P0340: Camshaft Position Sensor "A" Circuit (Bank 1 or Single Sensor)

What does P0340 mean?

The camshaft position (CMP) sensor tells the ECM where the camshaft is, so it can time fuel injection and, on many engines, spark and variable valve timing. Together with the crankshaft sensor, it lets the ECM know exactly which stroke each cylinder is on.

P0340 is a circuit code. It means the ECM has detected a missing, intermittent or implausible signal from sensor A, which is the bank 1 or only camshaft sensor. It does not always mean the sensor itself has failed.

Related codes, such as P0341 for range or performance, or crankshaft sensor codes like P0335, help narrow down the cause.

Common symptoms

• Check engine light on
• Long cranking or a no start condition
• Stalling, especially when hot or at idle
• Rough running or misfires
• Reduced power or limp mode on some vehicles

Common causes

The causes below are the ones commonly seen with P0340. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• A faulty camshaft position sensor
• Damaged wiring, a loose connector or corroded pins
• Low battery voltage or a weak charging system affecting the signal
• A damaged reluctor ring or tone wheel on the camshaft
• Timing chain or belt problems that change cam to crank alignment
• A failing ECM (rare)

What to check with a scanner

• Check the battery and charging voltage first. In Live data, look at control module voltage with the engine running.
• Inspect the sensor connector and wiring for damage, oil contamination or loose pins.
• Check freeze frame data to see if the code set during cranking, at idle or while driving.
• Note any other timing related codes, such as P0335 or cam and crank correlation codes, which change the diagnosis.

How to read and clear P0340 with OBD Master Pro

1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0340 is listed and note any other codes, since they often explain the cause.
5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0340 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0340.

When to see a mechanic

Get professional help if any of these apply:

• The car will not start or stalls while driving
• The code returns after replacing the sensor
• You hear rattling from the timing chain area
• Several timing or correlation codes are stored together

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

Related trouble codes

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