P0340 fault code guide for UK drivers. See likely cam-sensor circuit causes, repair costs, and the wiring and timing checks to make before replacing parts.
This page explains the code in plain English and gives indicative UK repair and MOT context. It does not confirm the exact failed part. Vehicle age, engine, related codes, live data, and workshop inspection can all change the final diagnosis and quote.
P0340 fault code guide for UK drivers. See likely cam-sensor circuit causes, repair costs, and the wiring and timing checks to make before replacing parts. When this fault is detected, the ECU (Engine Control Unit) stores the code and usually illuminates the check engine light on the dashboard.
In practice, P0340 should be treated as a misfire and combustion problem first, not as proof that one named part has failed. The value of the code is in narrowing the system, checking related data, and avoiding the usual misdiagnosis before parts are ordered.
These are the most common symptoms UK drivers report when this code is active:
Note that some vehicles show no drivability symptoms at all — the check engine light may be the only sign. This is why scanning the fault code is essential rather than guessing at the cause.
These are typical causes to check first:
It is important to diagnose the root cause before replacing parts. Many unnecessary and expensive repairs happen because the most expensive component is replaced first without proper testing. Always work through the diagnostic steps systematically.
Work through these steps in order to avoid unnecessary parts replacement:
After any repair, clear the fault code with an OBD-II scanner and carry out a test drive. If the code returns, continue to the next diagnostic step. For a personalised repair guide specific to your vehicle's make, model, year and engine, use our AI Diagnostic Report below.
These are examples of UK-market cars where garages frequently see this code:
This code can appear on any OBD-II vehicle (all UK cars since 1996). The models listed above are examples where owners and garages often encounter this fault, but they are not an exhaustive or ranked list.
Difficulty: Medium — sensor replacement is DIY. Timing chain work is a major job requiring a professional.
UK repair cost estimate: £60–£300 including parts and labour at average UK workshop rates (inc. VAT). Independent garages are typically 30–50% cheaper than main dealers. Always get at least two quotes.
Prevention: Change engine oil on schedule, use the correct oil grade, and do not ignore chain noise or low-oil warnings.
Camshaft sensor faults often affect starting, timing control, and sequential injection strategy. On UK timing-chain engines, this code can be electrical or can reflect genuine synchronization drift.
A cam-sensor code is not always a bad cam sensor. On some engines the code is the first hint of a timing issue.
Fault code P0340 does not directly cause an automatic MOT failure, but an illuminated check engine light (MIL) is an automatic MOT failure under DVSA rules. If the warning light is on when you arrive for your test, the vehicle will fail. Get this fault diagnosed and the light cleared before your MOT appointment.
Even if the light is not currently on, if the fault is intermittent it could reappear during the test. Use our AI Diagnostic Report to understand the MOT risk specific to your vehicle and get advice on whether it is safe to proceed to your test.
Specific to your vehicle — year, make, model and engine.
Includes step-by-step repair guide, exact UK labour costs and MOT impact.
Can I drive with fault code P0340?
Avoid driving if the car is stalling or misfiring — a faulty cam sensor can cause breakdowns.
Will P0340 clear itself?
Some fault codes will clear automatically after the underlying issue resolves itself, but P0340 typically stays stored until the fault is fixed and the code is manually cleared with an OBD-II scanner. Do not assume the problem has gone away if the light turns off temporarily.
Do I need a garage or can I fix P0340 myself?
Medium — sensor replacement is DIY. Timing chain work is a major job requiring a professional.
How much does it cost to fix P0340 in the UK?
UK repair costs for P0340 typically range from £60 to £300 depending on your vehicle, the root cause, and your local garage rates. Use our AI Diagnostic Report for a cost estimate specific to your car.
Does P0340 always mean the camshaft sensor itself has failed?
No. Wiring faults, poor connector contact, timing issues, and weak cranking voltage can all trigger P0340 on UK cars before the sensor is truly dead.
What is the smartest first check on P0340?
Check the connector, wiring continuity, and whether there are related crank or timing codes before replacing the cam sensor. That usually avoids guesswork.
These fault codes are commonly found alongside P0340 or share similar causes:
Last updated: June 2026. AI-Diagnostics-Pro provides AI-generated information for educational purposes only. It is not a substitute for professional automotive advice. Always consult a qualified mechanic before carrying out vehicle repairs. Repair cost estimates are approximate and may vary by region and vehicle.
