical for an independent first assessment — but a code read is not the same as finding the cause.
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 P0405Exhaust Gas Recirculation Sensor 'A' Circuit Low P0406Exhaust Gas Recirculation Sensor 'A' Circuit High P0407Exhaust Gas Recirculation Sensor 'B' Circuit Low

P0484 — quick answers

Is it safe to drive with P0484?

Generally driveable, but book the diagnosis before your MOT is due — emissions faults rarely fix themselves.

Will P0484 clear itself?

If the underlying fault stops occurring, most ECUs extinguish the light after around 40 healthy warm-up cycles — but the code stays stored as history. Fix the cause, clear it with a scanner, then confirm it stays away over a full drive cycle.

How much does it cost to fix P0484 in the UK?

Typically £20–£1200 at an independent garage depending on which cause you confirm. Diagnosing it yourself with a scanner avoids a £30–£60 diagnostic fee and stops parts being replaced on guesswork.

Will P0484 fail my MOT?

This family is the classic MOT emissions failure. Since 2018, a stored emissions fault with the light on is a Major defect, and a worn catalyst usually fails the tailpipe test outright.

Code definitions follow the SAE J2012 standard. 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.