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P0343 Code: Camshaft Position Sensor A – Circuit High Input


What does the P0343 code mean?



The P0343 is a generic trouble code which applies to all makes and models from around the year 2000. The code is telling us that the engine control unit is getting a fault in the circuit to the camshaft position sensor. The camshaft position sensor is fitted at one on one of your camshaft.


Some engines do have several camshaft position sensors. Because the camshaft needs to have synchronization with the crankshaft sensor in the startup moment, a common symptom is that your engine will be hard to start or not start at all.

The 4-stroke crankshaft rotates two turns on one cycle and the camshafts are rotating one turn per cycle. Older cars do usually not have a camshaft sensor and only a crankshaft sensor. This is because older cars do not have to know at which of the turns the crankshaft is at.

Each cylinder is firing the ignition and fuel once per each two crankshaft turns and it uses the camshaft sensor to recognize if the cylinder is at the intake or combustion cycle. Older cars without a camshaft sensor are firing the spark plugs two times per turn and therefore, it’s called “Wasted spark”. So instead of firing the ignition coils two times per turn, when it’s only required to do it once per turn, it uses a camshaft sensor.

The p0343 is being triggered when the engine control unit is getting a faulty signal/high circuit input from the camshaft position sensor.


P0343 Symptoms

The most common symptom of the P0343 code is the Engine Light ON and the engine can have long cranking times or it will not start at all. Sometimes you do not expect any symptoms at all for the trouble code P0343.

  • Check engine light/Service engine soon light ON
  • The engine may not start
  • Engine dies when driving
  • Hard starting conditions/Long cranking time
  • Rough Idle
  • Rough Acceleration
  • Hard shifting
  • No symptoms


Possible Causes

The most common cause of the P0343 code is a faulty camshaft position sensor or faulty wires to the camshaft position sensor. A common misdiagnosing of this trouble code is that it could be a faulty timing belt timing that will cause the p0343 code. This trouble code is telling us that there is a faulty circuit to the camshaft position sensor and should not be mistaken for the other camshaft position sensor trouble codes.

  • Faulty Camshaft position sensor (Most common)
  • Faulty 5v power supply wire from ECM
  • Corrosion/Bad connection in the CPS connector
  • Faulty ground wire to ECM
  • Short between power and ground wire
  • Low battery voltage / Faulty alternator
  • Faulty starter
  • Faulty Engine control unit (ECM)


Possible Solutions

  • Charge your car battery/Replace battery or fix the alternator charging problems
  • Repair any faulty wires between the camshaft position sensor and the engine control unit
  • Clean the camshaft position sensor from oil.
  • Clean the Camshaft position sensor connector with a Spray contact cleanerP0343 Code: Camshaft Position Sensor A - Circuit High Input.
  • Replace Camshaft position sensor
  • Replace Engine control unit(ECM/PCM) (Rare)


How to diagnose the P0343 code

This is a guide to how an automotive technician would diagnose this issue. It may require some car electrical skills and the required tools, but you may get some good information about how to do it the right way, without replacing any parts that are not faulty. Always connect a car battery charger when you are doing any work with your car, because low voltage can trigger other trouble codes and even damage control units.

  1. Measure the voltage at idle (>14 volts) and with the engine off ( >12 volts )
  2. Connect an OBD2 code scanner to verify the P0343 code
  3. Inspect the camshaft position sensor for any external damages and make sure it is not fouled by oil from an oil leak. Inspect the connector and check for any corrosion/bad connection.
  4. Measure the ohms between the pins toward the camshaft sensor with a Digital MultimeterP0343 Code: Camshaft Position Sensor A - Circuit High Input. If you get no connection between the pins, there might be an open circuit inside the camshaft position sensor
  5. Remove the connector from the engine control unit and find the pins to the camshaft position. Do the same procedure with the camshaft position sensor connector plugged in. If you get no connection between these pins there might be an open circuit in the wirings. Check for any connection between the wires. If there is a connection between the wires, the wires are shorted.
  6. Check the signal from the crankshaft sensor with an oscilloscopeP0343 Code: Camshaft Position Sensor A - Circuit High Input ( Advanced ).
  7. Replace camshaft sensor if faulty/Repair wirings
  8. Erase the code and make a test drive to verify that the problem is gone. Check your trouble code memory after some test drives to be sure that the problem is gone. The code can still be stored without the engine light to be ON.

If you do not find any damages to the wires or camshaft position sensor, it may be a faulty engine control unit. But these cases are really rare and you should do a correct troubleshooting before replacing your engine control unit, as they are quite expensive.


Recommended Tools to Fix P0343


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