P0340

What P0340 means

This code means the engine computer isn't getting a proper signal from the camshaft position sensor. That sensor tells the computer where the camshaft is in its rotation, which is how the engine figures out when to fire each cylinder and when to open each injector. When the signal drops out, gets noisy, or never shows up at all, the computer sets this code. It's not necessarily telling you the sensor itself is bad — it's telling you the signal wasn't there or wasn't clean. Those are different problems.

Is it safe to drive

This one deserves early attention. Some engines will run rough, stall, or refuse to restart once warm. Others will keep running fairly normally on the crankshaft position signal alone, at least for a while. The risk is that if the computer loses track of cam timing, it can end up with a running condition that isn't matched right — fuel going in when it shouldn't, at the wrong time — and on some engines that can lead to real damage over miles driven, not just a rough idle. If the check engine light is flashing, or the car is stalling, hesitating, or hard to restart, don't keep driving it. If it's just the light on with no symptoms, it's worth getting looked at soon rather than putting it off for weeks.

What usually causes it

Most common first:

• Wiring problems — a chafed wire, corroded connector, or a plug that's worked loose near the sensor. This is very common and gets missed if someone jumps straight to replacing the sensor.
• The camshaft position sensor itself, worn out or failed.
• Oil contamination on the sensor tip, often from a small oil leak nearby, which fouls the signal.
• A stretched or slipped timing chain or timing belt, which throws off the actual physical timing the sensor is reading.
• On some engines, a failing engine control computer, though this is rare and should be the last thing suspected, not the first.

Which of these is likely depends a lot on the specific engine. Some engines are known for sensor wiring that runs close to a heat source and cracks over time. Others are known for timing chain wear at higher mileage. There's no single answer that fits every car.

Diagnosis and rough cost

Proper diagnosis means checking the wiring and connector first, then testing the sensor's actual signal with a scan tool or oscilloscope while the engine runs, rather than just reading the code and swapping the part. If the timing chain or belt is suspected, that's a bigger job to confirm and a bigger job to fix.

Cost varies a lot depending on what's actually wrong. A wiring repair or a straightforward sensor replacement is usually a modest job, often in the range of a couple hundred dollars including diagnosis and labor, depending on the engine and how accessible the sensor is. If it turns out to be a timing chain issue, that's a much larger repair, often running well into four figures. We won't know which of those it is until we've actually tested it, and we'd rather tell you that than guess.