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DTC codes / P03xx · Ignition system and misfire / P0343

P0343Camshaft Position Sensor A Circuit High Input

P0343 means the engine computer has detected an abnormally high voltage on the signal circuit from camshaft position sensor A, which is the sensor that tells the computer the exact position of the camshaft for fuel and ignition timing. The computer expects the sensor signal to switch between a low and high voltage as the camshaft rotates, and a continuous high reading indicates a short to voltage, an open ground, or a failed sensor.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Engine may crank but fail to start or start after a long crank
  • Rough idle, misfire, or stalling, especially when the engine is cold
  • Reduced engine power or limp mode with the throttle response limited
  • Poor fuel economy or increased emissions due to incorrect timing
  • In some vehicles, a no-start condition because the computer cannot determine camshaft position

Common causes, most likely first

  1. Faulty camshaft position sensor A
  2. Damaged or shorted signal wire between the sensor and the engine computer
  3. Corroded, loose, or disconnected sensor connector
  4. Open or high-resistance ground circuit at the sensor
  5. Failed engine computer driver circuit for the sensor
  6. Metal debris or a damaged reluctor wheel on the camshaft affecting the signal
  7. Aftermarket electrical accessories improperly wired into the sensor circuit

How to diagnose and fix it

  1. Inspect the sensor connector and wiring for corrosion, chafing, or loose pins, and repair as needed
  2. Measure the sensor reference voltage and ground at the connector with a digital multimeter to confirm the circuit integrity
  3. Check the signal wire for a short to voltage or an open circuit by back-probing the computer connector
  4. Compare the camshaft sensor signal with a known-good waveform using an oscilloscope if available
  5. Replace the camshaft position sensor if the circuit tests good but the signal remains stuck high
  6. Clear the code and perform a road test to verify the repair, including a cold start and a steady cruise
  7. If the code returns, check the engine computer and its connectors for water intrusion or internal faults

What a high cam signal really tells you

  • A P0343 is often set by a simple unplugged or loose connector after recent engine work, so always check the sensor plug before condemning the sensor.
  • The code can be triggered by a short to voltage on the signal wire from a nearby damaged harness, especially where the wiring rubs against the engine cover or accessory belt.
  • Some vehicles use a three-wire hall-effect sensor and others use a two-wire variable reluctance sensor; the diagnostic steps differ, so confirm the sensor type before testing.
  • A failing camshaft sensor may still produce a signal when cold but drop out when hot, so an intermittent no-start with a P0343 often points to a thermally failing sensor rather than a wiring fault.
  • Replacing the sensor without checking the ground circuit is a common misdiagnosis, because a high-resistance ground will cause the same high-voltage reading at the computer.

Can I keep driving with P0343?

You can usually drive the vehicle to a repair shop if the engine starts and runs without severe misfiring, but avoid heavy acceleration and long trips because incorrect camshaft timing can cause poor fuel economy and increased emissions. If the engine stalls, misfires badly, or fails to restart, stop driving and have the vehicle towed to prevent catalytic converter damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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