Symptoms of a Bad Crankshaft Position Sensor

Your car contains a large variety of sensors on board, and one of these is called the crankshaft position sensor, or CKP for short. Like any car part, the crankshaft position sensor can fail like anything else, and when it does fail, it can cause various problems.

It can be replaced for anywhere from a few dollars for some models, to a more common price range of $40-$150. This article will explain what symptoms the crankshaft position sensor may create, how to diagnose it, and what could happen if you allow it to go ignored.

What Does a Crankshaft Position Sensor Do?

The crankshaft is the rotating assembly that is inside the engine that connects the crankshaft connecting rods and pistons. When the engine is running, the crankshaft spins as the pistons move in a linear motion, thus creating the rotational force that is required to propel the vehicle.

As you may guess, the CKP sensor monitors the engine’s crankshaft speed and position. The sensor generates a signal, through a toothed or notched wheel that is usually on the crankshaft or harmonic balancer.

Therefore, the crankshaft position sensor is often located at the front bottom of the engine, although again, it may differ from vehicle to vehicle.

The engine computer, often called the powertrain control module (PCM) uses the CKP sensor signal when computing spark timing and (for most vehicles) fuel injector synchronization.

In addition to spark timing and fuel injector synchronization, the PCM uses the CKP sensor signal when controlling other functions, like the variable valve timing system (if applicable). For all vehicles made from 1996 onward, the PCM uses the CKP sensor to determine whether the engine has misfired. 

Bad Crankshaft Position Sensor Symptoms

If the crankshaft position sensor is failing, it will show one of the following symptoms:

• Illuminated check engine light
• Excessive engine vibrations
• Hard starting
• Poor engine performance
• Engine misfire
• Poor fuel economy
• Engine stalling
• Car jerking
• Rough idle

#1. Illuminated Check Engine Light.

The illuminated check engine light is a very obvious first indication of a faulty crankshaft position sensor.

The powertrain control module (PCM) is in continuous communication with the crankshaft position sensor for several engine functions. When the crankshaft position sensor is faulty, it will relay false information about the crankshaft speed and angular position to the PCM.

When the PCM receives bad information from the CKP sensor, it will turn on the check engine light to tell the user something is wrong. Your PCM may also set the trouble code P0335 or P0336 along with the check engine light as well.

#2. Excessive Engine Vibration.

When the crankshaft position sensor is faulty, the engine will not perform optimally. The vehicle’s powertrain control module (PCM) relies on the crank sensor data to manage the ignition timing of the engine and many other features.

If your PCM receives wrong information from the crankshaft sensor about fuel and ignition timing, you will likely experience a vehicle that shakes, rattles, and rolls.

The longer your PCM uses the wrong timing, the bigger issue you will create until the problem is resolved, and the more significant damage may occur as well.

#3. Hard Starting.

When the crankshaft position sensor is faulty, and is way out of sync, you may have trouble starting your car or keeping it running. This situation usually occurs after the crank position sensor problem has existed for some time. This can be a clue to other problems.

If your check engine light is on, and your PCM has gone back to its default predetermined values, this is not much of a concern.

This situation usually arises when the crankshaft position sensor is providing wrong readings to the PCM, and the PCM is simply unable to recognize it.

#4. Poor Engine Performance.

As noted above, engine performance relies heavily on the crankshaft sensor. Poor engine performance is a clear symptom of a faulty crankshaft position sensor.

When this sensor fails it greatly affects what the PCM will be able to do properly in sustaining the proper fuel injection rate and ignition timing.

So, you may experience hesitation when you press the gas pedal harder, or there may be no response from the vehicle’s engine. This failure can be dangerous when you need to accelerate out on the road and need a quick response.

#5. Engine Misfire.

Another indicator of a faulty crankshaft position sensor is misfire. A misfire occurs when a faulty crank sensor informs the powertrain control module, (PCM) that a piston position is in a different location, causing whole number of missed firings in one or more of the combustion chambers.

However, misfire can also stem from many other issues. Misfire occurs because of a bad spark plug, etc, but this is not intended to eliminate a crankshaft position sensor from your list of possible causes when considering other related symptoms.

#6. Poor Fuel Economy.

As stated above, the main purpose of the crankshaft position sensor is to measure crankshaft position and communicate this data with the PCM. The PCM uses this data to regulate ignition timing and fuel injection rate for best performance and fuel efficiency.

When the crankshaft sensor is not operating correctly, it starts sending wthe rong data to the PCM. When the PCM has wrong data, it might not be able to efficiently regulate the fuel injection rate, as it may sense a lean or rich air-fuel ratio.

As a result of the poor air-fuel ratio, there is poor combustion and the engine will have to work hard to properly combust the air-fuel mixture. The engine will end up using more fuel than it normally would.

#7. Stalling Engine.

Operating a vehicle with a bad crankshaft position sensor, it will cause constant or frequent stalling. If you persist with this problem, the engine will stop working completely.

There are many more reasons as to why your vehicle engine may stall, such as a faulty fuel injector, bad camshaft sensor, or other possible components. Therefore, if your engine is stalling, inspect all the components to ensure you have the correct root cause for the engine stalling.

#8. Jerking vehicle.

A faulty crankshaft position sensor may also cause your vehicle to jerk while driving. A faulty crankshaft position sensor will no longer allow the PCM to properly control ignition timing and fuel injection from the crankshaft position.

This may result in hesitation or sudden changes in speed from the engine, which may cause the car to jerk.

#9. Rough Idle.

A faulty crankshaft sensor may also cause rough idling. The crankshaft position sensor is vital to the engine management system. 

When it fails, it will cause rough combustion of the air-fuel mixture, resulting in a rough idle.

What Caused A Crankshaft Sensor To Fail?

There are a number of reasons that can cause a crankshaft sensor to fail

For crankshaft sensors that contain magnets, often dirt can build up on the magnet, which can obstruct the sensor and prevent it from seeing the spin of the engine.

Another factor of the life cycle of a crankshaft sensor is the age of the sensor, as the magnet itself will lose its pull and become less able to provide accurate signals to the ECU. Worn, loose or damaged wires can influence the sensor’s ability to provide accurate signals to the ECU.

While a crankshaft sensor is quite clever, there are ways it can be tricked. If the gear that the sensor is observing suffers damage then the sensor can’t be sure of what it is observing which leads to confusion in sending signals to the ECU. This will bring up an engine check light.

It is also possible the sensor was damaged through travel by the crankshaft pickup, or even by road debris. If the component is repaired but the engine is still having difficult starting, that unnoticed damage to the sensor could be the culprit.

How To Know If Your Crankshaft Is Bad

If you have a no-start problem, and the ignition is just clicking over but your engine refuses to fire, you may have a bad crankshaft position sensor.

With no crankshaft position sensor the engine will not know when to fire the spark plugs or even inject fuel! So don’t plan on starting it any time soon!

How To Check the Crankshaft Position Sensor

If you can find your crankshaft position sensor under your hood, the most common spot is either on the front or back of the crankshaft on a bell housing, or behind something. You can try to test it to see if you can blame your no-start on this sensor:

• Check it visually: Look for a damaged housing as it may have been burnt, or it probably has dirt/oil/debris and has stopped working properly.
• Check it with a multimeter: If you have a multimeter handy, pull it out, set it to ohms, and read the measurement on the crankshaft position sensor.
• Interpret your readings: The meter will read a resistance value of anything between 200 and 1,000 ohms (or more-depending on the model). If it reads 0 ohms, it needs to be replaced.

How to Replace Your Crankshaft Position Sensor

You can tackle replacing your own crankshaft position sensor and save yourself $100 or more, which is the labor time to have a shop do it. You should have decent mechanical skills and an adequate automotive tool kit.

Once you have identified the crankshaft position sensor, you can go through the steps below to replace a failing crankshaft position sensor.

• Step One – Disconnect the negative terminal on the vehicle’s battery.
• Step Two – You will need to gain access to the crankshaft position sensor. Some ancillary items that may or may not need removing will be: the timing cover; the serpentine belt and the crankshaft pulley (most of the time it is at the front of the engine); the starter motor (if near the transmission).
• Step Three – Remember the 3 wires attached to the crankshaft position sensor? Take a picture of them with your phone or label them in a side drawing. They are an input, output, and ground wire. Carefully set them aside without letting them make contact with any wet or metallic parts.
• Step Four – Remove the 2 small bolts to release the crankshaft position sensor from the engine.
• Step Five – Compare the failed crankshaft position sensor and the new one to ensure they match.
• Step Six – Reattach the 3 wires to the sensor in the same ports (this is critical). If you do not connect to the port correctly, the new sensor will not work, and you will be exactly back to where you started!
• Step Seven – Reattach the new crankshaft position sensor by connecting the original bolts that held the original sensor to the engine. Reattach everything that was removed in reverse order to the disassembly process. Finally, reconnect the vehicle’s battery.
• Step Eight – Clear all the codes, and start the vehicle. Determine how the vehicle is idling & rev the engine a little, and see if you can duplicate the symptoms of a bad crankshaft position sensor.

If the vehicle seems to operate normally, take the vehicle for a 15–20-minute test drive. You ideally want to drive on the town roads and residential streets, to ensure that there are no stalling, misfiring, or surging acceleration troubles.

Then you can take it to the highway to see how it accelerates when merging and passing at high speed.

Cost of Crankshaft Position Sensor Replacement

The cost of replacing a crankshaft position sensor is usually specific to the vehicle, but can range considerably due to the cost of parts and labor involved. If someone is mechanically inclined and owns their own basic set of hand tools, they may be able to do this work themselves and save some money.

If you need a crankshaft position sensor replaced by a mechanic, you can expect to pay anywhere from $175 to $300.

The cost of the sensor Themselves range from $45-$85 and illustrates the potential savings achieved by doing this repair yourself.

Common Causes of Crankshaft Position Sensor Failure

There are several different ways that a crankshaft position sensor can fail or various reasons why it may be damaged, with some being more common than others.

The most common reason for the failure of a crankshaft position sensor is damage to the circuitry, which is generally in the form of actual damage to the sensor’s plugs, or causing the sensor to lose continuity. Crankshaft position sensors can fail internally or due to a pinched or chafed wiring harness or pigtail.

It’s also not uncommon, for crankshaft position sensors to be damaged from debris when it gets struck from the undercarriage.

Due to the fact that the crank position sensor is located relative to the lower half of a vehicle’s engine, tire casings, and other rubbish on the road become serious adversaries to the crank position sensor when they strike the crank position sensor while in the lane of travel.

Age and heat are also deadly foes of a vehicle’s crankshaft position sensor. Given enough time, the actual crankshaft position sensor ‘body’ can become brittle making it susceptible to failure under vibration. Unfortunately, there is not much that can be done to prevent this from happening.

Diagnosing A Failing Sensor

One of the easiest ways of diagnosing a failing crankshaft position sensor is with a multimeter. The resistance should be checked across this sensor, and then compared to resistance readings provided by the vehicle manufacturer.

Infinite resistance across the terminals of the sensor would indicate an “open” condition, while nil recordable resistance would indicate a “shorted” condition. Output of the crankshaft position sensor can also usually be verified while cranking a vehicle’s engine, in the form of AC millivolts. 

Alternatively, a quality OBD-II scan tool can also be used to verify crankshaft position sensor feedback. The live data reporting via the scan tool should provide either a rise/fall in pulse counts that mirror associated rises or falls in engine RPM.

If there is no associated feedback, further diagnosing of the crankshaft position sensor, and the circuit, would be justified.

Can I Drive with A Bad Crankshaft Position Sensor?

Driving with a known faulty crankshaft position sensor is never advisable due to the risk of experiencing drivability issues.

Some engines will indeed run with a faulty crank sensor, but others will not, and even ones that do will not necessarily do so reliably.

Modern computer-controlled engines depend on accurate feedback related to engine timing data to operate combustion efficiently and consistently. Thus, if there is not a constant stream of data, a vehicle’s engine may run erratically at best.

In some instances, an engine can stall and refuse to restart if the signal from the crankshaft position sensor is interrupted. 

For these reasons, crankshaft position sensor related vehicle issues should always be diagnosed and repaired immediately. Doing so can potentially save you from being stranded on the side of the road, and will hopefully remove any doubt.

If you do not feel comfortable, or competent to make this repair on your own, than an appointment should be scheduled with a reputable automotive service center at your earliest convenience.

FAQs.