Symptoms of a Bad Crankshaft Position Sensor

Your car has many different sensors on board, one of which is the crankshaft position sensor (CKP). Like any other car part, the crankshaft position sensor can eventually fail, and when it does, it can cause a variety of problems.

A replacement can cost as little as a few dollars for a few models, but it’s more common to pay between $40 and $150 for the part. Learn what symptoms it presents, how to diagnose it, and what can occur if you ignore it.

What Does a Crankshaft Position Sensor Do?

The crankshaft is a rotating assembly inside the engine that connects to the pistons and connecting rods. When the engine is running, the linear motion of the pistons causes the crankshaft to turn, thereby creating the rotational force needed to move the vehicle.

As you might guess, the CKP sensor measures the position and speed of the engine’s crankshaft. The sensor creates a signal by reading a toothed or notched wheel that is usually located on the crankshaft or harmonic balancer.

For this reason, the crankshaft position sensor’s location is often at the front bottom side of the engine, though, its location can vary from vehicle to vehicle.

The engine computer, which is often referred to as the powertrain control module (PCM), uses the CKP sensor signal when calculating spark timing and (in most cases) fuel injector synchronization.

The PCM may also use the CKP signal when managing other functions, such as the variable valve timing system if the vehicle is so equipped. On all vehicles built after 1996, the module also uses the CKP sensor to detect an engine misfire. 

Bad Crankshaft Position Sensor Symptoms

As the crankshaft position sensor goes bad, it gives one of the below-given signs:

• 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 the first sign of a faulty crankshaft position sensor.

The powertrain control module (PCM) continuously communicates with the crankshaft position sensor to control different features of the engine. When the sensor goes bad, it sends inaccurate data about the crankshaft’s speed and position to the PCM.

When the PCM receives wrong information from the CKP sensor, it triggers the check engine warning light on the dashboard to alert the driver. Your PCM may also trigger the trouble codes P0335 or P0336 along with the check engine light.

#2. Excessive Engine Vibrations.

An engine with a malfunctioning crankshaft position sensor doesn’t operate at peak performance. The powertrain control module (PCM) of the vehicle uses the data of the crank sensor to regulate the ignition timing and many other features.

If your PCM uses incorrect readings from the crankshaft sensor to determine fuel and ignition timing, it may lead to a bumpy driving experience.

If the PCM fails to time these processes correctly for a long time, the issue will only worsen until it is resolved, potentially causing further damage.

#3. Hard Starting.

When a faulty crankshaft position sensor is severely out of sync, you may struggle to start your car or keep it running. This issue typically arises when the problem has persisted for a long time, potentially indicating other underlying issues.

However, if your check engine light is on and the PCM has defaulted to predetermined values, this might not be an immediate concern.

Instead, this issue usually arises when the crankshaft position sensor provides inaccurate readings, and the PCM fails to detect it.

#4. Poor Engine Performance.

As we discussed above, engine performance highly depends on the performance of the crankshaft sensor. Poor engine performance is one of the clear symptoms of a faulty crankshaft position sensor.

When this sensor goes bad, it significantly impacts the PCM’s ability to maintain proper fuel injection rate and ignition timing.

As a result, you may experience a hesitation when pressing the gas pedal harder, or the engine might not respond at all. This may be particularly hazardous on roads where quick acceleration is necessary.

#5. Engine Misfire.

A faulty crankshaft position sensor may also cause misfiring. This issue occurs when a faulty crank sensor sends wrong information about the piston position to the PCM, which in turn results leads to misfires within one or more of the combustion chambers.

However, your car may misfire due to many other issues. However, a bad spark plug can also cause this issue. Therefore, it is important not to dismiss the possibility of a faulty crankshaft position sensor if you’re experiencing other related symptoms.

#6. Poor Fuel Economy.

As we discussed above, the main function of the crankshaft position sensor is to measure the crankshaft position and send this data to the PCM. The PCM utilizes this data to adjust fuel injection rate, and ignition timing, ensuring optimal engine performance and efficiency.

When the crankshaft sensor becomes faulty, it starts sending wrong information to PCM. When the PCM receives wrong information, it may be unable to efficiently regulate the fuel injection rate, resulting in a lean or rich air-fuel mixture.

The poor air-fuel mixture leads to poor combustion and your engine works hard to properly combust the mixture. As a result, your engine starts to consume more fuel than normal.

#7. Engine Stalling.

Frequent engine stalling can occur when driving with a bad crankshaft position sensor. If this issue is left unaddressed, your engine may eventually stop functioning altogether.

Your vehicle engine may stall due to many other reasons, such as a faulty fuel injector or faulty camshaft sensor. Therefore, when your engine stalls, properly inspect all the parts to find the root cause of the engine.

#8. Car Jerking.

A faulty crankshaft position sensor may lead to the car jerking while driving. When the sensor goes bad, the PCM will be unable to properly control the ignition timing and fuel injection.

This leads to hesitation or sudden variations in engine speed, which may cause the vehicle to jerk.

#9. Rough Idle.

A faulty crankshaft sensor may lead to a rough idle. The crankshaft position sensor is one of the major components of the engine management system.

When it becomes faulty, it may lead to poor combustion of the air-fuel mixture in the combustion chamber, which causes a rough idle.

What Causes A Crankshaft Sensor To Go Bad?

There are several factors that can cause a crankshaft sensor to fail. 

In crankshaft sensors that contain magnets, a build-up of dirt on the magnet can block the sensor and prevent it from seeing the engine’s spin.

Another factor in the lifespan of a crankshaft sensor is its age – the magnet in the sensor loses its pull over time, which means it grows less capable of providing accurate signals to the ECU. Faulty, lose or damaged wiring can affect the sensor’s ability to send signals accurately to the ECU. 

The crankshaft sensor is a clever piece of kit, but it can be fooled. If the gear which the sensor is tasked with observing suffers damage, the sensor can’t be sure of what it’s looking at, which can cause confusion as it sends mixed signals to the ECU. This will likely bring up an engine check light.

There’s also the chance the sensor is damaged by a hit from another component inside the engine such as the crankshaft pickup, or by road debris.

If that component is repaired but the engine is still having difficulty starting, the unnoticed damage to the sensor could be what’s causing it.

How To Tell If Your Crankshaft Is Faulty

If your engine refuses to start and your ignition continues to click over without any success, you may be able to blame it on a faulty crankshaft position sensor.

Without it, your engine will have trouble knowing when to fire the spark plugs or even inject fuel, so good luck getting things started!

How to Test a Crankshaft Position Sensor

If you’re able to locate your crankshaft position sensor under your hood, commonly found either in the front or the back of the crankshaft on a bell housing or tucked behind something, you can complete the following test to determine if your engine not starting can be blamed on your sensor:

• Inspect the sensor: Look for signs of damage to the housing, as it can commonly get burnt or covered in dirt, oil, or other debris and stop working correctly.
• Use a multimeter: If you have a multimeter on hand, pull it out, put it on the ohms setting, and take the sensor’s measurement.
• Read the results: The meter should read a resistance value anywhere from 200 to 1,000 ohms (or more depending on the model). If it has 0 ohms, it will need to be replaced.

How to Replace Your Crankshaft Position Sensor

You can replace your own crankshaft position sensor to save yourself $100 or more on the labor cost of having a mechanic do it. This sort of thing requires a modest amount of mechanical skill and a somewhat extensive automotive tool kit.

Once you’ve found it, you can replace your failing crankshaft position sensor using the following steps.

• Step One: Disconnect the negative terminal of the car’s battery.
• Step Two: Access the crankshaft position sensor and carefully remove any non-essential components that might be in the way, such as the timing cover. If your car’s crankshaft position sensor is mounted at the front of the engine, you might also need to remove the serpentine belt along with the crankshaft pulley. If the bad crankshaft position sensor is mounted near the transmission, you might have to remove the starter motor.
• Step Three: Note the three wires coming out of the crankshaft position sensor. Take a picture with your phone or label them in a side drawing. They are the input, output, and the ground wire. Carefully set them aside without letting them touch anything wet or metallic.
• Step Four: Remove the two small bolts holding the sensor in place.
• Step Five: Compare the bad crankshaft position sensor to the new one to ensure they match.
• Step Six: Reconnect the three wires to the sensor in the same ports that you removed from the bad crankshaft position sensor. If they are not in the correct ports, the sensor will fail to work, and you’ll return to square one!
• Step Seven: Reconnect the mounting bolts holding the new crankshaft position sensor in place. Then, reinstall all the other components you removed in reverse order. Finishing with reconnecting the car’s battery.
• Step Eight: Clear all the codes and start the car. Check to see how it idles. Rev the engine a little to see if the symptoms of a bad crankshaft sensor return.

If the car seems to operate normally, you can take it out for a 15 to 20-minute test drive. Ideally, you want to tool around town roads and residential streets to make sure there aren’t any stalling, misfiring, or surging acceleration issues.

Then, you can take it out to the highway to see how it handles accelerating, like merging and passing at high speed.

Crankshaft Position Sensor Replacement Cost

The cost of crankshaft position sensor replacement often differs from one vehicle to the next, due to variances in parts costs and labor attributed to such a repair. Those that are mechanically savvy, and own their own set of basic hand tools can often complete such repairs on their own, saving themselves money along the way.

When having a vehicle’s crankshaft position sensor professionally replaced, you can expect to pay between $175-$300.

By contrast, the cost of the sensor itself typically tallies up to $45-$85, thus illustrating the amount of savings that can be had from tackling this repair from a DIY standpoint.

Common Causes of Failure

A vehicle’s crankshaft position sensor can fail for one of several different reasons, some of which tend to be more common than others.

Perhaps the most common culprit of failure is damage to the crankshaft position sensor’s circuitry. It’s not uncommon for sensors of this type to fail at their plugs, failing to provide reliable continuity. Alternatively, a crank position sensor can fail internally, or its wiring harness/pigtail can become pinched or chafed.

It’s also not uncommon for crankshaft position sensors to become damaged during undercarriage debris strikes. Due to the proximity of this sensor to the lower half of a vehicle’s engine, tire casings, and other road litter make formidable opponents to the crank position sensor when struck while in the lane of travel. 

Age and heat also serve as mortal enemies to a vehicle’s crankshaft position sensor. With time, the actual structural body of the crankshaft position sensor can become brittle, making it subject to failure under vibration. Unfortunately, there is little that can be done to prevent this from occurring.

Diagnosing a Faulty Sensor

One of the simplest ways to diagnose a faulty crankshaft position sensor involves the use of a multimeter. Resistance can be checked across this sensor, and compared to resistance readings specified by the vehicle’s manufacturer.

Infinite resistance across the sensor’s terminals would indicate an “open” condition, while a lack of recordable resistance would indicate a “shorted” condition. Output of the crankshaft position sensor can also commonly 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 validate crankshaft position sensor feedback. Live data reporting via a scan tool should show a rise/fall in pulse counts that parallel any rises or falls in engine RPM.

A lack of this feedback would require further diagnosis of the crankshaft position sensor and its corresponding circuit.

Can You Drive With a Bad Crankshaft Position Sensor?

Attempting to knowingly drive with a faulty crankshaft position sensor is never advised, due to a high risk of encountering driveability-related issues.

While it is true that some engines will continue to run despite a faulty crankshaft sensor, others will not, and even those that do, are not guaranteed to continue doing so indefinitely.

Modern computer-monitored engines rely upon accurate engine timing-related feedback to facilitate efficient and properly timed combustion. Without an uninterrupted stream of such data, a vehicle’s engine is likely to run erratically at best.

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

With this in mind, issues pertaining to a vehicle’s crankshaft position sensor should always be diagnosed and repaired as soon as possible. Doing so can quite possibly prevent you from becoming stranded roadside, and will go a long way to eliminating any uncertainties.

If you lack the confidence or expertise to handle this repair on your own, it’s recommended to schedule an appointment with a reputable automotive service center as soon as possible.

FAQs.