What a crankshaft position sensor does and why it fails

A crankshaft position sensor tells your engine computer where the crankshaft is at any given moment. The computer uses this information to time the spark plugs and fuel injectors correctly. When the sensor fails, the engine often won't start, runs rough, stalls without warning, or triggers 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 reads a toothed ring on the crankshaft as it spins. Over time, the sensor's internal electronics wear out, or the connector corrodes. Replacement is straightforward on most vehicles and takes between 30 minutes and two hours.

Key Takeaways

  • The crankshaft position sensor bolts to the engine block near the crankshaft and costs between $50 and $250 for the part itself.
  • You will need basic hand tools, a socket set, and possibly a sensor socket or removal tool, depending on how tight the old sensor sits.
  • The sensor location varies by vehicle make and model, so check your owner's manual or a repair guide specific to your car before you start.
  • After installation, the check engine light may stay on until you clear the code with a scanner or drive the vehicle through a full startup cycle.

Locate the sensor on your specific vehicle

The crankshaft position sensor location is not the same across all cars. On some vehicles it is mounted on the front of the engine near the crankshaft pulley. On others it sits on the side of the block, and on a few it is at the rear near the transmission. Your owner's manual or a repair guide for your make, model, and year will show you exactly where.

Once you find it, note what is blocking access. You may need to remove the wheel well liner, unbolt the engine cover, or move hoses and wiring out of the way. Take a photo with your phone before you disconnect anything, so you can see how the connector and wiring route back to the engine bay.

Disconnect the battery and remove the old sensor

Disconnect the negative terminal of your battery first. This prevents accidental short circuits while you work. Then locate the electrical connector on the sensor and press the release tab or clip to unplug it. Some connectors are tight; wiggle gently rather than pulling hard.

The sensor itself is held in place by a single bolt, usually 10mm or 13mm. Use a socket wrench to remove it. If the sensor is stuck, explore penetrating oil around the base and wait 10 to 15 minutes before trying again. Once the bolt is out, the sensor should slide straight out of its hole. If it does not, rock it gently side to side rather than twisting.

Install the new sensor and reconnect everything

Before you insert the new sensor, check that the O-ring or rubber seal on the tip is intact and not cracked. If it looks damaged, the part may have been damaged in shipping. Slide the new sensor into the hole and hand-tighten the bolt first. Then use your socket wrench to snug it down firmly but not with all your strength—over-tightening can crack the sensor body.

Reconnect the electrical connector by pushing it straight onto the sensor until you hear or feel a click. Reconnect the negative battery terminal. Do not start the engine yet if you removed any hoses or covers; reinstall those first and double-check that all bolts are tight.

Clear the check engine light and test the engine

Start the engine and listen for any unusual sounds. The engine should turn over smoothly and idle without shaking. If the check engine light is still on, it may take a few complete startup cycles for the computer to recognize the new sensor. Drive the vehicle for 10 to 15 minutes at normal speeds, including some highway driving if possible.

If the light stays on after that, you can clear the code yourself using an OBD-II scanner, which you can rent from most auto parts stores for free. Plug the scanner into the diagnostic port under the steering wheel, select "clear codes," and follow the on-screen prompts. If the light comes back on when ready, the new sensor may be faulty or the wiring to it may be damaged.

Tools and parts you will need

You will need a socket set with 10mm and 13mm sockets, a ratchet wrench, and a socket extension if the sensor is hard to reach. A penetrating oil like PB Blaster or WD-40 helps if the old sensor is stuck. Have a clean rag nearby to wipe away any oil or dirt around the sensor hole before you install the new one.

The crankshaft position sensor itself costs between $50 and $250 depending on your vehicle. OEM (original equipment manufacturer) sensors are usually more expensive but often last longer than aftermarket parts. Check your owner's manual or a parts website to confirm the correct part number for your make and model before you buy.

When to call a mechanic instead

If the sensor is in a location that requires removing the engine cover, intake manifold, or other major components, the job becomes much longer and more complex. Some vehicles also have the sensor mounted in a tight space where standard tools do not fit. In those cases, a mechanic with the right tools and a lift can do the work faster and with less risk of damaging surrounding parts.

If you remove the old sensor and find that the hole is stripped or the threads are damaged, the engine block may need repair before a new sensor can be installed securely. This is rare but does happen on older vehicles. A mechanic can assess the damage and tell you whether the block can be repaired or whether a different mounting solution is needed.

Frequently Asked Questions

Can I drive the car if the crankshaft position sensor is bad?

You can drive it short distances, but the engine may stall without warning or refuse to start. If the sensor has failed completely, the engine will not start at all. Do not rely on a failing sensor for highway driving or long trips.

How do I know if the new sensor is installed correctly?

The engine should start smoothly and idle without shaking. The check engine light should turn off within a few driving cycles. If the light stays on or the engine runs rough, the sensor may not be seated fully or the connector may not be clicked in all the way.

What if the check engine light comes back after I clear the code?

The new sensor may be faulty, the wiring to the sensor may be damaged, or there may be a different problem causing the same code. Use an OBD-II scanner to read the code again and confirm it is the same one. If it is, the sensor itself may need to be replaced under warranty.

Do I need to reset the engine computer after replacing the sensor?

No. The computer will recognize the new sensor automatically once you start the engine. The check engine light may stay on for a few driving cycles while the computer relearns the sensor's signal, but it should turn off on its own.

Can a bad crankshaft position sensor damage other engine parts?

A failing sensor will not damage other parts directly, but a completely failed sensor can cause the engine to stall or misfire, which puts stress on the transmission and starter. Replace it as soon as you notice symptoms to avoid secondary damage.