P0340 Code: Camshaft Position Sensor 'A' Circuit Malfunction (Bank 1)
The engine computer is not receiving a usable signal from the bank-1 camshaft position sensor, which tells it where the camshaft is so fuel injection and ignition can be timed correctly.
What this means for driving
A failed camshaft sensor can make the engine hard to start, stall, or run roughly — and stalling in traffic is itself a safety concern. If the engine stalls, will not restart reliably, or runs very roughly, have it assessed promptly and avoid driving it until the cause is known.
When in doubt, have a mechanic assess it promptly. If any of the red-flag symptoms below are present, stop driving and arrange a tow rather than risking it.
Important: This page is general information only — not professional mechanical advice and not a diagnosis for your specific vehicle. Fault causes and severity vary by make, model, year, and condition. A qualified mechanic should confirm any diagnosis before you make driving decisions or authorize repairs.
Red-flag symptoms: stop and get help
- Engine stalls repeatedly or will not restart
- Engine will not start at all
- Severe bucking or loss of power while driving
Symptoms of P0340
- Hard starting or no start
- Engine stalling
- Rough running
- Loss of power
- Check-engine light on
- Poor fuel economy
Most likely causes, ranked
- Faulty camshaft position sensor — the most common cause
- Damaged wiring or corroded connector to the sensor
- Timing chain or belt problem affecting camshaft timing
- Faulty engine computer (rare)
How a mechanic diagnoses it
- Sensor signal checked with a scan tool and oscilloscope while cranking.
- Wiring and connector inspected for damage or corrosion.
- Timing checked if the sensor and wiring test good.
Likely fixes
- Replace camshaft position sensor
- Repair wiring or connector
- Timing chain/belt service (if timing is the cause) (Shop job)
Repair costs vary by vehicle, region and shop. Get a quote from a local mechanic.
Related codes
- P0335: Crankshaft Position Sensor 'A' Circuit Malfunction
- P0300: Random/Multiple Cylinder Misfire Detected
CheckMyCarCode content is general information only and is not a substitute for professional diagnosis. Trouble-code meanings are standardized for generic (P0xxx) codes, but causes, severity, and repairs vary by vehicle. If your car shows a red-flag symptom, stop driving and get professional help.