Camshaft Position Sensor A Circuit High (Bank 1 or Single Sensor)
The P0343 code indicates that the Engine Control Module (ECM) has detected an abnormally high voltage signal from the Bank 1 Camshaft Position Sensor 'A' circuit. This usually means the sensor's signal voltage is stuck high or exceeding the maximum expected threshold for a specific amount of time.
A failing camshaft position sensor can cause the engine to stall unexpectedly or fail to start, leaving you stranded. It should be diagnosed and repaired immediately to ensure reliable vehicle operation.
Common symptoms
- Illuminated Check Engine Light
- Hard starting or extended cranking time
- Engine stalling or hesitation while driving
- Rough idle and poor engine performance
- Reduced fuel economy
Likely causes
- Defective camshaft position sensor
- Short to voltage in the sensor wiring harness
- Poor electrical connection or corrosion at the sensor connector
- Damaged or misaligned reluctor ring/tone wheel
- Faulty Engine Control Module (ECM)
What to check before replacing parts
Visually inspect the camshaft position sensor wiring and connector
Look for: Look for frayed wires, melted insulation, corrosion, or pushed-out pins that could cause a short to voltage or poor connection.
Monitor the sensor data using an OBD-II scan tool
Look for: Observe the camshaft position sensor PID while cranking or running; look for a signal that is stuck high (e.g., constant 5V or 12V) instead of toggling.
Check the sensor power and ground circuits
Look for: Use a multimeter to verify the sensor is receiving the correct reference voltage (usually 5V or 12V depending on the system) and has a solid ground with minimal resistance.
Test the sensor signal wire for a short to voltage
Look for: Disconnect the sensor and the ECM, then measure voltage on the signal wire with the key on; any voltage present indicates a short to power in the wiring harness.
Analyze the sensor output signal with an oscilloscope
Look for: Back-probe the signal wire while the engine is cranking or running; look for a clean square wave pattern that drops to near 0V and rises to the reference voltage without staying stuck high.
This page explains the generic P0343 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.