7 Symptoms of a Bad Camshaft Position Sensor (and Replacement Cost in 2022)

7 Symptoms of a Bad Camshaft Position Sensor (and Replacement Cost in 2022)

How It Works

The camshaft position sensor, also known as the cylinder recognition sensor is a magnetic device that works to report the position of the camshaft to the engine control module via an electrical connection. The sensor is typically positioned in line with the camshaft gears to closely monitor and obtain the rotational data. 

The device uses a magnetic resistance element to sense the changes happening at the camshaft teeth and understand rotation speeds, stimulating an AC voltage to be transmitted to the computer.

When the teeth around the sensor rotate, they stimulate a change in the pulse which is used to produce an AC voltage reading.

The voltage sent to the ECU. The frequency and number of the pulses helps the system precisely determine how fast the pistons are moving and where they are currently located.

IV. CMP Codes and What They Mean

Common CMP Trouble CodesSource of Trouble

P0340 CMP

Circuit malfunction

P0341 CMP

Circuit range or performance problem

P0342 CMP

Circuit low input

P0343 CMP

Circuit high input

P0344 CMP

Circuit intermittent


Symptoms of bad camshaft sensors

The camshaft sensor is a part of the engine’

The camshaft sensor is a part of the engine’s timing system. If the sensor is defective, it will affect the way the engine operates and behaves. Bad sensors will cause the engine to misfire, backfire, or lose power. Faulty cam sensors will also trigger the Check Engine light, and the computer will set the vehicle to fail-safe mode.

Check Engine light

The cam position sensor is one of the sensors that trigger the Check Engine warning when it goes bad. The camshaft position sensor works in conjunction with other sensors in the engine. If one or more of the sensors is faulty (like the cam sensor), it will send out a warning in the check engine light.


Engine misfire is a sign associated with bad cam sensors. If the sensor is worn, it may not provide the computer with the correct camshaft position. This causes the computer to determine timings based on faulty input from the sensor. The computer will then send out unoptimized timing signals to the injectors and ignition coils, causing the engine to misfire.


Engine backfire is another sign of worn cam sensors. Like misfires, improper timings cause the engine to backfire. If the timing is off, the air/fuel mixture will leave the combustion chamber unburnt. This unburnt mixture may combust in the exhaust system due to the exhaust manifold and exhaust pipes’ heat.

Struggling, stalling, or trouble starting

Engine struggling or stalling is another sign that the camshaft sensor is bad. Faulty inputs from the sensor will cause the computer to retard or advance the timings needlessly. Bad sensors will also cause the valves to open too early or too late. This deprives the engine with the correct amount of air needed for efficient combustion, resulting in a loss of engine power.

Shifting issues

Modern vehicles come with a fail-safe safety feature called the “limp mode.” The car computer activates the feature if it detects a fault (such as a bad camshaft sensor) in the engine. When the vehicle is under the limp mode, you won’t be able to shift beyond the second gear and speed up your vehicle. 

I. A Camshaft Position Sensor Can Fail Without Warning

An intermittent or complete CMP sensor failure while on the road could be dangerous. It could happen at any time: You are driving on the highway, moving along in fast traffic, when your engine suddenly loses power. There is nothing to do but watch in horror as a vehicle approaching at 70 miles an hour rear-ends you. Not a pretty picture, but it's happened many times.

Other times the driver becomes aware of a failed CMP sensor when the engine refuses to start.

Here, we'll explore the symptoms of a bad camshaft position sensor and what you can do about it. But let's discuss first what the sensor does.

6. Increased Emissions

A badly running engine won’t be burning fuel as efficiently or may be running rich. This will lead to increased emissions and can damage the catalytic converter if left unresolved.

How Does A Camshaft Position Sensor Work?

Camshaft Position Sensors use the same electronic principles of other engine sensors such as Crankshaft Position Sensors.

In other words, they are so similar in construction they are often difficult to differentiate from one another when outside the vehicle.

There are two common types of sensors. The design can be based on “optical”, “inductive”, or “Hall Effect” principles. For the purpose of this article, we will explain the Hall Effect design.

Hall Effect sensors consist of two key elements, the reluctor ring (toothed wheel) and the sensor itself which internally has a permanent magnet.

The reluctor is attached to the camshaft in a way that cylinder #1 intake valve opening coincides with the “tooth”.

Many designs include all cylinders (not only cylinder #1) but using a wider tooth for differentiating #1 which will always be the “reference”.

As the camshaft rotates the permanent magnet inside the sensor will induce an electrical current each time the tooth aligns with it. The Hall sensor signal produced this way is similar to a square waveform like the green like shown below: 

The ECU uses this information for the fuel injectors “firing” sequence, thus the importance of an accurate reading.

As said earlier, independently of the Camshaft Position Sensor design (single tooth or multi-tooth) the Camshaft Position Sensor and Crankshaft Position Sensor signals are always compared and used together not only for fuel delivery but also for ignition timing and spark plug firing.

Black Exhaust Smokes

In addition to rough idles and misfires, incorrect timings and duration for fuel injection can also lead to black smoke from the tailpipe.  A bad camshaft sensor can indirectly dump unburned fuel into the exhaust that not only affects the fuel economy but can produce some disquieting black smoke from the tailpipe.

When the timing for fuel injectors is not optimal, they may sometimes fire an immoderate amount into one cylinder which is forced down the exhaust to be burned. Such fuel that is not burned in the combustion chambers comes out black smoke. 

How to tell which camshaft sensor is bad?

You can tell which camshaft sensor is bad by using the above method that entails a multimeter. You may also unplug the sensors to take a look at the physical damage, any corrosion, or deposits that are not supposed to be present. 

The signs and symptoms that are associated with a faulty camshaft are also a clear way to pinpoint the issue. The check engine light will be able to notify you of the problem and you can use the OBD 2 scan tools to check for the specific trouble codes. The manufacturer-specific codes will be able to notify you if the issue is in the sensor or the associated circuit. 

How to replace a faulty cam position sensor?

If you decide to change the sensor yourself, follo

If you decide to change the sensor yourself, follow these simple steps:

  • Park your vehicle on a flat and even surface.
  • Turn off the engine.
  • Remove the negative (black) battery cable from its terminal on the battery.
  • Locate the camshaft position sensor around the engine’s cylinder head. If you are having trouble, check your manual.
  • Unplug the connector from the sensor.
  • Remove the sensor from the cylinder head. The sensors are usually secured by bolts.
  • Install the new cam position sensor.
  • Reinstall the sensor connector.
  • Reconnect the black battery cable to its corresponding terminal.
  • Start the engine and check if the Check Engine light is lit.
  • If there is no Check Engine light warning, take your vehicle for a test drive.
  • If the engine is running well, congrats, the replacement is successful!

Symptoms Of A Bad Camshaft Position Sensor

As a camshaft position sensor plays an important r

As a camshaft position sensor plays an important role, many issues can arise if it is bad.

The most common symptoms that occur are the following:

  • Check engine light
  • Stalled engine
  • Unable to start the car
  • Rough idle
  • Reduced engine power
  • Bad gas mileage

All these symptoms may appear individually or together. In most cases, the check engine light will illuminate alongside one or more of the symptoms.

In the text below, each of the symptoms listed will be explained so you can get a clearer picture of the problem affecting the camshaft position sensor.

Check Engine Light

The most common symptom of a bad camshaft position

The most common symptom of a bad camshaft position sensor is the appearance of a check engine light.

As always, when the light comes on, it will probably be unclear what the problem is. In order to get a clearer picture, you should scan your car for any error codes with an OBD2 scanner.

If you do not have an OBD2 scanner, you should take your car to a mechanic. If you can avoid it, you should not drive your car if the light illuminates, as more damage could be done.

If you know the cause of the check engine light, you might be able to drive the car to the shop, provided that a professional mechanic or someone equally qualified has given you the green light.

In many cases, the so-called “limp mode” might engage. This is a safety feature that restricts the power and speed of your car to protect all its components.

Generally, you can drive your car to the nearest shop if the limp mode is engaged. Just like the check engine light, the limp mode might disappear when you turn your engine off and on again.

Stalled Engine

A more serious but thankfully rarer symptom is whe

A more serious but thankfully rarer symptom is when the engine stalls. This could happen when you are in a parking spot or when you are driving on the road.

The latter scenario can be extremely dangerous. If your engine stalls unexpectedly, do not drive the car at all.

This problem is caused when no combustion occurs as no fuel or air enters the combustion chamber at the right moment.

Unable To Start The Car

This symptom is related to the previous one. As th

This symptom is related to the previous one. As the sensor does not work optimally, the engine will have a hard time starting.

As with almost any other symptom, this could be due to a variety of reasons. Other reasons why a car won’t start might be due to a faulty starter, clogged fuel filter, dead battery, or other reasons.

Rough Idle

When everything is as it should be, a nice and ste

When everything is as it should be, a nice and steady idle will largely go unnoticed by the driver. However, when the idle is rough, it will be very noticeable while driving.

If the camshaft position sensor is faulty, the rough idle is due to the unsynchronous combustion taking place in the cylinders.  

A rough idle might also be a consequence of a faulty fuel pump or EGR valve. Whatever the cause, it is important to know what causes the rough idle. It may require some extra tools and testing to find out.

Driving with a Bad Camshaft Position Sensor

Although you can continue to drive with a bad sensor, we do not recommend that you do so. Continuing to drive the car can lead to additional failures in other areas of your car, which can end up causing you to have a higher service bill. Your car can also stall when the sensor is failing. This can be dangerous to you, your passengers, and everyone on the road.

What Are the Symptoms of a Bad or Failing Camshaft Position Sensor?

1. Check Engine Light Comes On

The most common indicator that the camshaft position sensor is failing is a lit Check Engine light.

OBD II (on-board diagnostics II) systems efficiently monitor vehicle hardware and software and can detect part deterioration that causes imperceptible performance changes before a part completely fails. Although you can connect to the ECM using a DIY scan tool to try and diagnose the problem, it’s best to take it to the pros when the Check Engine light illuminates. Ignoring the Check Engine light can lead to expensive engine or transmission repairs.

2. Poor Drivability

A failing camshaft position sensor begins losing its ability to quickly transfer data. Mismatched fuel delivery and ignition timing, even if off by a few milliseconds, will cause your vehicle to sputter, accelerate poorly, lack power, stall or even shut off.

3. Transmission Shifting Problems

Data received by the ECM from a failing camshaft position sensor can keep transmission shift solenoids from operating and gears from shifting. Called “limp-home-mode” on some models, it helps protect the engine from damage by restricting engine speed.

4. Bad Fuel Economy

Inaccurate camshaft position sensor data can keep fuel injectors open too long, forcing excess fuel into the combustion chamber. This also can cause engine knocking and serious damage if too much liquid gasoline (which does not compress) builds up in the combustion chamber.

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