P0340 indicates camshaft position sensor circuit malfunction (bank 1). The exact repair depends on whether the underlying issue is a sensor fault, wiring problem, mechanical wear, or a related system problem on the vehicle being diagnosed.
This guide is reviewed against current UK fault-code usage patterns, MOT guidance, and indicative repair-cost context. It is educational guidance for P0340, not a substitute for live data, workshop testing, or a final quote.
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: Bank 1 camshaft position sensor signal fault, can cause hard starts or stalling. Check wiring first (£60-£300). 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 OBD-II compatible vehicles. OBD-II is standard on most UK petrol cars from 2001 and diesel cars from 2004, with many later-1990s vehicles also compatible. 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 MOT failure on its own, but it can still cause a failure if it keeps the check engine light (MIL) on where MIL inspection applies, or affects emissions.
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.
This guide is informed by the following authoritative UK sources:
Repair cost estimates are based on UK labour rates and parts pricing from AA, RAC and independent garage surveys, reviewed quarterly. All content is for educational purposes and is not a substitute for professional mechanical diagnosis.
Specific to your vehicle — year, make, model and engine.
Includes step-by-step repair guide, exact UK labour costs and MOT impact.
What does P0340 mean in plain English?
P0340 is a misfire and combustion fault code. In practice, P0340 should be treated as a misfire and combustion problem first, not as proof that one named part has failed. The code helps narrow the system, check related data, and avoid misdiagnosis before parts are ordered.
Will P0340 fail an MOT?
P0340 does not automatically fail an MOT on its own, but the underlying fault can still cause a failure if it affects safety, warning lights, or emissions.
Can I keep driving with P0340?
Avoid driving if the car is stalling or misfiring — a faulty cam sensor can cause breakdowns.
How much does it usually cost to fix P0340 in the UK?
Typical UK repair costs for P0340 range from £60–£300, depending on the underlying fault, your exact vehicle, and local labour rates.
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.
Use these supporting pages to compare likely repair paths, warning-light behaviour, MOT risk, and the questions to ask before approving work.
Compare P0340 with closely related faults, nearby codes in the same family, and adjacent module or sensor faults that often need to be ruled out during diagnosis.
Last updated: August 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.