OBD Code P0340: Camshaft Position Sensor Circuit — Hard Starting or No Start

What does code P0340 mean?

Code P0340 (Camshaft Position Sensor Circuit Malfunction — Bank 1) means the ECU isn't receiving a valid signal from the camshaft position sensor (CMP). This sensor tells the ECU the position of the camshaft (valve timing), which is used to synchronise sequential fuel injection.

Without it, the ECU falls back to less precise injection timing — hard starting results.

Symptoms

• Check engine light
• Hard starts — engine cranks for a long time before firing, especially cold
• Occasional stalling
• Slight loss of power
• Often accompanied by P0335 — if both appear, check the timing chain/belt first

Causes

1. Failed CMP sensor (60%)

Sensors fail with age, heat, and vibration. Inexpensive to replace.

👉 Camshaft position sensor on Amazon UK — £15-50

DIY replacement (20-40 min):

1. Find the sensor at the top of the engine (near cylinder head)
2. Unplug connector
3. Remove fixing bolt (M6)
4. Gently twist out the sensor
5. Install the new sensor clean and dry (no oil on the tip)
6. Clear the code

2. Damaged trigger wheel on camshaft

Small ferrous target wheels can corrode or chip.

3. Wiring fault

Inspect the harness for chafing against moving components.

P0340 + P0016: timing issue?

If P0016 (crankshaft/camshaft correlation) accompanies P0340, do not drive — this combination can indicate a jumped timing chain/belt.

Repair cost