What a Crankshaft Position Sensor Does and Why It Fails

Your crankshaft position sensor tells your engine's computer where the crankshaft is at every moment. The computer uses this information to time the spark plugs and fuel injectors correctly. When the sensor fails, your engine may not start, may stall while driving, or may run roughly and trigger a check engine light.

The sensor sits near the crankshaft, usually on the front, side, or rear of the engine block depending on your vehicle. It wears out because it lives in heat and vibration. Replacement typically takes 30 minutes to two hours, depending on how straightforward the sensor is to reach on your specific model.

Key Takeaways

  • Locate your crankshaft position sensor by checking your owner's manual or a repair manual for your exact year, make, and model—the location varies widely.
  • You will need a socket set, wrenches, a screwdriver, and possibly a sensor socket or removal tool, depending on how the sensor is mounted.
  • Disconnect the negative battery terminal before you start work to prevent electrical damage to the computer.
  • The sensor usually bolts or screws in place; remove the fastener, unplug the electrical connector, and pull the sensor straight out.
  • Install the new sensor in reverse order, torque the fastener to your manual's specification (usually 15 to 25 foot-pounds), and reconnect the battery.

Gather Your Tools and Parts

Before you start, collect the correct replacement sensor for your vehicle. Use your vehicle identification number (VIN) or your owner's manual to order the exact part. Buying the wrong sensor wastes time and money.

You will need basic hand tools: a socket set with ratchet, open-end wrenches, a screwdriver (Phillips and flathead), and possibly a sensor socket if the sensor is recessed. Some vehicles require a special removal tool—your repair manual will tell you. Have a drain pan nearby in case any coolant spills, and wear safety glasses. Disconnect the negative battery terminal first by loosening the nut on the cable clamp with a wrench and sliding the cable off the post.

Locate the Sensor on Your Engine

The crankshaft position sensor location depends entirely on your vehicle's design. On some cars it sits near the front of the engine block, on others near the rear, and on some along the side. Your owner's manual has a diagram showing exactly where it is. If you do not have the manual, a repair manual for your year, make, and model (available in print or online) will show you the location and the steps specific to your engine.

Once you find it, you will see an electrical connector plugged into the sensor and a bolt or screw holding it in place. Take a photo with your phone before you disconnect anything—it helps you remember the exact angle and position when you install the new one.

Remove the Old Sensor

Unplug the electrical connector by pressing the release tab or clip (usually on the side of the connector) and pulling straight back. Do not yank on the wires themselves. Set the connector aside where it will not get dirty or damaged.

Remove the bolt or screw holding the sensor in place using the correct socket or wrench. The fastener is usually small—typically 8 to 10 millimeters. Keep the bolt in a safe place so you do not lose it. Gently pull the sensor straight out of its hole. If it is stuck, wiggle it slightly side to side while pulling, but do not force it or you may break the mounting hole. Some sensors have an O-ring seal; if it stays in the hole, remove it by hand or with a small pick.

Install the New Sensor

Before you insert the new sensor, check whether it has an O-ring or rubber seal. If the old sensor left a seal in the hole, clean it out. If your new sensor comes with a fresh O-ring, make sure it is seated properly on the sensor body. A misaligned O-ring can cause an oil leak or a poor electrical connection.

Insert the new sensor into the hole at the same angle as the old one (your photo helps here). Push it in until it seats fully. Install the bolt or screw and tighten it to the torque specification in your repair manual—usually between 15 and 25 foot-pounds. Do not overtighten; you can crack the sensor or strip the threads. Plug the electrical connector back in until you hear or feel it click.

Reconnect the Battery and Clear the Check Engine Light

Reconnect the negative battery terminal by sliding the cable clamp onto the post and tightening the nut with a wrench. Start the engine and listen for any unusual sounds. The check engine light may stay on for a few driving cycles while the computer relearns the sensor signal. If the light does not go off after 50 to 100 miles of normal driving, the sensor may be defective or you may have installed it incorrectly.

If you have a code reader, you can clear the old fault code yourself by connecting the reader to the diagnostic port under the steering wheel and following the reader's menu. Many auto parts stores will clear the code for you at no charge. Do not ignore a persistent check engine light—it means the computer is not receiving the correct signal from the sensor.

Common Mistakes to Avoid

The most common error is installing the sensor at the wrong angle. The sensor must point at the reluctor ring or trigger wheel on the crankshaft. If it is tilted or rotated, the computer will not read it correctly and the engine will not run properly. Your photo and your repair manual prevent this mistake.

Another mistake is forgetting to disconnect the battery before you start. This can damage the engine computer if you accidentally short a wire. Overtightening the sensor fastener can crack the sensor body or strip the threads in the mounting hole, requiring a costly repair. Use a torque wrench if you have one, or tighten firmly but not with all your strength.

Do not reuse the old O-ring or seal. Always install the new one that comes with the sensor or purchase a replacement seal. A leaking seal allows oil to enter the sensor connector and causes electrical failure.

Frequently Asked Questions

How do I know if my crankshaft position sensor is actually bad?

A failing sensor usually triggers a check engine light with a code like P0335 or P0336. You can read the code with a code reader (available at auto parts stores or online). Other signs include the engine not starting, stalling while driving, rough idle, or hesitation during acceleration. Have the code read before you assume the sensor is the problem—other issues can cause similar symptoms.

Can I drive with a bad crankshaft position sensor?

Not safely. Without a correct signal from the sensor, the computer cannot time the spark plugs or fuel injectors. The engine may not start at all, or it may stall without warning while you are driving. Do not drive the vehicle until the sensor is replaced.

Do I need to reset the computer after I install a new sensor?

No. The computer will relearn the new sensor signal automatically as you drive. The check engine light may stay on for a few driving cycles. If it does not go off after 50 to 100 miles, the sensor may be installed incorrectly or may be defective.

What if the sensor is stuck and I cannot remove it?

explore penetrating oil (like WD-40 or PB Blaster) around the sensor body and let it soak for 15 to 30 minutes. Gently wiggle the sensor side to side while pulling. If it is still stuck, tap the wrench or socket lightly with a hammer to help break the corrosion. Do not force it hard enough to break the sensor or damage the hole.

How much does a crankshaft position sensor cost?

The sensor itself usually costs between $40 and $150 depending on your vehicle. Labor at a shop typically adds $100 to $300. Doing the work yourself saves the labor cost if you have the tools and feel confident following your repair manual.