P0340: Camshaft Position Sensor "A" Circuit (Bank 1 or Single Sensor)
Title: SAE J2012 generic definition. Manufacturer-specific definitions and enhanced codes can differ; check service information for the exact vehicle.
What P0340 means
The ECM isn't seeing a usable signal from the bank 1 (or only) camshaft position sensor.
What sets it
The cam sensor tells the ECM which stroke each cylinder is on, for sequential injection and, on many engines, coil-on-plug spark timing and variable valve timing. If the signal is missing or electrically wrong while the engine turns, P0340 sets. Many engines will still start using the crank signal alone, but often with a longer crank time.
Symptoms
- Long crank before starting
- Stalling or no-start on some engines
- Rough running or reduced power
- VVT-related codes alongside it
Is it safe to drive?
General guidance, not a guarantee: Often drivable, but if the engine stalls or won't restart, it isn't worth the risk. Diagnose before relying on the vehicle. If in doubt, have it towed and diagnosed.
Common causes
Listed roughly from most to least common in general practice. The real order varies by vehicle, mileage and history.
- Failed cam sensor
- Wiring or connector damage, including oil wicking into the connector
- Sensor supply circuit problem shared with other sensors: a shorted sensor on the same reference circuit can pull it down
- Timing belt or chain problem: jumped timing can upset the signal
- Damaged tone wheel or reluctor
Test before you replace: diagnostic sequence
General guidance only. Always follow the vehicle manufacturer's service information, specifications and safety procedures. Any figures below are general guidelines that defer to the manufacturer's specification.
- Note whether other sensor codes set at the same time. Several sensor codes together suggest a shared reference or ground fault.
- Inspect the sensor connector for oil, corrosion or a backed-out terminal.
- With the key on, check the sensor's reference voltage and ground at the connector per the wiring diagram; voltage-drop test the ground under load.
- Scope the cam signal while cranking or running, ideally together with the crank signal, and compare with a known-good pattern.
- If the signal is present but its relationship to crank is wrong, check mechanical timing (see P0016).
- Replace the sensor only when supply and ground are good and the signal is missing or distorted.
Bench note: Oil inside the connector is a common find on some engines. Fix the leak path or the new sensor will fail again.
How-to guides for this code
Related codes
FAQ
Will the engine run without a cam sensor?
Many engines can run on the crank signal alone, with a longer crank time and reduced performance. Others won't start. It depends on the engine strategy.
P0340 after a timing belt job: why?
The timing may be off by a tooth, or the sensor connector or tone wheel may have been disturbed. Check the timing marks before replacing the sensor.
Cam sensor or crank sensor: which is which?
P0340 is cam ("A", bank 1 or single sensor). P0335 is crank.
Sources
- SAE J2012, Diagnostic Trouble Code Definitions (standard page; code titles only)
- Generic code title cross-check: obd-codes.com generic code list
Written with AI assistance and reviewed for accuracy; not a substitute for OEM service information. Shop Docs Studio is not affiliated with SAE, EPA, CARB or any vehicle manufacturer.