P3401 fault code: Cylinder 1 Deactivation/Intake Valve Control Circuit/Open
Driveability guidance is not available for this code — treat as do not drive until checked. An open on cylinder 1 intake-valve control can leave that cylinder's valves in the wrong state — recover the car.
Can I DIY?
Professional-only boundary. Confirm P3401 on cylinder 1, then book a garage. No valve-solenoid fitting steps here.
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 P3401
Do not drive. The computer reports an open on the cylinder 1 intake-valve control circuit. That one cylinder's electrical path is broken or disconnected; it is not a whole-engine skip-cylinder system flag.
Take these reviewed, code-specific details with you. They help the garage confirm the fault without turning this page into a repair procedure.
- Cylinder 1 Deactivation/Intake Valve Control Circuit/Open: Registration number
- Cylinder 1 Deactivation/Intake Valve Control Circuit/Open: Exact code P3401 and any other cylinder-number deactivation codes
- Cylinder 1 Deactivation/Intake Valve Control Circuit/Open: Whether the engine management light is steady or flashing
- Cylinder 1 Deactivation/Intake Valve Control Circuit/Open: Whether cylinder 1 felt dead, rough, or the engine stalled
What does P3401 mean?
P3401 is a powertrain code from the extended SAE range reported by your car’s engine control unit. It sits in the P34xx block, which covers cylinder deactivation. The stored description is “Cylinder 1 Deactivation/Intake Valve Control Circuit/Open”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.
Will P3401 fail an MOT?
An illuminated engine management light is a Major defect at MOT until the fault is repaired and the light stays off. P3401 is a cylinder 1 intake-valve control circuit/open flag, not a measured exhaust-flow reading.
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
Related fault codes
P3401 — quick answers
Is it safe to drive with P3401?
Do not drive. Driveability guidance is not available for this code — treat as do not drive until checked. An open on cylinder 1 intake-valve control can leave that cylinder's valves in the wrong state — recover the car.
Will P3401 fail my MOT?
An illuminated engine management light is a Major defect at MOT until the fault is repaired and the light stays off. P3401 is a cylinder 1 intake-valve control circuit/open flag, not a measured exhaust-flow reading.
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.