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Symptoms of a Bad Camshaft Position Sensor

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

A failing camshaft position sensor (CMP sensor) can produce a confusing range of problems.

A failing camshaft position sensor (CMP sensor) can produce a confusing range of problems.

Problems That Can Be Caused by a Failing Camshaft Position Sensor

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:

  • 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.

I. A Camshaft Position Sensor Can Fail Without Warning

II. What Is a Camshaft Position Sensor?

III. How the Sensor Can Fail

IV. CMP Codes and What They Mean

V. Camshaft Position Sensor Location

VI. CMP Sensor Troubleshooting

VII. Video: Testing a Camshaft Position Sensor

VIII. What If My CMP Sensor Seems to Be Working Find?

IX. Sensor Replacement and Cost

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.

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.

II. What Is a Camshaft Position Sensor?

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.

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)

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.

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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.

III. How the Sensor Can Fail

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.

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).

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

V. 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.

VI. 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.

VIII. What If My CMP Sensor Seems to Be Working Fine?

If it seems your CMP sensor is working correctly, consider these possibilities.

Fuel injectors not firing:

In many vehicle models, the car computer uses the CMP sensor signal to fire the fuel injectors.

If you've determined that your engine has spark but fuel injectors are not firing, there's a chance your CMP sensor has failed.

CMP Sensor internal circuit malfunction:

It's not uncommon for a CMP sensor's internal circuitry to develop an electrical open. This is usually caused by the sensor being exposed to engine high operating temperatures.

High temperatures can break a wire. The broken wire may still make contact while the engine is cool. As soon as the engine compartment temperature increases, the damaged wire may expand and separate, creating an intermittent failure.

Faulty timing belt or chain:

If your tests seem inconclusive, especially if the problem has triggered a CMP sensor-related trouble code, you may want to check your timing belt or chain.

Timing belts (not so much timing chains) will stretch after miles of hard work, and tensioners will wear out over time, upsetting spark timing.

This will not only show the symptoms of a bad camshaft sensor but even trigger a CMP sensor-related trouble code.

Some car manufacturers suggest replacing a timing belt and tensioner every five years for this reason.

If necessary, consult the vehicle repair manual for your particular vehicle make and model.

IX. 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.

Let's Recap

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.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

Question: Can a faulty camshaft sensor cause a knocking sound?

Answer: No, a faulty camshaft sensor can't cause a knocking sound unless it affects ignition timing.

Question: Can a faulty camshaft sensor cause a P0300 code?

Answer: A number of faulty components may trigger a P0300 code, including:

a bad camshaft position sensor

bad spark plugs or wires

problems with an exhaust valve

bad fuel injector

bad ignition coil

bad oxygen sensor

blocked or inoperative EGR valve

Question: What is code P0340 on my Camshaft Position Sensor?

Answer: The code points to a fault in the camshaft position sensor circuit.

Question: I found metal shavings on one of the camshaft position sensors. Does this mean the motor is junk?

Answer: It’s ‘normal’ for camshaft and crankshafts to collect some filings. The magnets pick this up. It’s part of the normal wear and tear, although sometimes this indicate damaged metal parts.

Question: What does code P054A and P054B mean related to a camshaft position sensor?

Answer: P054A - the computer has detected that timing for the VVT is too advanced. P054B is the opposite - the ECU has detected that timing for the VVT is retarded too much.

Question: I have a 2009 Sonata 3.3 V-6. Would a faulty crankshaft position sensor cause the engine to crank over without starting?

Answer: Yes, it's possible, if the sensor is not sending the proper signal or there are problems in the circuit. This other post may help:

Question: When I measure the ground wire on my CMP I get a lower reading than when I ground on the block. Is this a problem?

Answer: There could be a bad ground on the sensor. Check it first with the ignition in On, and using engine ground. Then, crank or start the engine and check with the sensor ground. Compare your reading to specs. This will give you a batter indication of the condition of the sensor.

Question: My 2011 Altima is letting out white smoke and is needing oil depending on how much miles I run it. Now, the computer just came up with the camshaft position sensor. Is that sensor whys it's doing that?

Answer: The CAM tells the computer the position of the camshaft, and works in sync with the crankshaft sensor, so the computer knows when to fire an injector (depending on model) and to fire spark. The white smoke is more related to coolant or oil leaks (bluish smoke) into the combustion chamber. So most likely there's a leak at the cylinder wall, rings, valve or head gasket. You may need a compression test and leak down test to diagnose the problem.

Question: What causes the P1345 code in a Mazda 323?

Answer: The code points to the camshaft position sensor. There could be a faulty sensor or circuit (wire, connector, harness).

Question: Can the camshaft sensors go out without the check engine light coming on?

Answer: Usually, if the sensor starts wearing out, the computer may not turn on the check engine light, or if the fault is intermittent. But once the PCM detects a problem with the sensor or the circuit, the engine light will come on.

Question: Can a faulty camshaft position sensor cause smoke to come out of your exhaust?

Answer: It is possible for a bad cam sensor to cause black smoke. Other possibilities are the MAF and MAP sensors and bad fuel injectors.

Question: Will a bad camshaft position sensor cause a car not to crank over?

Answer: Normally it won't prevent current from reaching the starter, but it may 'disable' the ignition system - no spark.

Question: Would a bad camshaft actuator make a loud noise while driving?

Answer: If the actuator is not being lubricated properly, it'll make a rattling noise when the internal component move from end to end.

Question: What causes a camshaft position sensor to fail multiple times in a 2011 Chrysler Town & Country?

Answer: I believe your model uses a hall type, camshaft sensor. These types are very sensitive to circuit faults (short circuits, voltage surges). Check the circuit wires and connectors for loose or damaged wire that might be causing a problem. Hope this helps.

If necessary, use your repair manual to read and monitor circuit voltage.

Question: Can a faulty cam sensor cause a catalytic converter to get red hot?

Answer: If the faulty cam sensor has a bad effect on ignition timing (at least in some models), it can lead to a misfire; enough raw fuel will cause the catalytic to get red hot.

Question: Would a bad camshaft sensor cause only one cylinder to misfire? The coil plug and injector have all been replaced on my 2004 Jeep Liberty 3.7.

Answer: The computer uses the camshaft sensor to detect cylinder power stroke, using its relative position to the crankshaft. If there's a problem with the signal plate, it's possible to have a misfire in one cylinder. Usually, on these models, the ECM will disable that particular cylinder to prevent raw fuel from going to the cat.

Question: Can a faulty camshaft sensor cause a hard shift in an automatic transmission?

Answer: Yes, a faulty camshaft position sensor can cause hard shifting or lock a gear in place.

Question: When I start on a cold engine everything is fine, but after a minute the engine begins to cough, and there is a malfunction on the camshaft sensor. What could be the issue?

Answer: Check the engine temperature sensor first, and then test the camshaft before changing anything.

Question: What do I do when my car won’t start due to a bad cam sensor?

Answer: Troubleshoot the sensor first to make sure that's the problem - there could be problems with the circuit as well. You may need the vehicle repair manual for this.

Question: Can bad oil cause a cam sensor fail?

Answer: The more like sources of failure is the sensor itself, a problem in the circuit or the PCM.

Question: If the sensor is bad, can the spark be functioning and the injectors not pulse?

Answer: camshaft references compression or exhaust stroke, but a crankshaft position sensor is more likely to affect pulse.

Question: I had the camshaft position sensor replaced for the first time in March. The truck did OK until August. Then it would cut off and hard start, code P0345. I replaced the same sensor in August. Now its November and showing the same symptoms. The car is a 05 Frontier. Also, the SLIP trouble light comes on but goes out when the sensor is replaced. What can cause three sensors to fail in 8 months?

Answer: For some reason, the computer is detecting that the Stability control system is not operating. But the problem might actually be in one of the main systems, and this could be affecting the camshaft position sensor, possibly the sensor’s circuit. Check the connector and related wires. There could be a problem.

Question: What would cause my car to quit while driving? It will only start if you turn off the key and then it starts.

Answer: There could be several causes, restricted fuel filter or problems in the fuel system (check for pressure), bad fuel pump, vacuum leak, or a bad sensor. Check for trouble codes, even if the engine light is not on. There could be a pending code.

Question: What would happen if only one camshaft sensor does not work but the other one works?

Answer: In some models, the engine may still work with one sensor without starting problem if the computer uses the crankshaft signal to figure camshaft position.

Question: What does code P0303 mean related to a camshaft position sensor?

Answer: The computer has detected a cylinder three misfire. This is usually a problem in the ignition system for that cylinder, or sometimes an intake leak affecting that cylinder.

Question: can a faulty Camsensor cause the car to not spark at all?

Answer: Yes, it's possible the ignition system can fail.

Question: What will happen if I confuse the camshaft and crankshaft, thus accidentally trying to start the car with a camshaft sensor where the crankshaft sensor should be?

Answer: I've never done it myself, but both sensors measure speed and position of internal engine components. I would assume within the same application the physical configuration of each sensor is different to avoid mounting the sensor in the wrong place.

Question: What does P0335 code coming from my vehicle mean?

Answer: The P0335 code usually refers to a possible failure of the crankshaft position sensor or the circuit (damage connector or wries). But the fault can also be with the reluctor ring or, less likely, the car computer.

Question: My car has a 345 code. What is that?

Answer: The code points to a problem with the camshaft position sensor - bank 2. A worn voltage reading. Inspect the sensor for contamination, also the wires, or a bad sensor.

Question: I have code PO340 The engine starts and runs fine, "but has extended starter turn over. " Meaning the starter will seem to turn the engine over at least two cycles before it starts. What could be the problem?

Answer: The problem could be with the sensor itself or the circuit. The signal is not properly reaching the computer.

Question: Can a sensor act this bad? I have a Nissan Sentra 2005, and after the car becomes hot; anywhere from 15 minutes to 3 hours, I have to crank it at least twice before it starts. I have replaced the crank sensor, but no change. I replaced the cam sensor four times from different suppliers, and the car won't start hot or cold. So I put the original sensor back in, and it starts. Yet I still have the same issue for that 2 to 3 hours when it's hot

Answer: Some models will not function properly unless you use OEM. Get the DTCs and go from there. You may need to check the circuit as well.

Question: Can a bad CMP cause engine light to come on?

Answer: Yes. Either a circuit or sensor signal problem can throw a P0340 – P0344 trouble code.

Question: What is a Code 0341?

Answer: This usually points to the cam sensor circuit, but it could also be a sensor problem. A loose wire or bad connection (at the sensor or PCM), a bad sensor, or a sensor that has difficulty "reading" the reluctor wheel is possible.

Question: Can a faulty camshaft sensor cause engine to overheat?

Answer: No, but this post might help:

Question: Can a car's camshaft go out if you were hit?

Answer: If it was a hard hit and it caused the sprocket to misalign, it can probably affect the sensor.

Question: Can a faulty camshaft sensor not show a code?

Answer: Usually a camshaft sensor intermittent failure can produce no code. But you'll notice a change in driveability performance at times.

Sometimes it's possible to detect the failure with a scan tool.

Question: My car has lost power and backfires after I shift and surges while driving. What could the problem be?

Answer: It could be a timing issue, but make sure there are no problems in the valve train. Are all the valves working fine? See if you can remove the valve cover and check the valves at idle and see if something doesn't look right. Press the rocker arms with your thumb on each. See if something changes.

Question: My car gets spark and fuel, but still, no start. Can a bad cam sensor cause the no start? I ran a scan which read as a bad sensor.

Answer: On some models, a bad sensor can prevent your car from starting. Check the sensor. Consult your vehicle repair manual for your model for this.

Question: Can a faulty camshaft sensor cause unexpected acceleration while the brake is being applied?

Answer: Besides human error, unintended acceleration usually is caused by a mechanical malfunction in the accelerator assembly (check if something is interfering with the linkage going to the throttle body) -- or from an electrical system malfunction in the cruise control system (sometimes a bad throttle position sensor) or the computer. Haven't heard of a bad camshaft position sensor causing this, though.

Question: How long can I go with a bad camshaft sensor. It happened on 1/25/18. I can only go to 60 miles per hour normal speed and won’t let me go further than that?

Answer: That depends on your particular vehicle make and model. If the sensor actually has failed, you are doing more damage to the engine and you could end up with an expensive repair later on. It's much cheaper to replace it.

Question: I have a P0320 error code, and I replaced both the camshaft and crankshaft sensors. What could be the problem?

Answer: The problem is more likely to be in the circuit, between one of the sensors and the computer (power or ground), a short. Check the connectors (possibly a poor connection) and wiring (loose, damaged or corroded). Less likely, a problem with the computer.

You may need a digital multimeter to check for an incoming reference signal for the sensor(s). This other post can help you check the crank and camshaft sensors. You’ll probably need the wiring diagram to identify the wires and the specs for your model. You can find the diagram in the vehicle repair manual for your model.

Question: I have a 2009 Mini Cooper S that died on the road and will not start. It has the code 2983 Intake Cam sensor and I have replaced it twice. I also replaced the Vanos Solenoid and it still won't start. And the code keeps coming back. Any ideas of what I should do?

Answer: The problem could be in the connector or the wires in the harness. Check the connector for corrosion or buildup, and make sure the wires are not loose. Carefully tug the wires and make sure they are tight and properly connected.

Question: Is repeated failure and replacement of a sensor a symptom of another problem?

Answer: If the same sensor is failing, the problem could be in the circuit. You may want to check the wiring diagram for your particular model. Use your vehicle repair manual. if you don't have the manual, check the reference section of your local library. Possibly you can use a test light or digital multimeter, depending on the circuit you are testing.

Question: Would a faulty cam sensor get worse over time? What are the symptoms over six months?

Answer: On some models you may notice first problems staring the vehicle, then you’ll notice problems while accelerating or at idle (hesitation, stumbling), until the sensor is gone.

Question: I just replaced the camshaft 2 months ago. Why is it bad again?

Answer: Contamination from oil, moister or oil, vibration, can cause a camshaft sensor to fail prematurely. Check the mounting area for signs of contamination and make sure the unit is properly secure. Also, check for wiring damage. This may also cause a bad effect on the sensor itself.

Question: I installed a new distributor 5 months ago and I had a miss immediately. I thought It was maybe a bad plug. Now it either won't start for long periods and shuts off real frequently during idle and while driving. Now I hear it's probably a bad COS and it's located in the distributor as unserviceable part. I don't know how to check it and costly to replace. Could the COS be bad and what is your advice?

Answer: You may need to check the ignition system to trace the fault. Most likely the vehicle repair manual for your model will tell you what tests you can do. If you don't have the manual, check the reference section of your local public library for it.

Question: Can a faulty camshaft sensor make my transmission stop working?

Answer: It is possible in models where sensors share data for the transmission as well. But check the sensor before replacing it.

Question: Can a faulty camshaft sensor stop fuel delivery?

Answer: A faulty sensor may interfere with the ignition and fuel system. The signal is used by the computer to fire the spark and operate the injectors.

Question: Why does the top metal part of my sensor have wear on it like something is scraping it?

Answer: High temperature and vibration may have a "wearing" effect on the sensor's material.

Question: Can a P0335 code be caused by a bad timing chain?

Answer: It's possible, but it's usually more likely to be a fault with a crankshaft position sensor or circuit.

© 2015 Dan Ferrell

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