P0340 Camshaft Position Sensor A Circuit Malfunction (Bank 1)
The camshaft position signal has failed, so the computer can't tell which stroke each cylinder is on — expect long cranking and rough running.
Misfire & ignition
Where the crank sensor tells the ECU where the crankshaft is, the cam sensor tells it which stroke the engine is on, so injection and spark go to the right cylinder rather than the one 360 degrees out. P0340 means that signal is missing or implausible. Many engines will still start by guessing and correcting, which is why the usual symptom is extended cranking rather than a no-start.
Diagnose P0340 on your specific vehicle Add your year, make and model for ranked causes, repair videos and the exact parts you needCan I keep driving?
Driveable
Usually yes, with longer cranking and possibly reduced power. Don't rely on it for a long trip until it's fixed.
How serious
Moderate to high. Usually driveable, but hard starting gets worse over time and the same connector and harness problems that cause it can progress to a stall.
Symptoms you'll notice
- Long crank before the engine catches, especially when cold
- Rough running or misfire
- Hesitation or surging under acceleration
- Occasional stall at idle
- Reduced power as the ECU falls back to a default timing strategy
What causes P0340
Ordered by what to check first — how likely each cause is, weighed against what it costs to rule out. Working down the list in order is what stops you replacing an expensive part to fix a cheap problem.
Failed camshaft position sensor
The usual answer, and typically an accessible part on the front or top of the cylinder head. Failures often start intermittent and heat-related.
Wiring or connector fault
Oil leaking past a cam-sensor O-ring wicks into the connector and corrodes the pins. Check for oil in the plug before replacing the sensor — otherwise the new one fails the same way.
Timing chain stretch or a jumped belt
If the cam is no longer where the crank says it should be, the ECU sees an implausible cam signal. This normally sets P0016 as well, so seeing the two together points at mechanical timing rather than the sensor.
Faulty variable valve timing actuator
On engines with cam phasers, an actuator stuck away from its commanded position moves the cam signal outside the expected window.
Damaged reluctor or cam trigger wheel
Less common, but a damaged trigger wheel produces a signal that degrades with engine speed rather than failing outright.
How to diagnose it
- Check the connector for oil intrusion and corrosion — this is the cheap fix people skip.
- Verify supply voltage and ground at the sensor connector with the key on.
- Watch the cam and crank signals on live data or a scope while cranking to see which one drops out.
- If P0016 is also stored, check mechanical timing before buying sensors.
Parts you might need
Tools for the job
- Multimeter
- OBD-II scanner with live data
- Torque wrench
Related trouble codes
- P0335 — Crankshaft Position Sensor A Circuit Malfunction
- P0016 — Crankshaft Position — Camshaft Position Correlation (Bank 1, Sensor A)
- P0011 — Camshaft Position A — Timing Over-Advanced or System Performance (Bank 1)
- P0300 — Random/Multiple Cylinder Misfire Detected
Fitment matters. Causes and parts above are the common cases for P0340 across vehicles. The specific part numbers, procedures and torque specs vary by year, make, model and engine — always confirm against service data for your vehicle before buying parts or starting work.