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Symptoms of a Bad Camshaft Position Sensor

Updated on May 20, 2017
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

A failing camshaft position sensor (CMP sensor) can produce a confusing range of problems, depending on the way it fails and the model of the car:

  • Transmission locking in a single gear until you turn it off and restart
  • Car jerking and losing power
  • Loss of engine power; for example, no acceleration above 35 mph
  • Stalling
  • Irregular acceleration
  • Misfiring
  • Hard starting
  • Surging
  • No spark: no start at all

Camshaft position sensor
Camshaft position sensor | Source

A Camshaft Position Sensor Can Fail Without Warning

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 already happened many times. Hopefully not to you.

The culprit behind some of these accidents is a failed camshaft position sensor (CMP sensor). Sometimes a CMP sensor can fail without warning, causing the engine to shut off. Other times, the driver may be unaware of developing symptoms until 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.

What Is a Camshaft Position Sensor?

The camshaft controls the opening and closing of the intake and exhaust valves.
The camshaft controls the opening and closing of the intake and exhaust valves. | Source

Your engine's cylinder head houses one or two camshafts—a shaft equipped with offset lobes—to operate the intake and exhaust valves. The crankshaft, located in the engine block, drives the camshaft using gears, a timing chain, or a timing belt.

Camshaft | Source

To determine which cylinder is in its power stroke, your car's computer monitors the rotating position of the camshaft relative to the crankshaft position using a camshaft position (CMP) sensor. It uses this information to adjust the spark timing and the operation of the fuel injectors. Thus, the CMP sensor affects fuel economy, emissions control, and engine efficiency.

Camshaft position sensor (Hall-effect type)
Camshaft position sensor (Hall-effect type) | Source

The two most common camshaft sensors you'll see are the magnetic and Hall-effect types. Both transmit a voltage signal to an electronic control module or to the car's computer.

The magnetic type produces its own AC (alternate current) signal (a sine wave), and you can identify it by its two wires. The Hall-effect type uses an external power source to produce a digital signal (a "square wave," on-or-off) and has three wires.

Note: If you are new to all this, you should know that the camshaft position sensor is a different part from the crankshaft position sensor.

Symptoms of a Bad Camshaft Position Sensor

Just like every part or component in your car, the CMP sensor will eventually stop working when it's reached the end of its service life, because an internal part, wire, or related component has failed. The symptoms your engine may experience at this point can vary, depending on the type of sensor failure: for example, a problem in the circuit, the connector, the sensor itself, or a related component.

  • On some vehicles, a failing camshaft sensor may lock the transmission in a single gear until you turn off and restart the engine. This cycle may repeat intermittently.
  • If the sensor begins to fail while your car is moving, you may feel the car jerking while losing power.
  • You may experience a noticeable loss of engine power. For example, the engine can't accelerate above 35mph.
  • The engine may stall intermittently.
  • You may notice poor engine performance including irregular acceleration, misfiring, hard starting, or surging.
  • On some car models, a failed CMP sensor will prevent the ignition from making a spark, so that the engine won't start at all.

Once your car's computer detects a CMP sensor failure, it will trigger the engine light and store a diagnostic trouble code (DTC) in its memory (see the table below for common camshaft position sensor trouble diagnostic codes). An intermittent or complete CMP sensor failure while on the road could be dangerous.

CMP Codes and What They Mean

Common CMP Trouble Codes
Source 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

Camshaft Position Sensor Location


As you may expect, the specific location of the camshaft position sensor varies by a vehicle's make and model. On most models you can find the sensor somewhere around the cylinder head. Look around the top section of the timing belt/chain cover (in the front of the engine) or at the rear end of the cylinder head. Some GM models may have a special compartment for the sensor.

Also, some Mercury Villager and Nissan Quest models locate the CMP sensor inside the distributor housing, as well as some Dodge Ram B1500, B2500, and B3500 series models with gasoline engines.

Depending on the specific model of your car, your engine may have one or more cam sensors.

If you need help finding the sensor(s), check the vehicle service manual for your particular model. You may find a copy in the reference section of your local public library. I highly recommend that you buy an aftermarket repair manual for your specific vehicle make and model (Haynes is a good inexpensive brand) for reference when doing maintenance and small repairs.

CMP Sensor Troubleshooting

If your car computer has already triggered the engine light, you may retrieve the code (the DTC) using a code reader or a relatively inexpensive scan tool. If you don't own a code reader and can't afford to buy one, and you still can drive your car safely, just go to a nearby auto parts store that retrieves DTCs for free.

After confirming a CMP-sensor related trouble code, it's worth doing some simple tests. A trouble code pointing to a potential CMP sensor failure doesn't necessarily mean that the sensor itself is bad. You may be dealing with a wire, connector, or related component failure that you can fix yourself.

However, confirming the good or bad operation of a camshaft sensor may require a scope. A failing sensor signal, for example, may be hard to check without special equipment. Still, you can do some simple checks in your garage using a digital multimeter (DMM) tool.

  • First, check the condition of the sensor's electrical connector and wires. Unplug the connector and check for rust or contamination, like oil, that is interfering with good electrical contact. Then check for wire damage: broken wires, loose wires, and signs of burns caused by nearby hot surfaces. Also, make sure the sensor wires are not touching spark plug wires or ignition coils, which may interfere with the sensor's signal.
  • After these checks, use a digital multimeter that can test either alternate current (AC) voltage or direct current (DC) voltage, depending on your particular type of camshaft position sensor. You'll also need the correct electrical values for your particular type of sensor. You may find this information in your vehicle repair manual.
  • With some sensors, you may back-probe the wires through the sensor electrical connector.
  • If this isn't possible, see if you can unplug the sensor connector and attach a strand of copper wire to each terminal on the connector. Then plug the connector back in so that the two strands stick out through the connector's housing.
  • Another testing solution is to pierce through each wire using a pin, being careful not to short out the wires during your tests. If you use this last method, use electrical tape to cover the pin holes on the wires' insulation after you're done with your tests to prevent corrosion from creeping into the wires.

Testing a Two-Wire Sensor:

  • If you have a two-wire, magnetic-type CMP sensor, set your multimeter to "AC volts."
  • Have an assistant turn the ignition key on without starting the engine.
  • Check for the presence of power flowing through the circuit. Touch one of your probes to ground (any metal part on the engine) and the other probe to each one of the sensor wires. If neither wire has current, there's a failure in the sensor's circuit.
  • Have your assistant crank or start the engine.
  • Touch one of your meter probes to either one of the sensor wires and the other probe to the other wire. Check your meter display and compare your reading to your manual specifications. In most cases, you'll see a fluctuating signal between 0.3 volts and 1 volt.
  • If there's no signal, you have a bad CMP sensor.

Testing a Three-Wire Sensor:

  • Once you identify the power, ground, and signal wires using your vehicle repair manual, test the sensor's circuit by setting your multimeter to "DC volts."
  • Have an assistant turn the ignition key on, but don't start the engine.
  • Touch the black probe on your meter to ground (a metal bracket, bolt, or metal surface on the engine itself) and the other probe to the power wire. Compare your reading to the specification in your manual.
  • Have your assistant crank or start the engine.
  • Touch the signal wire with the red probe from your meter and the ground wire with the black probe. Compare your reading to the specification in your vehicle repair manual. If the voltage signal is lower than the specification, or no signal comes out of the sensor, most likely the sensor is bad.
  • Remove the sensor and inspect it for signs of physical damage or contamination.

Check the video below to see how you can perform these tests using a test light and a multimeter. It'll give you an idea of the nature of the tests too. If you can't find anything wrong with the sensor or its circuit, it's possible you may have an intermittent failure or a failure in a related component. For example, you may have a weakened or overstretched timing belt or timing belt tensioner. A worn-out belt can prevent the camshaft and crankshaft from synchronizing, causing the CMP sensor to send the wrong signal.

Testing a Camshaft Position Sensor

Sensor Replacement and Cost

If you've confirmed that the camshaft position sensor is bad, you may want to replace it yourself. On some vehicle models, replacing the sensor is just as easy as unplugging the electrical connector, unscrewing the mounting bolt, pulling the sensor out, and installing a new one. On other models you may need to remove one or more components to gain access to the sensor (as you will see in the next video).

Check your car's repair manual for instructions on how to replace the sensor on your particular vehicle model.

Expect to spend anywhere between $30 and $100 (or more) for the sensor itself, depending on your vehicle model. If you take your vehicle to a car shop, you may be looking at $100 or more in labor expenses too.

Replacing a Camshaft Sensor (Nissan Altima)

The symptoms I discussed above are not clear signs that your CMP sensor is bad. Still, if you recognize one or more of these symptoms, try to diagnose the problem as soon as possible. The last thing you want is to get stuck in the middle of the road. Start by getting the trouble codes from your computer memory, and, if necessary, testing the sensor with the help of your vehicle service manual. Sometimes you can determine the cause of the problem and fix it yourself without spending too much time and money.

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    • Mark Johann profile image

      Mark Johann 2 years ago from Italy

      I am new to this and it will help me install it someday. I did not know about this kind of camshaft sensor before. This is a great help for motorists who are not that expert in automotive to help them determine malfunctions inside an engine.

    • ttrimm profile image

      ttrimm 22 months ago

      Hi. just wanted to say that it's totally awesome that you are using my photos. We had to replace both of them when we did this!

    • Dan Ferrell profile image

      Dan Ferrell 22 months ago

      Hi ttrimm, thanks for posting and making the photos available. They were just perfect for the article. And glad to hear you were able to replace both cmp's without any problems.

    • profile image

      D Moore 21 months ago

      What can you do if the connector itself is bad on the rear cam sensor on a 2004 Nissan Quest?

    • profile image

      amanda 10 months ago

      Hi I have a 2012 lancer mitsubishi ES an i can't fie the camshaft to replace it can you help me thank u

    • profile image

      Rachel 9 months ago

      2005 terracan won't start. Ticks over but doesn't crank over to start. Need help please!

    • Dan Ferrell profile image

      Dan Ferrell 9 months ago

      Hi Rachel,

      Do you have enough battery power? Also, check the starter solenoid.

      I'd start with these two.

      Good luck

    • profile image

      Danny 8 months ago

      Hi, After driving my car for 30 minutes my car loses power and revs fly high and can just limp along. My cars been out of action for 18 months with this problem. I live in the tropics and unfortunately I cant find a decent mechanic. Does anyone think this could be the crank/camshaft sensors? Please help!

    • Dan Ferrell profile image

      Dan Ferrell 8 months ago

      Hi Danny,

      Have you scanned the computer for any DTCs? That would be a good start. From what you describe it seems your fuel pump or ignition coil are having some problems, but that's hard to tell without getting some info from the computer. Any of the sensors may be also at fault.

      If there's an auto parts store you can get to and have them scan the computer, get the codes and see what happens.

      Good luck.

    • profile image

      Cesar 8 months ago

      Hello There,

      -It seems I replaced the CAM sensor with a CRANKSHAFT sensor. Are there any potential problems?

    • profile image

      Bud 8 months ago

      Hi, I have a 2011 Subaru Outback w/ a 3.6L (6 cyl) boxer.

      How likely is it to have an OBDll trouble code of p0011 & p0021 plus p0420 which indicates both L&R CMP throwing a failure code. Also the p0420 (catalyst sys. below threshold). Can these codes be related? I have been scratching my head over this. I do have a 2011 Subaru service/ repair manual on CD, I can not find the ohm value for the intake cam sensor. Is there a way to test it's value , or in other words is there a range I should be looking for? BTW my car has all the symptoms you described in your post "Symptoms of a bad camshaft position sensor. Thanks in advance, Bud

    • profile image

      Sunny 7 months ago

      I have a 97 Mitsubishi marage deluxe (standard)

      I chose to use the freeway which i never use; i always go thru town, but i got up to about 60 in 5th gear, and my car started to overheat my foot was to the floor board trying to keep up to freeway speed and keeping in mind that the pedal was floored; the speedometer kept going down, i was loosing speed in fifth with the pedal to the floor, white smoke started coming thru the vents as i turned the fan on to try and cool it down a little,

      So white smoke was coming from the engine, and also it didnt make any crazy noises either and there wasnt any black smoke so i font think its blown, it turns over but theres hardly any compression from what i could feel when i put my finger in the spark plug hole as my friend turned it over, soo no combustion?

      My friend said a snapped camshaft, at first i thought the engine seized, and then a blown head gasket made more applyable sense because theres water in the oil im pretty sure, i took the plugs out and turned it over to try and flush what ever was in the piston bays out do it would start, assuming it had water/voolant

    • Dan Ferrell profile image

      Dan Ferrell 7 months ago

      Hi Sunny,

      You might be right. It sounds like you got a blown head gasket. The white smoke and lack of compression seem to point in that direction. Do a compression test. Hopefully you were able to stop the engine before any major damage occurred.

      Good luck.

    • Dan Ferrell profile image

      Dan Ferrell 7 months ago

      Hi Bud,

      I don't have those values with me either. But the codes could be related if the computer went into limp mode and is operating under a standard value to compensate. So the O2 sensor may be registering out of range. If you can't find the ohm values for your cmp sensors with a little search online, head over to

      and ask for the CMP values for your application. They are more likely to help you with it.

      Good luck.

    • profile image

      Andy 7 months ago


      On the 2001-2007 Dodge Caravans and Chrysler Town and Countrys, if you turn the ignition on/off/on/off/on (not actually starting engine) quickly, where the mileage is displayed it will give you the diagnostic code then say done. If there is more than oe code it will give you the codes one at a time and then say done.

    • profile image

      Dilly 6 months ago

      I have a 2006 dodge charger and after so many miles of riding my car will just cut off in mid drive as if it's out of gas... I have to let it sit for about 30mins then it will crank back up... Someone told me that it sounds like the fuel pump is getting to hot... I don't know.... What do you think?

    • profile image

      Charles1990 6 months ago

      I have an 99 Tahoe and I turned the key the truck won't turn on at all I have power and fuel what do you think it might be plus wen I turned key radio turns off. Not my head lights

    • Dan Ferrell profile image

      Dan Ferrell 6 months ago

      Hi Charles,

      It seems from what you describe that your ignition switch might be bad, need to check it first; also check the starting circuit for a bad connection (including the battery -have it checked at an auto parts store, minimum).

      Good luck

    • profile image

      Chrystal Slonecker 6 months ago

      I have my 2004 quest at shop. They just to told me the problem with it, is this- $515.00 to that reasonable?

    • Dan Ferrell profile image

      Dan Ferrell 6 months ago

      Hi Chrystal

      That depends on the repair (labor) plus what parts they're going to replace. You can check at RepairPal.

      Good luck.

    • profile image

      Chris Hammac 6 months ago

      I have a 2003 Ford Escape XLT with a crank/no start condition. I've checked fuel, spark and compression. All are present. I installed a new crankshaft position sensor but I noticed that when I turn the motor over, it only shows rotation on the tachometer occasionally. That seems to be when the motor actually sounds like it wants to start. What could be causing the intermittent rotation issue? Is there something else I should be looking at?

    • Dan Ferrell profile image

      Dan Ferrell 5 months ago

      Hi Chris,

      Did you check fuel pressure and volume? Compare your figures to specs for your specific model- you can find them in your repair manual.

      This other article might be of help too:

      Good luck.

    • profile image

      James Lang 5 months ago

      I have a 1999 chev. Blazer and my CAMSHAFT POSITION SENSOR is located in the Distributor cap! I seen videos of people just changing them, but some people say that it should be relearn first! Can you give me some insight?

    • Dan Ferrell profile image

      Dan Ferrell 5 months ago

      Hi James,

      The procedure is not that complicated, but you may want to check the repair manual for your make and model. You can find inexpensive manuals in amazon. The investment will pay for itself after your first maintenance/repair like replacing the CPS.

      Good luck.

    • profile image

      Grizzly 5 months ago

      Would a starting to fail sensor cause lean codes when stalling. Have checked all other causes of lean code but nothin. Could this be the problem with Ford engine stall problem with lean codes that no one can figure out.

    • profile image

      Thomas Falater 4 months ago

      This happened to my Mercedes and I checked the wires, did all the tests, and replaced my camshaft position sensor with a $30 one. Two days later the check engine light came on with the same error message 'camshaft position sensor', although the engine ran fine. I bought a Bosch brand position sensor for $100 and installed that and it solved the problem. The check engine light stayed off. Don't buy the cheap sensors. Thomas Falater

    • Dan Ferrell profile image

      Dan Ferrell 4 months ago

      Hi Thomas,

      Yes, usually on electronic components try to buy brand quality replacement or OEM. You'll save yourself from a lot of trouble, even if you spend a little more.

      Glad to hear the car is back on the road.

      Good luck.

    • profile image

      KellyT 4 months ago

      Hello, I replaced my Camshaft Sensor as my engine light came on and the code said it was the sensor. However, after driving it for a few days, the engine light came back on... Camshaft sensor again. What could cause this? Also, my gas cap doesn't click anymore... could this also cause my engine light to come on??? Thanks in advance for any help!

    • Dan Ferrell profile image

      Dan Ferrell 4 months ago

      Hi Kelly,

      When your car computer stores a DTC (diagnostic trouble code), it only points to the circuit where it detected a poetntial malfunction. In this case, the camshaft sensor circuit. It doesn't necessarily meand the sensor itself is bad. You still need to verify whether the sensor is bad, or the circuit that makes the sensor work. You need to troubleshoot the circuit and the sensor to see where the fault is located.

      If the gas cap is not closing tight, yes, it could trigger the check engine light. You might want to replace the cap with a new one and then check to see if the light goes on. Otherwise, have the sensor and circuit checked.

      Good luck.

    • Dan Ferrell profile image

      Dan Ferrell 4 months ago

      Hi Dilly,

      Sometimes when a pump is on the way out, it'll cut out after a few minutes of driving. And the same thing happens some times with the ignition control module. Let them cool down and they'll come back to life. It can drive you crazy. But after some time, they'll just die.

      (Sorry for the late response - the comment was wrongly cut by the spam detection robot)

      Good luck

    • Dan Ferrell profile image

      Dan Ferrell 4 months ago

      Hi Grizzly,

      There could be seeral reasons for a lean code, if you're not getting a specific circuit malfunction DTC from the computer, check for a possible vacuum leak, dirty MAF sensor, and also check the air filter housing and assembly for a leak after the MAF sensor (unmetered air).

      When was the last time you changed the fuel filter (every year or two is the most recommended) a clogging filter can give you this type of problem.

      (Sorry for the late response, your comment was wrongly caught by the spam detector"

      Good luck

    • profile image

      Fahad 4 months ago

      HI, i have been looking for the soulutin for my Audi TT 1.8 coupe 2003 A/T..

      i bought this car whit engine light ON, i did scan and the code i forgot, cause it was long time ago and car was still running.. i cleared the code and it cam back after next start.. later on it becomes difficult to start the car sometimes, after 2,3 cranks it get starts... i kept it driving this way.. i remember it went off once while driving.. but usually i had trouble to start the car in one self... i parked this car for few months.. batter went dead and car didnt started again.. i changed the battery still its cranking but not starting up... anybody has any idea??

      i am about to replace camshaft position sensor and crank sensor soon because on youtube and other sites recommends things like this happen if one of these sensors are not working..

      by the way i did the scan again last week it was code P017 something i cleared the code but because i cant start the car i dont know what was the code for...i cant see any code unless the car starts again..its on but no error until it gets starts..(my bad)

      what are your suggestions??


    • profile image

      Dam 4 months ago

      On a 98 ford explore V6 does the camshaft positioning sensor control The fuel injectors? I'm getting fuel when I turn the key on when I crank the motor fuel pump is not pumping in my Fuel injectors aer not pulsing?

    • Dan Ferrell profile image

      Dan Ferrell 4 months ago

      Hi Dam

      Yes, the CMP sends a pulse signal to the computer when cylinder 1 is about to reach TDC on the compression. This is to synchronize and sequence the injectors.

      Have you check for any computer trouble codes? If you get a code for the CMP, first check it to make sure the sensor is the one causing trouble, then check the circuit (connectors and wires) betwen the sensor and the computer.

      Good luck.

    • profile image 3 months ago

      hi i am working on a toyota 3rz engine , cylinder no 4 is not contributing any power to the engine what can cause that. all valves are closing the compression is ok . the ht lead is supplying the spark . but when i pull out the ht leadf it shows there is no contribution

    • Dan Ferrell profile image

      Dan Ferrell 3 months ago

      Hi nyasha

      Have you checked for a spark leak? Also, check the boot and the spark plug to see in which condition they are. Make sure four cylinder wire is receiving the command from the computer to fire.

      Good luck

    • profile image

      patricia 2 months ago

      having issues with my car passing emissions it is saying cam shaft sensor out of timing and also speed senor just replaced valve cover and new plugs this didn't arise until we done this

    • Dan Ferrell profile image

      Dan Ferrell 2 months ago

      Hi Patricia,

      Can be just coincidence, but your mechanic should be able to test the sensors to make sure they are working correctly before replacing them. Maybe something got disconnected during the service procedure that trigger the engine light.

      Good luck.

    • profile image

      adnan 4 weeks ago


    • profile image

      Pat Taillon 3 days ago

      2003 Cadillac cts. Turned the key and vehicle to seconds after releasing key to start. Approx 3 simular starts within an hour the check engine light came on. Took to auto store for diagnosis code P0343 showed up. Camshaft position sensor A Circuit high input B1 reading. Hoping for opinion on sensor or cause that would trigger sensor. Thanks in advance. Pat

    • Dan Ferrell profile image

      Dan Ferrell 2 days ago

      Hi Pat,

      Apparently you have a fault in the circuit, check the wires that connect to the sensor for cuts or damage. If you feel comfortable using a digital multimeter, test for ground, power and signal voltage to the sensor. The problems seems to be more likely in the circuit. But don't discard a faulty sensor.

      Testing will be easier if you have the repair manual for your car make and model. You can find relatively inexpensive aftermarket manuals at Amazon and your local auto parts store.

      Good luck.

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