What a crankshaft position sensor does and why it fails
A crankshaft position sensor tells your engine's computer where the crankshaft is in its rotation at any given 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 rough 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 over time because it operates in heat and vibration. Most sensors last 80,000 to 150,000 miles, though some fail earlier if the engine runs hot or if the connector corrodes.
You can confirm a bad sensor by having a mechanic read the diagnostic code with a scanner — a code like P0335 or P0336 points directly to this sensor. Some auto parts stores will read codes for free.
Key Takeaways
- The crankshaft position sensor bolts to the engine block near the crankshaft and costs between $150 and $400 in parts and labor at a shop, or $30 to $100 in parts if you do it yourself.
- You will need basic hand tools — usually a socket wrench, screwdrivers, and a new sensor — plus the ability to locate the sensor on your specific engine, which varies by make and model.
- The job takes 30 minutes to two hours depending on sensor location and engine design; some sensors are straightforward to reach, others require removing other components first.
- Disconnecting the battery before you start prevents electrical damage and clears the check engine light once the new sensor is installed and the engine runs.
- If the sensor is stuck or corroded, penetrating oil and patience work better than force, which can break the bolt or damage the engine block.
Gather your tools and locate the sensor on your engine
Before you start, you need to know where the sensor sits on your vehicle. Check your owner's manual or search online for "[your year, make, model] crankshaft position sensor location." The location varies widely — it might be on the front of the engine near the harmonic balancer, on the side of the block, or at the rear near the transmission. Some vehicles have more than one sensor.
Collect these tools: a socket set and ratchet (usually 8mm, 10mm, or 13mm), a screwdriver set, a new crankshaft position sensor (order the correct part number for your vehicle), penetrating oil if the bolt is stuck, and a container to hold small bolts so you do not lose them. You may also need a jack and jack stands if the sensor is underneath the vehicle, or you may need to remove other parts like the air intake or engine cover to reach it.
Park on level ground, engage the parking brake, and let the engine cool completely. Disconnect the negative battery terminal first — this prevents accidental electrical damage and ensures the computer will recognize the new sensor once you start the engine again.
Remove the old sensor step by step
Locate the sensor's electrical connector and unplug it by pressing the release tab or clip. The connector should come free without force. If it is stuck, wiggle it gently side to side rather than pulling straight out.
Use your socket wrench to remove the bolt or bolts holding the sensor to the engine block. Most sensors use one bolt, but some use two. If a bolt will not budge, spray it with penetrating oil, wait 10 to 15 minutes, and try again. Do not force it — a broken bolt in the engine block creates a much larger problem. Once the bolt is loose, unscrew it by hand and set it aside in your container.
Gently pull the sensor straight out of its hole. Some sensors come free easily; others stick because of corrosion or old sealant. If it is stuck, explore more penetrating oil around the base and wait again. Rock it gently side to side, then pull. Once it is out, inspect the hole for debris or corrosion and wipe it clean with a dry cloth.
Install the new sensor and reconnect the electrical connector
Before you insert the new sensor, check whether it has a rubber O-ring or gasket. If it does, leave it in place — do not remove it. If the old sensor left sealant or corrosion in the hole, wipe the hole clean again so the new sensor seats properly.
Insert the new sensor straight into the hole until it stops. Do not force it. Thread the bolt by hand first to avoid cross-threading, then use your socket wrench to tighten it. The bolt should be snug but not over-tightened — typically 15 to 25 foot-pounds of torque, though your manual will specify the exact amount. If you do not have a torque wrench, snug it firmly and stop; over-tightening can crack the sensor or strip the threads.
Plug the electrical connector back in until you hear or feel it click. Make sure the connector is fully seated and the release tab is locked in place.
Reconnect the battery and test the engine
Reconnect the negative battery terminal by tightening the bolt on the terminal clamp. Start the engine and listen for any unusual sounds. The engine should start normally and idle smoothly. If the check engine light was on before, it should turn off after the engine runs for a minute or two — the computer recognizes the new sensor and clears the old fault code.
If the check engine light stays on or the engine still runs rough, turn off the engine and double-check that the connector is fully seated and the bolt is tight. If those are correct, the new sensor may be defective, or there may be a second problem — have a mechanic scan the code again to confirm.
Take the vehicle for a short test drive to confirm normal operation. If everything runs smoothly, the job is complete.
When to stop and call a mechanic
If the sensor bolt is stuck and penetrating oil does not free it after several attempts, stop. Forcing a stuck bolt risks breaking it inside the engine block, which requires removing the block to repair. A mechanic has better tools and experience to extract a stuck bolt without damage.
If the sensor is in a location that requires removing the intake manifold, transmission, or other major components, the labor cost at a shop may be lower than the time and risk of doing it yourself. Check a repair manual for your vehicle to see what else must come off first.
If the new sensor does not solve the problem and the check engine light returns, the issue may be a wiring problem, a corroded connector, or a computer fault. A mechanic with a diagnostic scanner can pinpoint the real cause.
Frequently Asked Questions
How much does a crankshaft position sensor cost?
The sensor itself costs $30 to $100 depending on your vehicle's make and model. Labor at a shop typically runs $120 to $300, so a full replacement at a shop is usually $150 to $400. Doing it yourself saves the labor cost but requires your time and the correct tools.
Can I drive with a bad crankshaft position sensor?
You can drive short distances, but the engine may stall, hesitate, or fail to start. Some vehicles will not start at all if the sensor is completely dead. Do not rely on a failing sensor for highway driving or long trips — have it replaced as soon as you confirm it is the problem.
Will replacing the sensor clear the check engine light?
The light should turn off after the new sensor is installed and the engine runs for a minute or two. If it stays on, the connector may not be fully seated, the bolt may be loose, or there may be a second problem. A mechanic can scan the code again to see what is still triggering the light.
What if I cannot find the sensor on my engine?
Search online for your specific year, make, and model with "crankshaft position sensor location" — forums and repair manuals often have photos showing exactly where it sits. If you still cannot locate it, a mechanic can show you in person, which may be worth the cost of a quick diagnostic visit.
Do I need a torque wrench to install the new sensor?
A torque wrench is helpful but not required for most home mechanics. If you do not have one, snug the bolt firmly with your socket wrench and stop — do not over-tighten. Most crankshaft position sensor bolts are not critical to torque specification the way head bolts are, so hand-tight plus a quarter turn is usually sufficient.