Faulty camshaft position sensor (35% likelihood): The CMP sensor has failed in a mode that produces higher-than-expected voltage output, either from internal degradation or a stuck-high failure mode. Wiring short to voltage (30% likelihood): A short circuit in the CMP sensor wiring harness is introducing external voltage into the signal circuit, producing artificially high readings at the ECM. Corroded or damaged connector (20% likelihood): Corrosion or physical damage to the CMP sensor connector pins is creating abnormal electrical resistance that elevates the signal voltage. Incorrect sensor installed (10% likelihood): An aftermarket or incorrect CMP sensor with different electrical characteristics was installed, producing output voltage outside the ECM's expected range. ECM fault (5% likelihood): An internal ECM circuit fault is causing it to incorrectly interpret the CMP sensor signal as higher than actual.

How much does it cost to fix P0343?

DIY repair typically costs $15–$80 for parts. Professional repair runs $100–$350 including parts and labor.

P0343

Powertrain

Moderate

Camshaft Position Sensor A Circuit High Input (Bank 1 or Single Sensor)

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The P0343 code means the camshaft position sensor on Bank 1 is sending a voltage signal that exceeds the maximum expected threshold. This is the opposite of P0342 (low input) and often points to a wiring issue rather than a simple sensor failure, since a short to battery voltage in the signal wire can push the reading above the ECM's acceptable range.

The camshaft position sensor is essential for proper engine timing and fuel injection control. When the ECM receives an abnormally high signal, it may enter a failsafe mode that affects engine performance, starting ability, and fuel economy. In some vehicles, a persistent high signal can prevent the engine from starting altogether.

Diagnosis should start with a careful inspection of the wiring harness. Look for any spots where the signal wire may be chafed against a metal bracket or another wire, which could create a short to voltage. Also check that the correct sensor is installed — aftermarket sensors sometimes have different output characteristics. If the wiring checks out, replacing the sensor usually resolves the issue. This is typically an easy and affordable repair that most DIYers can handle.

Severity

Moderate — Address SoonThis Week

Symptoms

•Engine is hard to start or cranks excessively
•Check Engine light is on
•Engine runs rough or misfires
•Stalling at idle or low speeds
•Noticeable loss of engine power
•Poor fuel economy

Likely Causes

Faulty camshaft position sensor35%

The CMP sensor has failed in a mode that produces higher-than-expected voltage output, either from internal degradation or a stuck-high failure mode.

Wiring short to voltage30%

A short circuit in the CMP sensor wiring harness is introducing external voltage into the signal circuit, producing artificially high readings at the ECM.

Corroded or damaged connector20%

Corrosion or physical damage to the CMP sensor connector pins is creating abnormal electrical resistance that elevates the signal voltage.

Incorrect sensor installed10%

An aftermarket or incorrect CMP sensor with different electrical characteristics was installed, producing output voltage outside the ECM's expected range.

ECM fault5%

An internal ECM circuit fault is causing it to incorrectly interpret the CMP sensor signal as higher than actual.