P0340 – Camshaft Position Sensor Circuit means the ECM/PCM has detected a fault in the electrical circuit of the camshaft position sensor. This sensor provides timing data used for injector sequencing, ignition timing, and variable valve timing. When the circuit fails, the engine may crank without starting, run rough, or stall unexpectedly. You may also notice poor fuel economy and reduced performance. This guide explains what P0340 means, the symptoms, causes, detailed diagnosis steps, and the most effective repair options.
What Does P0340 Mean?
P0340 is a generic OBD-II code triggered when the ECM detects an incorrect, missing, or erratic signal from the camshaft position sensor circuit. The sensor typically generates a waveform based on camshaft rotation. The ECM compares it with the crankshaft sensor signal to control ignition timing and fuel delivery.
A failure in the sensor, wiring, reluctor, or ECM input will prevent accurate timing control, leading to starting issues, misfires, or stalling. Because the camshaft sensor is crucial for engine synchronization, this code demands quick diagnosis.
Quick Reference
- OBD-II Family: P-Code (Powertrain)
- Scope: Generic
- System: Engine Timing / Ignition / Fuel Management
- Difficulty Level: Moderate
- Estimated Repair Cost: €60–€350
- Last Updated: 28 November 2025
Real-World Example / Field Notes
A sedan arrived on a tow truck after a no-start condition. Scanning revealed P0340 with no camshaft RPM reading during cranking. The camshaft position sensor was receiving power but had an internal open circuit. Replacing the sensor restored proper operation, and the engine started immediately.
Another case involved an SUV with intermittent stalling. The camshaft sensor wiring harness had rubbed against a bracket, exposing the signal wire. Vibration caused the ECM to lose the signal momentarily, triggering P0340. Repairing the wire and securing the harness resolved the issue permanently.
Symptoms of P0340 – Camshaft Position Sensor Circuit
- Hard starting or no start: ECM cannot sync timing.
- Rough idle: Misfires due to incorrect timing.
- Stalling: Especially when slowing down or idling.
- Loss of power: Reduced engine performance.
- Poor fuel economy: Timing correction defaults.
- Check engine light: P0340 stored, sometimes with crank sensor codes.
Common Causes of P0340
Most Common Causes
- Failed camshaft position sensor
- Damaged or corroded sensor connector
- Broken or shorted wiring harness
- Faulty reluctor wheel on camshaft
- Incorrect installation of aftermarket sensor
Less Common Causes
- Faulty crankshaft position sensor (affects correlation)
- ECM/PCM internal fault
- Weak battery or voltage drop during cranking
- Oil contamination on magnetic sensor tip
- Timing-chain/belt slack affecting signal accuracy
Diagnosis: Step-By-Step Guide
P0340 diagnosis focuses on verifying power, ground, signal integrity, and sensor correlation with the crankshaft sensor.
Tools You’ll Need
OBD-II scanner, multimeter, oscilloscope (ideal), wiring diagrams, back-probe leads, and basic hand tools.
- Check for additional codes: Crankshaft sensor codes or timing codes provide important clues.
- Inspect connector: Look for corrosion, bent pins, or loose fit.
- Check sensor power supply: Most sensors require 5V reference and ground.
- Verify ground integrity: Perform voltage-drop test.
- Back-probe signal wire: Look for switching voltage or waveform during cranking.
- Use oscilloscope: Confirm clean, stable camshaft signal (square-wave or sine-wave depending on design).
- Inspect reluctor wheel: Ensure no missing teeth or damage.
- Check for oil contamination: Oil leakage can disturb magnetic sensor accuracy.
- Test crankshaft sensor: A failing crank sensor can cause erroneous camshaft readings.
- Check mechanical timing: Excessive slack or timing misalignment affects sensor signals.
Pro Tip: If the engine cranks but shows **no RPM signal** and P0340 sets instantly, perform voltage checks first—wiring issues are more common than sensor failure.
Possible Fixes & Repair Costs
- Replace camshaft position sensor: €40–€120
- Repair wiring or connectors: €30–€100
- Clean sensor and reluctor wheel: €0–€30
- Replace crankshaft sensor (if correlated fault): €40–€120
- Correct timing-chain/belt alignment: €150–€350+
- Replace ECM/PCM (rare): €200–€450+
Can I Still Drive With P0340?
Driving with P0340 is risky. The engine may stall without warning, fail to start, or misfire severely. Incorrect timing can cause drivability problems and potentially damage the catalytic converter. If the vehicle starts at all, drive only short distances until repairs are made.
Related Codes
- P0399 – Ignition Coil “R” Primary/Secondary Circuit
- P0364 – Reserved
- P0363 – Misfire Detected Fueling Disabled
- P0362 – Ignition Coil “L” Primary/Secondary Circuit
- P0361 – Ignition Coil “K” Primary/Secondary Circuit
- P0360 – Ignition Coil “J” Primary/Secondary Circuit
- P0359 – Ignition Coil “I” Primary/Secondary Circuit
- P0358 – Ignition Coil “H” Primary/Secondary Circuit
- P0357 – Ignition Coil “G” Primary/Secondary Circuit
- P0356 – Ignition Coil “F” Primary/Secondary Circuit
Key Takeaways
- P0340 indicates an electrical or signal fault in the camshaft position sensor circuit.
- Most causes involve sensor failure, wiring issues, or poor signal quality.
- Quick diagnosis prevents stalling, no-start conditions, and misfires.
- Always check the crankshaft sensor and timing components for correlation issues.
FAQ
Does P0340 always mean the camshaft sensor is bad?
No. Wiring problems, poor grounds, or crankshaft sensor issues can all trigger this code.
Can a bad battery cause P0340?
Yes. Low cranking voltage can disrupt sensor signals and confuse the ECM.
Will the engine crank but not start?
Often yes. The ECM may not fuel or spark correctly without camshaft data.
Is an oscilloscope required?
Not required, but extremely helpful for spotting signal dropouts or waveform issues.
Should the cam and crank sensors be replaced together?
Only if correlation faults or age-related issues suggest both are unreliable. Otherwise, replace the failed component.