P0340 – Camshaft position (CMP) sensor A, bank 1 circuit malfunction

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By Benjamin Jerew (Contact Me)
Last Updated 2022-11-22
ASE Master Tech
CodeFault LocationProbable Cause
P0340 Camshaft position (CMP) sensor A, bank 1 circuit malfunction
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Wiring, CMP sensor, ECM

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Table of Contents

  1. What Does Code P0340 Mean?
  2. What are the common causes of code P0340?
  3. What are the symptoms of code P0340?
  4. How do you troubleshoot code P0340?
  5. Codes Related to P0340
  6. Frequently Asked Questions
  7. Get Help with P0340

What Does Code P0340 Mean?

A properly running engine is essentially the precise timing of gasoline-fueled explosions. Depending on engine speed (RPM) and load the engine control unit (ECU) controls the timing and amount of fuel injection, timing of spark ignition, and in the case of engines with variable valve timing (VVT), intake- and exhaust-valve timing adjustments. The two main timing and position sensors used by the ECU are the crankshaft position sensor (often CKP) and camshaft position sensor (often CMP). If there are two banks on a VVT-equipped engine, then there will be two camshaft position sensors.

The camshaft position sensor reacts to a toothed wheel on the camshaft, which gives the ECU constant information on its speed and position. Of course, the CMP is located on the engine, usually somewhere on the cylinder head, so it transmits CMP data to the ECU using wires. If the ECU cannot detect a CMP signal, it will set DTC P0340 or DTC P0345 – Camshaft Position Sensor Circuit Malfunction. If your engine has only one CMP, such as an inline-four-cylinder, the only CMP code available is for Bank 1, P0340. On the other hand, V6 or V8 engines have two banks, Bank 1 and Bank 2, and would therefore have two CMPs, so DTC P0345 would refer to Bank 2.  Sensor A indicates that the malfunction is occurring with the camshaft position sensor circuit that pertains to the intake camshaft.  Sensor B codes pertain to the exhaust camshaft.


What are the common causes of code P0340?

Depending on year, make, and model, DTC P0340 or P0345 may have number of causes. Here are some of the most common.

  • Faulty Sensor – If the sensor coil is open or shorted, then it will generate no signal.
  • Poor Installation – A good CMP signal is highly dependent on placement. Generally, the sensor needs between 0.020” and 0.050” clearance to the reluctor ring or camshaft tooth. If the sensor is cocked to one side or not firmly seated, the clearance will be wrong and the signal will be too weak for the ECU to detect. If the reluctor ring is rubbing on the sensor, the signal will be distorted.
  • Ford Trucks / Mustang GT – An alternator phase problem, such as a blown diode or open coil, may cause so much electrical interference that the CMP signal gets distorted, causing a P0340 / P0345 DTC to set, among others, in spite of there being no actual problem with the CMP sensor or wiring.
  • Cars in Storage – If your car has been in storage for any length of time, rodents may find it a great nesting place. Unfortunately, while looking for nesting materials and cleaning house, these little critters might find your wiring offensive or even tasty, resulting in open circuit problems.
  • Older Cars – Over time, plastic and rubber tends to become brittle and less flexible, which can lead to connector breakage and wire insulation damage. In turn, this may cause corrosion, open circuits, or short circuits.

Generally, the camshaft position sensor is pretty resilient and long-lived, which doesn’t necessary rule it out as a problem, but most of the time, the problem lies in the wiring and connectors for the sensor, or something else entirely. Before you just jump right on a new sensor, make sure you can rule out the rest of the system, first.

What are the symptoms of code P0340?

Because the CMP signal is so critical to ignition and fuel injection, you may experience a no-start or start-stall condition. Some vehicle ECUs may be able to use the CKP signal to estimate camshaft position, so the engine will run, but may experience hard starting, rough running, misfiring, or poor acceleration.



How do you troubleshoot code P0340?

Because P0340 and P0345 refer to a circuit problem, do not automatically condemn the CMP sensor. That’s not to say that it might not be the sensor itself, but replacing the sensor is not always going to fix the problem. Go to All Data DIY or other source and get out your wiring diagram and DVOM (digital volt-ohm meter) for this next part.

  1. Visual Inspection – At the CMP sensor, make sure it is plugged in and firmly seated. Also, follow the wiring harness to look for damage, such as from recent engine repairs, aftermarket installations, impact damage, or rodent damage.
  2. Sensor Inspection
    1. Resistance Check – Disconnect the sensor and measure resistance. An open-circuit, ∞ Ω, or short-circuit, 0 Ω, at this point would tell you that the sensor itself is at fault.
    2. Signal Check – The proper way to do this would be with a digital oscilloscope, but you can get a rough estimation of CMP sensor function by putting your DVOM in AC V mode. When cranking, you should be able to see at least 20 mV.
  3. Electrical Inspection – Disconnect the ECM and CMP connectors, and put a short pin across the terminals of the CMP connection. You can use a small paperclip or wire for this.
    1. From the ECM side, check for resistance in the circuit itself. With the short pin in place, you should read less than 0.1 Ω. Any higher, and the ECU will be unable to detect the signal. Look for a broken wire or corrosion somewhere in the circuit.
    2. Remove the short pin and check for open circuit, ∞ Ω. If there is some amount of resistance, suspect a short circuit. Water in an intermediary connector could easily be the cause of a short-circuit.
    3. Check for short-to-ground by taking one of the leads and connecting it to body-ground or the negative battery terminal. You should read an open circuit, ∞ Ω. Any unintentional connection to ground could distort or weaken the signal.
  4. Other Problems – In case no problems can be found in the CMP sensor or its wiring, it may be that P0340 or P0345 are simply auxiliary fault codes. A jumped timing belt, faulty crankshaft position sensor signal or circuit, or engine misfire, may be the primary problem. Double check these before coming back to the CMP.



DTC P0340 or P0345 may be accompanied by other DTCs, such as P0300 Random Misfire, P0725 Engine Speed Sensor Circuit, or P0335 Crankshaft Position Sensor Circuit Malfunction.

Frequently Asked Questions

How much does it cost to fix P0340?

First, what is a P0340? It’s the fault code that points to a failed camshaft position sensor or its related electrical circuitry. To repair, we will need to diagnose the problem first. Shops will typically charge no less than 1-hour labor to diagnose. This alone will cost anywhere from $120 – $150. If the sensor alone has failed, then we tack on the charge to replace the sensor and the cost of the sensor itself. Depending on the difficulty of replacement this will add anywhere from $120 to over $300. Also, in some cases, the only option is to go back to the dealer for the sensor. This typically increases the costs. If the sensor is easy to reach and the aftermarket has good replacement sensors, the total cost could be around $300 to diagnose and repair a P0340.

Can a bad crankshaft sensor cause a P0340 code?

It is possible that a failed crankshaft position sensor can have an associated P0340 code with it. Usually, you will have a fault code P0335 or P0336 for the crank sensor, depending on the issue. And diagnosis will usually have you test the crank sensor first. Possible, but rarely does the crank sensor set a P0340 code alone. A fault code P0016 thru P0019 may also be present if there is an issue with the cam position sensor/crank position sensor correlation. This means that there is a problem with the cam sensor and crank sensor patterns not matching up. You often see this on engines where the camshaft timing is out of sync with crankshaft timing.

What happens if you don't fix your camshaft sensor?

What happens? Depends on the year and manufacturer of your vehicle. If you have an older model (generally before 2010) you will probably find out that when the cam sensor fails, it will set a check engine light and keep running. However, when you shut the engine off, it will fail to restart. The only way to get it to restart is to replace the cam sensor. With newer models (anything after 2010) the engine controller can determine the cam position based on the crank sensor. So as long as the crank sensor is working, you only get a check engine light, but performance and fuel economy will be much lower. Wasn’t designed to run forever without a cam sensor.

Can you clean a camshaft sensor?

Sure. Just not sure if it will do any good.

Depending on the failure, cleaning a broke sensor won’t fix it. Kind of like adding thick oil to improve compression on a worn-out engine. Doesn’t fix the actual problem; may do absolutely nothing to improve the situation, and you’ve spent the time and money cleaning it. If the P0340 is set, it usually means the sensor or related circuitry has failed. The only time cleaning might help is if the sensor electrical connections are dirty and can use cleaning to improve the connection.

Can a camshaft sensor reset itself?

If the issue is within the cam sensor itself, it usually doesn’t “reset” itself. It usually sets the associated cam sensor code and has permanently failed. If the sensor has become “heat sensitive” it can fail when hot, but as soon as the sensor cools, it will start functioning again. The result is the same, which is replacing the failed sensor.

Do camshaft sensors have a fuse?

Cam sensors do not have a fuse, but the engine control system has several to protect the engine controller from failure, both internal to the controller and external inside the fuse box. Internal ones can reset automatically once the issue is resolved. This has been true since the late 1980s / early 1990s.

Do you need to relearn a camshaft position sensor?

Most are designed to be “plug and play”. Meaning you put them in and they work without any other intervention. Others will need to be “calibrated” to the engine/engine control system. Gm had several engines that required this, as well as some Chrysler products. Service information will inform those replacing the sensor when it requires a relearning / recalibration procedure.

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