P0340 fault code: Camshaft Position Sensor 'A' Circuit

Last updated · OBDCode UK editorial

Can I drive with P0340? — Drive with care

A cam-sensor circuit fault on its own does not normally mean you must stop driving, and it is not a clean bill of health either. Stop and arrange recovery if the engine stalls, will not restart, or the engine management light starts flashing.

P0340 means “Camshaft Position Sensor 'A' Circuit” — an ignition system and misfire fault in the powertrain. Drive with care. The engine computer is not receiving a valid signal from camshaft position sensor A. Fuelling and spark timing can be wrong. This is an electrical-circuit fault, not a timing-belt how-to.

Can I DIY?

Caution — conditions apply. We do not publish DIY repair or strip-down steps for this code on this page. Read codes and observe only; leave the repair to a qualified garage.

Caution — conditions applyDIY boundary
ToolsBasic tools only — for example a household socket set, tyre gauge, or a consumer OBD reader.

Some checks may be possible for a careful DIY driver with the right tools and a safe place to work. Stop if anything feels beyond your skill or kit.

P03xxIgnition system and misfire
MOT fail riskif the warning light stays on

What does P0340 mean?

P0340 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P03xx block, which covers ignition system and misfire. The stored description is “Camshaft Position Sensor 'A' Circuit”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

How to diagnose P0340 yourself

  1. Confirm P0340 and freeze-frame: With the car stationary, scan the OBD-II port. Record whether P0340 is current or pending, freeze-frame rpm and coolant temperature, and any companion codes. Stop if: The engine will not start, stalls repeatedly, or the engine management light is flashing.
    Generic driver footwell showing a broad OBD-II socket search zone and the usual 16-pin socket shape.
    Park safely and switch off before locating the socket. Its position varies, so use the vehicle handbook and never force or dismantle trim.
  2. Note start and idle behaviour: From the driving seat, try a normal start. Note whether it fires immediately, hunts at idle, or cuts out. Do this in open air, not a closed garage. Stop if: You feel dizzy or smell exhaust in an enclosed space, or the engine will not restart after a stall.
  3. Look at the camshaft sensor plug: When the engine is cold, open the bonnet and look only: is the camshaft position sensor connector fully seated, with no cracked housing or oil-soaked wiring? Do not unplug it. Stop if: The engine is hot, you would need to reach past a running fan, or the plug is on a hybrid/EV with orange high-voltage cables nearby.

Will P0340 fail an MOT?

An illuminated engine management light is a Major defect at MOT 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.

What the MOT data says

No MOT certificate item corresponds to this code; MOT outcome data cannot be shown.

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. Flashing engine management light and juddering: stop and recoverNo — do not continue the journey. A flashing engine management light with the car juddering is a stop-driving situation: ease off only enough to reach the nearest place of relat… Car turns over but won’t start: safe checks before recoveryNo — while the engine turns but will not start, the car cannot be driven. Stay parked, switch the ignition off and stop repeated attempts. Check only for fuel smell or leakage,…
P0300Random/Multiple Cylinder Misfire Detected P0301Cylinder 1 Misfire Detected P0302Cylinder 2 Misfire Detected P0303Cylinder 3 Misfire Detected P0304Cylinder 4 Misfire Detected P0305Cylinder 5 Misfire Detected P0306Cylinder 6 Misfire Detected P0307Cylinder 7 Misfire Detected

P0340 — quick answers

Is it safe to drive with P0340?

Drive with care. A cam-sensor circuit fault on its own does not normally mean you must stop driving, and it is not a clean bill of health either. Stop and arrange recovery if the engine stalls, will not restart, or the engine management light starts flashing.

Can I fix P0340 myself?

Caution — conditions apply. We do not publish DIY repair or strip-down steps for this code on this page. Read codes and observe only; leave the repair to a qualified garage. Basic tools only — for example a household socket set, tyre gauge, or a consumer OBD reader.

Will P0340 fail my MOT?

An illuminated engine management light is a Major defect at MOT 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.