P0343 Code: Camshaft Position Sensor A – Circuit High Input

Camshaft Positon Sensor

What does the P0343 code mean?

The P0343 is triggered when the engine control unit receives a faulty signal or a high circuit input from the camshaft position sensor. Common causes are a bad camshaft position sensor or bad wiring. The camshaft position sensor is mounted on one of your camshafts. The P0343 is a general error code that applies to all makes and models from about the year 2000 onwards.

Some engines have several camshaft position sensors. Since the camshaft must be synchronized with the crankshaft position sensor at the starting torque, a common symptom is that your engine is difficult or impossible to start.

The 4-stroke crankshaft rotates two revolutions in one cycle and the camshafts rotate one revolution per cycle. Older cars usually have no camshaft sensor and only one crankshaft sensor. This is because older cars do not need to know which of the revolutions the crankshaft rotates at.

P0343

Each cylinder ignites the ignition and fuel once every two crankshaft revolutions, and it uses the camshaft sensor to detect whether the cylinder is in the intake or combustion cycle. Older cars without a camshaft sensor ignite the spark plugs twice per revolution, which is why it is called a “wasted spark”. So instead of igniting the ignition coils twice per revolution, when this is only required once per revolution, a camshaft sensor is used.

CodeDescriptionCommon CausesPossible Solutions
P0343Camshaft Position Sensor A - Circuit High InputFaulty Camshaft position sensor

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)
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

Replace Camshaft position sensor

Replace Engine control unit(ECM/PCM) (Rare)

P0343 Symptoms

The most common symptom of the P0343 code is the check engine light coming on, and the engine may have long starting times or it may not start at all. Sometimes, no symptoms at all can be expected for fault 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 code P0343 is a faulty camshaft position sensor or faulty wires to the camshaft position sensor. A common misdiagnosis of this error code is that it could be a faulty timing belt drive causing the P0343 code. This error code indicates that there is a faulty circuit to the camshaft position sensor and should not be confused with the other error codes of the camshaft position sensor.

Possible Solutions

  • Charge your car battery, replace the 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 cleanerIr?T=Askamastermec 20&Amp;L=Am2&Amp;O=1&Amp;A=B00006Lveu.
  • 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 problem. It may require some knowledge of car electronics and the necessary tools, but you may get good information on how to do it right and how to do it without replacing non-defective parts. Always connect a car battery charger when doing any work on your car, because low voltage can trigger other error 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 or bad connections.
  4. Measure the ohms between the pins toward the camshaft sensor with a digital multimeterIr?T=Askamastermec 20&Amp;L=Am2&Amp;O=1&Amp;A=B018Exzo8M. 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 oscilloscopeIr?T=Askamastermec 20&Amp;L=Am2&Amp;O=1&Amp;A=B012938E76 (advanced).
  7. Replace camshaft sensor if faulty, and repair any wirings.
  8. Erase the code and take 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 may still be stored without the check engine light being on.

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

Recommended Tools to Fix P0343

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Written by: Magnus Sellén

Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.