P0340: OBD-II code P0340 flags a fault in the camshaft position sensor circuit — the PCM cannot see cam position, which affects ignition and injection timing.

Symptoms

• The check engine light is on and the engine may crank but be slow to start, or in severe cases fail to start at all.
• Rough running, hesitation, stalling, and reduced power because the PCM has to default to a limp fuel and spark strategy.
• Sudden stalling while driving, followed by extended cranking to restart — a classic failing-cam-sensor symptom.

Common causes

• A failed camshaft position sensor — the most common cause, with the sensor's internal Hall-effect chip degrading with heat over time.
• Damaged wiring or a corroded connector at the cam sensor, common near the timing cover on high-mileage engines.
• A stretched or skipped timing chain, or a damaged reluctor wheel/tone ring on the camshaft producing missing pulses.

What to do?

Read live camshaft position data and compare to crankshaft position — the two should stay locked in phase. Inspect the cam sensor's connector for oil intrusion or corrosion. Replace the sensor if it reads erratically or has no signal. If replacement doesn't fix it, inspect timing chain stretch and the reluctor wheel for damage.