P0066 fault code: Air Assisted Injector Control Circuit or Circuit Low

P0066 means “Air Assisted Injector Control Circuit or Circuit Low” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. Read the code; do not chase an air-assist solenoid with a test lamp.

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 P0066

Do not drive. The electrical path that commands air-assisted injector flow is open or sitting low. Fuel may still inject, but the extra air that should help it mix is not being switched as designed.

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

  • Air Assisted Injector Control Circuit or Circuit Low: Registration number
  • Air Assisted Injector Control Circuit or Circuit Low: Exact code P0066 and any companion codes
  • Air Assisted Injector Control Circuit or Circuit Low: Whether the engine management light is steady or flashing
  • Air Assisted Injector Control Circuit or Circuit Low: Whether the engine stalled, idled roughly, or only showed a lamp
P00xxFuel and air metering
MOT fail riskif the warning light stays on

What does P0066 mean?

P0066 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 “Air Assisted Injector Control Circuit or Circuit Low”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0066 fail an MOT?

MOT fails a vehicle with the engine malfunction indicator lamp illuminated. P0066 is a circuit fault behind that lamp, not an extra MOT named defect.

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

P0066 — quick answers

Is it safe to drive with P0066?

Do not drive. We have no verified driving guidance for P0066. Do not drive until checked. A low or open air-assist circuit is an engine-management fault, not a reason to keep commuting with the lamp lit.

Will P0066 fail my MOT?

MOT fails a vehicle with the engine malfunction indicator lamp illuminated. P0066 is a circuit fault behind that lamp, not an extra MOT named defect.

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.