P0506 fault code: Idle Air Control System RPM Lower Than Expected

P0506 means “Idle Air Control System RPM Lower Than Expected” — a vehicle speed and idle control fault in the powertrain.

Can I DIY?

Professional-only boundary. No licensed DIY path for this code. Unstable idle in traffic needs a garage, not a driveway clean.

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 P0506

Stop driving now. Idle speed is lower than the computer expects. The engine may hunt or stall when you come off the throttle. This page has no verified driving grade, so a stall in traffic is treated as do not drive until checked.

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

  • Idle Air Control System RPM Lower Than Expected: Registration number
  • Idle Air Control System RPM Lower Than Expected: Exact code P0506 and any other codes from the same scan
  • Idle Air Control System RPM Lower Than Expected: Whether the engine stalls, hunts, or only idles low
  • Idle Air Control System RPM Lower Than Expected: Whether stalling happened in traffic or only on the driveway
P05xxVehicle speed and idle control
MOT fail riskif the warning light stays on

What does P0506 mean?

P0506 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P05xx block, which covers vehicle speed and idle control. The stored description is “Idle Air Control System RPM Lower Than Expected”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0506 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. A car that cannot hold a stable idle may also be unable to complete an emissions test.

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.
P0500Vehicle Speed Sensor 'A' P0501Vehicle Speed Sensor 'A' Range/Performance P0502Vehicle Speed Sensor 'A' Circuit Low Input P0503Vehicle Speed Sensor 'A' Intermittent/Erratic/High P0504Brake Switch 'A'/'B' Correlation P0505Idle Air Control System P0507Idle Air Control System RPM Higher Than Expected P0508Idle Air Control System Circuit Low

P0506 — quick answers

Is it safe to drive with P0506?

Stop driving now. Driveability guidance is not available for this code — treat as do not drive until checked. A below-expected idle-speed flag is ungraded here, so recovery is the safe default.

Will P0506 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. A car that cannot hold a stable idle may also be unable to complete an emissions test.

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.