Camshaft Position Sensor A Circuit Bank 1
The Powertrain Control Module (PCM) detected a malfunction or loss of signal in the Bank 1 camshaft position sensor 'A' circuit. This means the engine computer cannot accurately determine the position of the camshaft relative to the crankshaft, which is necessary for proper fuel injection and ignition timing.
This code is considered high severity because a failing camshaft position sensor can cause the engine to stall unexpectedly or fail to start, potentially leaving you stranded. It should be diagnosed and repaired as soon as possible.
Common symptoms
- Illuminated Check Engine Light
- Hard starting or extended cranking time
- Engine stalling or hesitation while driving
- Rough idling or engine misfires
- Noticeable decrease in engine power and fuel economy
Likely causes
- Faulty camshaft position sensor (Bank 1)
- Damaged, corroded, or loose wiring and connectors in the sensor circuit
- Weak or dead car battery causing low system voltage
- Faulty crankshaft position sensor (often sets concurrent codes)
- Damaged reluctor ring or timing components
- Failed Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Check the battery voltage and charging system.
Look for: A weak battery or failing alternator can cause low voltage to the sensor, triggering the code. Ensure resting voltage is around 12.6V and charging voltage is 13.5V-14.5V.
Visually inspect the camshaft position sensor wiring and connector.
Look for: Look for frayed wires, melted insulation, or a loose/corroded connector. Any physical damage or poor connection can interrupt the sensor signal.
Test the sensor's power and ground circuits using a digital multimeter.
Look for: With the key on, engine off, verify the sensor is receiving the correct reference voltage (usually 5V or 12V depending on the vehicle) and has a solid ground. Missing voltage or ground indicates a wiring or PCM issue.
Check the sensor signal output using an oscilloscope or advanced scan tool.
Look for: Observe the signal waveform while cranking or running the engine. A missing, erratic, or distorted square wave (for Hall effect) or AC sine wave (for VR sensors) indicates a faulty sensor or damaged reluctor ring.
Inspect the camshaft reluctor ring and timing components.
Look for: Remove the sensor and inspect the tone ring for missing teeth, damage, or excessive debris. Also, check for excessive timing chain/belt slack that could throw off the cam/crank correlation.
This page explains the generic P0340 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.