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. 

Symptoms Of A Bad Crankshaft Position Sensor

Recognizing the signs of a faulty crankshaft position sensor can prevent further damage and costly repairs. Here are some common symptoms:

#1. Trouble Starting The Engine.

The crankshaft sensor is responsible for keeping a close eye on the position and speed of the crankshaft when starting the engine. So if it’s unable to relay information back to the ECU, the engine may not start.

If the engine is currently running, you may not even notice an issue here regardless of whether or not there’s an engine light – the sensor uses an algorithm to estimate where the crank has spun to based on previous knowledge, so the engine won’t shut off due to electronic override.

It’s only when you key off the engine and try to restart the vehicle later that an issue will occur.

#2. Intermittent Stalling.

When the crankshaft position sensor is on the fritz, it may produce a weak or erratic signal rather than failing completely. As a result, the vehicle may exhibit hard starting and/or stalling due to improper spark and fuel delivery.

#3. Check Engine Light Is On.

If the sensor isn’t relaying information to the ECU, or what it is sending appears troubling, the ECU will respond by turning on the engine light – your cue to assess what’s ailing the vehicle.

The engine light could be caused by a range of different issues aside from the crankshaft sensor. A diagnostic tool can help you to identify if the sensor is the part that’s causing concern.

#4. Poor Acceleration.

If your vehicle doesn’t accelerate smoothly or as quickly as usual, the sensor might be to blame.

#5. Fuel Efficiency Concerns.

 The faulty crankshaft position sensor that lacks accurate timing information may cause fuel injectors won’t pump fuel into the engine efficiently, and the vehicle will lose power and consume more fuel. If you notice that the car consumes more fuel when you drive at the same distance, it’s a sign of a bad crankshaft position sensor.

When the crankshaft position sensor is working erratically, these symptoms can come and go seemingly randomly. It can make it tricky to figure out what’s at the heart of the issue.

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.

FAQs.