How to Fix P0340: Camshaft Sensor Replacement Cost

Your car turns over fine but won't fire, or it starts rough and stalls at the first red light. The check engine light is on, and the scan returns P0340: the ECU isn't getting a valid signal from the Bank 1 camshaft position sensor. On most cars that's a straightforward fix. On some it's the reason the engine won't start at all.

What are the symptoms of P0340?

How P0340 shows up depends on whether the camshaft signal drops out completely or only becomes intermittent. The common patterns:

• Engine cranks but won't start, or takes much longer than usual to fire, when the ECU needs the cam signal to time injection.
• Rough idle and stalling, often worse once the engine is warm and the sensor heats up.
• Hesitation or power loss under acceleration, as the ECU falls back to a safe ignition map.
• Intermittent stalling that clears on a restart, the classic signature of a sensor failing as it warms.
• Check engine light, sometimes with the engine in a reduced-power limp mode.

A sensor that has failed outright tends to cause a hard no-start, while one on its way out throws intermittent stalls and warm-restart problems first. Either way the code points at the same circuit; the next step is finding out whether the sensor, the wiring, or the timing chain is behind it.

What causes P0340?

Failed CMP sensor. The most common cause. These sensors are either Hall effect or magnetic reluctor types, and they fail from heat, vibration, and general age. Most last 100,000-200,000 km. When the internal element fails, the signal drops out completely or becomes intermittent. Damaged wiring or connector. The sensor connector and wiring are exposed to engine heat and vibration. Corroded pins cause weak signals. Chafed wires or a loose connector push it over into complete signal loss. Timing chain stretch or jump. If the timing chain has stretched or skipped a tooth, the camshaft position relative to the crankshaft changes beyond expected parameters. This can trigger both P0340 and P0016. Damaged reluctor wheel/tone ring. The sensor reads a toothed wheel on the camshaft. If a tooth is damaged or the wheel has shifted, the signal pattern becomes invalid. Low battery voltage. A weak battery can cause insufficient signal voltage from the CMP sensor during cranking, triggering P0340 intermittently.

How do you diagnose P0340?

Step 1: Check for related codes. P0340 with P0016 suggests timing chain issue. P0340 alone usually means sensor or wiring. Step 2: Inspect the sensor connector for corrosion, damage, or looseness. Unplug, inspect, clean, and reconnect firmly. Step 3: Test sensor resistance and signal output with a multimeter or oscilloscope. Compare to manufacturer specifications. Step 4: If the sensor and wiring test good, check timing chain condition, especially if the engine has high mileage or you hear cold-start rattle.

Stuck on the driveway with P0340 and not sure if it is safe to limp to a shop, Skanyx reads the code with freeze frame data, gives you a green-to-red safe-to-drive verdict, and tracks engine RPM, calculated load, and the stored-vs-pending pattern across repeat scans, so in about a minute you know whether the sensor is dying intermittently or fully dead and what to do next. For more on reading these live data streams, the raw sensor signal trace is a manufacturer-extended PID and needs a brand-specific tool when you want to verify before vs after replacement. skanyx.com/download

What does it cost to fix P0340?

Prices estimated as of March 2026.

Start at the connector: clean, reseat, and rescan before ordering any parts. If P0340 persists and no timing chain codes are stored alongside it, a replacement CMP sensor is almost always the end of the job. P0340 paired with P0016 is a different situation: get the timing chain inspected before putting money into sensors. For a broader look at engine faults that can accompany a failing cam sensor, see the rough idle causes guide and the check engine light overview.