What a crankshaft position sensor does and why it fails

Your crankshaft position sensor tells your engine computer where the crankshaft is at any given moment. The computer uses that signal to time the spark plugs and fuel injectors. When the sensor fails, the engine either won't start, runs rough, stalls randomly, or triggers a check engine light. The sensor itself is a small cylindrical part that sits near the crankshaft, usually held in place by one bolt.

These sensors fail because they live in a hot, oily environment and wear out over time—typically between 80,000 and 200,000 miles depending on the sensor type and your vehicle. You'll know it's failing if your car won't start, hesitates under acceleration, or the check engine light comes on with a code like P0335 or P0336.

Key Takeaways

  • The crankshaft position sensor bolts to the engine block near the crankshaft and takes 15 to 45 minutes to replace on most vehicles.
  • You will need a socket set, a wrench, possibly a sensor socket, and the correct replacement sensor for your make, model, and year.
  • The hardest part is locating the sensor—it can be tucked under the intake manifold, behind the engine, or near the oil pan, so check your repair manual first.
  • Disconnect the negative battery terminal before you start work to avoid triggering airbags or damaging the computer.
  • If the sensor is seized or you cannot reach it safely, call a mechanic rather than forcing it or working in an unsafe position.

Locate the sensor and gather your tools

Before you buy a replacement sensor, you need to know where yours sits. The location varies wildly by engine design. On some vehicles it's bolted to the front of the block near the crankshaft pulley. On others it's mounted on the back of the engine, tucked under the intake manifold, or wedged near the oil pan. Your repair manual or a parts diagram for your specific year, make, and model will show you the exact spot.

Once you know where it is, gather your tools: a socket set, an adjustable wrench or open-end wrench in the size that fits the sensor bolt (usually 10 mm or 13 mm), a screwdriver, and possibly a sensor socket if the sensor is recessed and hard to reach with a regular socket. Buy the correct replacement sensor before you start—they are not interchangeable between models. Write down your vehicle's year, make, model, and engine size when you order it.

Disconnect the battery and remove the old sensor

Open your hood and locate the negative battery terminal—it's the black cable on the battery. Loosen the nut on the terminal with a wrench and slide the cable off. This step prevents accidental electrical damage and stops the airbag system from deploying if you bump something while working.

Now locate the sensor's electrical connector. It's a plastic plug with two or three wires running into it. Squeeze or pry the connector clip gently and pull the connector straight out. If it's stuck, wiggle it side to side as you pull—do not yank on the wires themselves.

Unbolt the sensor. Use your socket and wrench to turn the bolt counterclockwise. The bolt usually comes out easily, but if it's seized or corroded, spray it with penetrating oil and wait 10 to 15 minutes before trying again. Once the bolt is loose, unscrew it by hand and set it aside. Slide the sensor out of its mounting hole.

Install the new sensor and reconnect everything

Before you install the new sensor, check that the mounting hole is clean and free of oil, dirt, or debris. Wipe it out with a clean rag if needed. Slide the new sensor into the hole and hand-thread the bolt to hold it in place. Tighten the bolt with your socket and wrench—snug it firmly but do not overtighten, which can crack the sensor body. Most sensors need only 15 to 25 foot-pounds of torque; if you have a torque wrench, use it.

Reconnect the electrical connector by pushing it straight onto the sensor plug until you hear or feel a click. Reconnect the negative battery terminal by sliding the cable back onto the post and tightening the nut with a wrench.

Start the engine and clear the check engine light

Turn the ignition key to the "on" position without starting the engine. Wait a few seconds, then turn it back to "off." This allows the computer to recognize the new sensor. Now start the engine. It should start normally and run smoothly. If the check engine light is still on, the computer may need a few drive cycles to clear it on its own—drive the vehicle normally for 50 to 100 miles and the light should go out.

If the light stays on or the engine still runs rough, the problem may not have been the sensor, or the new sensor may be faulty. In that case, have a mechanic read the diagnostic code to confirm the sensor is working correctly.

When to call a mechanic instead

If the sensor bolt is severely corroded and won't budge even after soaking with penetrating oil, stop and call a mechanic. Forcing a stuck bolt can snap it off inside the hole, which turns a straightforward job into an expensive one. The same applies if the sensor is mounted in a spot that requires removing other engine components to reach it safely—some vehicles require you to remove the intake manifold or oil pan, which is beyond a basic DIY job.

Also call a mechanic if you are not comfortable working under the hood, if you lack the tools, or if you are unsure about the location of your sensor. A professional can do the job in under an hour and will warranty the work.

Frequently Asked Questions

How much does a crankshaft position sensor cost?

The sensor itself typically costs between $40 and $150 depending on your vehicle's make and model. OEM (original equipment manufacturer) sensors are usually more expensive than aftermarket ones. Labor at a shop runs $100 to $300 depending on how hard the sensor is to reach.

Can I drive with a bad crankshaft position sensor?

No. A failed sensor will prevent the engine from starting or cause it to stall while driving. If the sensor is failing gradually, you may notice rough idling or hesitation, but you should not rely on the vehicle to run reliably. Have it replaced as soon as you can.

Will replacing the sensor clear the check engine light?

The light should go out after a few drive cycles once the new sensor is installed and working. If it stays on, the computer may have stored a different fault code, or the new sensor may be defective. A mechanic can read the code to find out what's wrong.

Do I need a special tool to remove the sensor?

Most sensors come out with a standard socket and wrench. Some sensors sit in a recessed hole and need a sensor socket—a deep socket with a slot cut in the side so the electrical connector can pass through. Ask the parts store whether your sensor needs one when you buy the replacement.

What if the sensor is stuck and won't come out?

Spray the bolt with penetrating oil and let it soak for 15 to 30 minutes. Try again gently. If it still won't budge, stop and call a mechanic. Forcing a stuck bolt risks breaking it off inside the engine block, which is a much bigger repair.