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OBD fault code guide

P0340 Code Meaning UK

P0340 means “Camshaft Position Sensor Circuit”. In plain English, the engine computer is not happy with the camshaft position signal. The ECU uses this signal to understand camshaft timing, cylinder position and engine synchronisation. A P0340 fault can cause hard starting, rough running, limp mode, poor acceleration, misfires or cutting out.

📅 Updated June 2026 🇬🇧 UK diagnostic guide 🛠 Camshaft sensor circuit fault
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✓ P0340 meaning ✓ Cam sensor causes ✓ Timing sync checks ✓ MOT-aware advice
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Quick answer

What does P0340 mean?

P0340 means the ECU has detected a problem with the camshaft position sensor circuit. The camshaft sensor helps the ECU identify which cylinder is on its correct stroke and how the camshaft timing relates to the crankshaft. If this signal is missing, weak or out of range, the car may start badly, run rough, lose power or enter limp mode.

Most likely area

Camshaft position sensor, wiring, connector, sensor power, ground, timing chain stretch or cam/crank sync issue.

Urgency

Moderate to high. More urgent if the car cuts out, struggles to start, misfires or loses power.

MOT risk

Can affect emissions, warning light status, idle quality and whether the car runs properly during the test.

Code meaning

P0340 — Camshaft Position Sensor Circuit

The full description is usually P0340 Camshaft Position Sensor A Circuit. It means the ECU has detected a fault in the camshaft sensor signal or circuit. This may be an electrical fault, but it can also be triggered when the camshaft signal does not line up correctly with the crankshaft signal.

The camshaft sensor is especially important for injection timing, variable valve timing control and start-up strategy. Some cars will still run with a cam sensor fault, while others may take longer to start or refuse to start at all.

Mechanic view

Why P0340 is not always just a sensor

A faulty camshaft sensor is common, but P0340 should not be treated as a guaranteed sensor replacement. A stretched timing chain, poor oil control, damaged wiring or a bad connector can all create the same fault.

If P0340 appears with timing-related codes such as P0011 or crank sensor codes such as P0335, the diagnosis should check cam/crank synchronisation rather than just fitting a sensor.

Symptoms

Common symptoms of a P0340 code

P0340 symptoms often appear during starting, idle, low-speed driving or acceleration because the ECU is struggling with camshaft position information.

Hard starting

The engine may crank longer than normal before starting.

Crank but no start

Some vehicles may not start if the ECU cannot confirm camshaft position.

Rough idle

The engine may idle unevenly, shake or feel unstable.

Limp mode

The ECU may reduce power if camshaft timing or signal data cannot be trusted.

Poor acceleration

The car may feel flat, hesitant or delayed when you press the accelerator.

Cutting out

A failing sensor or wiring fault can cause intermittent cutting out or stalling.

Common causes

What causes a P0340 fault code?

P0340 can be caused by sensor, wiring, timing, oil-control and synchronisation issues.

Very common

Faulty camshaft position sensor

The sensor can fail internally and send a missing, weak or inaccurate signal.

Wiring

Damaged sensor wiring

Heat, oil, vibration or previous repair work can damage the cam sensor wiring loom.

Connector

Corroded or loose connector

Oil contamination or poor pin contact can interrupt the signal.

Electrical

Poor power or ground

The sensor needs a stable supply, ground and signal path to work correctly.

Timing

Timing chain stretch

If cam timing drifts too far, the cam and crank signals may not agree.

VVT system

Variable valve timing fault

Oil control or VVT actuator issues can affect cam position and trigger related faults.

Oil issue

Dirty or wrong engine oil

On VVT engines, poor oil condition can affect cam timing control and sensor readings.

Signal target

Damaged camshaft reluctor

A damaged trigger wheel or signal target can prevent a clean camshaft signal.

Rare

ECU signal fault

Rare, but possible after sensor, wiring and timing checks are complete.

Diagnosis

How a garage should diagnose P0340

✅ Scan all stored, pending and permanent codes.

✅ Record freeze frame data before clearing anything.

✅ Check whether P0340 appears alone or with crank/timing/VVT codes.

✅ Inspect the camshaft sensor connector and wiring.

✅ Check sensor power, ground and signal where applicable.

✅ Compare camshaft and crankshaft synchronisation data.

✅ Check live cam signal during cranking and running.

✅ Inspect oil level and oil condition on VVT engines.

✅ Check timing chain or belt condition if correlation looks wrong.

Avoid this mistake

Do not ignore timing clues

If the engine rattles on start-up, has poor service history, has VVT codes or shows cam/crank correlation faults, the problem may be deeper than a simple sensor.

Replacing the cam sensor may temporarily clear the light, but if the timing chain is stretched or oil control is poor, the fault can return.

Camshaft vs crankshaft signal

P0340 vs P0335 — what is the difference?

P0340 relates to the camshaft position sensor circuit. P0335 relates to the crankshaft position sensor circuit. The ECU uses both signals together to understand engine speed, crank position, cylinder phase and timing synchronisation.

P0340

Camshaft signal fault. Often linked to hard starting, VVT, timing or cam sensor wiring.

P0335

Crankshaft signal fault. More likely to cause sudden cutting out or crank-no-start.

Both together

Check cam/crank synchronisation, timing chain/belt condition and sensor signals carefully.

Read P0335 Guide Read P0011 Timing Guide
UK repair cost guide

How much does P0340 cost to fix in the UK?

Costs vary by vehicle, sensor access, wiring condition, engine layout and whether there is a timing or VVT issue behind the fault. These are rough UK guide prices only.

Diagnostic scan and live data check

Usually around £40–£120 depending on how much signal and timing data testing is included.

Camshaft sensor replacement

Often moderate if access is simple, but some sensors are awkward to reach.

Wiring or connector repair

Cost depends on where the fault is and how much loom access is needed.

Oil service / VVT checks

May be needed if dirty oil or oil control is affecting cam timing.

Timing chain or belt diagnosis

Can cost more if cam/crank correlation shows a mechanical timing issue.

Advanced oscilloscope testing

Useful for proving cam and crank signal quality before replacing expensive parts.

Safe driving advice

Can you drive with a P0340 code?

If the car starts normally, drives smoothly and the engine light is steady, short careful driving may be possible. However, P0340 should not be ignored because an unreliable camshaft signal can cause hard starting, limp mode, poor running or cutting out.

✅ Lower risk: steady engine light, normal starting, no rough running and no power loss.

⚠️ Medium risk: hard starting, hesitation, rough idle, poor acceleration or repeat warning light.

🚫 High risk: crank-no-start, stalling, cutting out, severe misfire, limp mode or timing rattle.

Real experience

What I would check first

On a real car with P0340, I would first check whether the car has any timing, VVT or crankshaft sensor codes stored alongside it. That changes the direction of the diagnosis.

If P0340 is on its own, I would inspect the cam sensor plug and wiring, then check live cam signal. If the engine has a chain rattle, slow start, or cam/crank correlation fault, I would not ignore the possibility of timing chain stretch.

MOT implications

Will P0340 fail an MOT?

P0340 can lead to an MOT failure if it causes an emissions-related engine warning light, rough running, misfire, smoke, stalling or poor emissions. If the vehicle struggles to start or runs badly, repair it before presenting it for test.

Emissions risk

Poor cam timing information can affect fuelling, combustion and emissions.

Warning light issue

An engine warning light linked to emissions should be investigated before MOT.

Running fault

Misfire, stalling, smoke or unstable idle should be repaired before testing.

Engine light MOT guide Common MOT failures
Back to main hub

Browse more OBD fault code guides

P0340 is one common camshaft position sensor and timing signal diagnostic trouble code. For more common codes, meanings, symptoms, repair costs and MOT implications, use the main Motor Vehicle Expert fault-code hub.

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Frequently asked questions

Frequently Asked Questions About P0340

Find answers to common questions about P0340 camshaft position sensor faults, timing synchronisation, repair costs and MOT implications.

What does P0340 mean?

P0340 means the engine computer has detected a fault in the camshaft position sensor circuit. The ECU uses the camshaft signal to identify valve timing, cylinder position and engine synchronisation.

Can I drive with a P0340 code?

You should be careful with P0340. If the car starts and drives normally, short careful driving may be possible. If it stalls, cuts out, struggles to start, misfires, loses power or enters limp mode, get it checked quickly.

Will P0340 fail an MOT?

P0340 can lead to an MOT failure if it causes an emissions-related engine warning light, rough running, misfire, smoke, stalling or poor emissions during the test.

What causes a P0340 code?

Common causes include a faulty camshaft position sensor, damaged wiring, corroded connector, poor sensor power or ground, timing chain stretch, cam/crank correlation issues, oil contamination or ECU signal faults.

How much does P0340 cost to fix in the UK?

A diagnostic check may cost around £40 to £120. Camshaft sensor replacement can be moderate if access is simple, while timing chain, wiring or correlation faults can cost more depending on the vehicle.

Is P0340 the same as P0335?

No. P0340 relates to the camshaft position sensor circuit, while P0335 relates to the crankshaft position sensor circuit. The ECU often compares both signals to confirm engine timing and synchronisation.

About this guide

Based on practical mechanic-style diagnostic experience

Motor Vehicle Expert publishes practical UK vehicle guidance based on real-world mechanical knowledge and hands-on diagnostic experience. This P0340 guide is written to help drivers understand camshaft position sensor and timing signal faults before replacing parts unnecessarily.

Fault codes should always be treated as a starting point for diagnosis. If your car has hard starting, cutting out, limp mode, timing rattle, severe misfire or a crank-no-start problem, get professional help before continuing to drive.