The ECU has lost or seen an out-of-range signal from the camshaft position sensor.
P0340 — also written PO34O, P 0340, 0340 — is the OBD-II code for camshaft position sensor 'a' circuit malfunction. Same code, same fix: this page covers every spelling of it.
This is your engine losing its 'eyes' for the top end, usually down to a failed pick-up sensor or a timing chain that's stretched like an old jumper. It's a common plague on Vauxhall Corsas and Nissans that haven't had their oil changed enough.
P0340 is a sensors fault code, typically costing £60–£350 to put right in a UK garage.
What P0340 actually feels like to drive
- The car cranks for ages before finally firing up (limp mode start).
- Engine suddenly cuts out while waiting at a roundabout or junction.
- A noticeable lack of 'grunt' or pick-up, feeling like the turbo isn't boosting.
- The rev counter bounces erratically or drops to zero while driving.
- The car smells of unburnt petrol because the ECU is guessing the fuel timing.
What causes P0340?
- Failed cam sensor
- Damaged wiring or connector
- Loose sensor mounting
- Timing chain wear changing the air gap
UK vehicles that throw P0340 most often
- Vauxhall Corsa D/E 1.2 & 1.4 (A12XER/A14XER) 2009-2017
- Nissan Qashqai 1.5 dCi (K9K) 2007-2013 (Wiring loom issues)
- Ford Focus Mk2/Mk3 1.6 TDCi 2008-2015
- BMW 1 Series (N43/N47 engines) 2007-2013
- Vauxhall Insignia 2.0 CDTi (A20DTH) 2008-2015
- Toyota Yaris 1.0 & 1.3VVT-i 2005-2011 (Sensor failure)
How P0340 is fixed
- Replace cam sensor (cheap, common fix)
- Repair wiring loom or connector
- On chain-driven engines, check chain wear before condemning sensor
The P0340 misdiagnosis that wastes money
I see it every week: folks chuck a cheap £15 sensor from an auction site at the car and get nowhere. The biggest blunder with a P0340, especially on the Vauxhall 1.2 and 1.4 Ecotec engines, is ignoring the timing chain. If that chain has stretched just a few millimetres, the cam and crank signals fall out of sync. You can fit twenty Bosch sensors and it won't fix the car because the physical timing is "soft." Always check the live data for "cam/crank sync status" before assuming it's an electrical fault.
What a UK garage should charge for P0340
At an indie like mine, you're looking at £40–£60 for a diagnostic plug-in. A genuine Bosch or Denso sensor usually runs between £40 and £90 plus half an hour of labour (£40). If it’s just the sensor, you're out the door for £150. However, if that chain is stretched on a Corsa, you’re looking at a £500+ job for a full kit and labor. Main dealers will easily double these prices, charging £150 just to look at the dashboard.
P0340 repair cost in the UK
Most P0340 repairs land between £60–£350 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P0340
If a garage tells you the sensor is dead, ask them: "Did you check the scope pattern or just read the code?" A proper tech will use an oscilloscope to see if the signal is 'square.' If you’re driving an Insignia or an Astra, insist they inspect the wiring loom near the top of the head—vibration often rubs the insulation raw, causing a short that looks like a dead sensor. Don't let them 'parts-cannon' it; make sure they've checked the air gap and the reluctor ring for iron filings first.
Can you drive with P0340?
Drivable, but expect crank-no-start or stalling at random — may also cause non-start hot.
Urgency: medium.