What a crankshaft sensor does and why it fails

Your crankshaft sensor tells your engine's computer where the crankshaft is positioned 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.

Crankshaft sensors fail because they wear out over time — they sit near heat and vibration — or because the wiring corrodes. Most last between 80,000 and 150,000 miles, though this varies by vehicle and driving conditions. A failed sensor cannot be repaired; it must be replaced.

Key Takeaways

  • The crankshaft sensor is usually bolted to the engine block near the crankshaft pulley, and you will need to remove the pulley or timing cover to reach it.
  • You will need basic hand tools (socket set, wrenches, screwdrivers), a jack and jack stands if you are working underneath, and possibly a pulley removal tool depending on your vehicle.
  • Disconnect the negative battery terminal before you start to prevent electrical shock and accidental engine starting.
  • The job typically takes two to four hours for a DIY mechanic, though some vehicles require removing the wheel well or timing cover, which adds time.
  • If you are not comfortable working under a running vehicle or removing engine covers, a shop can do this work for $150 to $400 depending on your car's design.

Locate the sensor on your specific vehicle

The crankshaft sensor location varies widely. On some cars it bolts to the front of the engine block near the crankshaft pulley. On others it sits inside the timing cover or near the oil pan. Your vehicle's service manual will show the exact location and how to access it — you can find the manual online for free at sites like AllData or your manufacturer's website, or buy a printed copy from an auto parts store.

Before you start, take a photo of the sensor and its wiring with your phone. This helps you reconnect the new sensor correctly and remember which way it faced. If you cannot see the sensor without removing other parts, note what needs to come off first — often the serpentine belt, crankshaft pulley, or timing cover.

Gather tools and disconnect the battery

You will need a socket set, wrenches, screwdrivers, and a jack with jack stands if you are working underneath the vehicle. Some vehicles require a crankshaft pulley removal tool (a three-jaw puller) to get the pulley off without damaging it. Check your manual to see if you need one before you start; if you do, you can rent one from an auto parts store for $20 to $40.

Disconnect the negative battery terminal first. Loosen the nut on the negative post with a wrench, slide the cable off, and set it aside where it cannot touch the post again. This prevents electrical shock and stops the engine from accidentally starting while you work.

Remove the crankshaft pulley if necessary

On many vehicles, the crankshaft pulley blocks access to the sensor. To remove it, you first need to remove the serpentine belt — loosen the tensioner bolt and slide the belt off the pulleys. Take a photo of the belt routing before you remove it so you know how to put it back on.

Next, remove the bolt holding the pulley to the crankshaft. This bolt is very tight; you may need to lock the engine in place so it does not spin while you loosen it. Some shops use a strap wrench or a breaker bar with a socket. Once the bolt is out, use a three-jaw puller to pull the pulley straight off the crankshaft. Do not pry it off with a screwdriver, as this can damage the crankshaft.

Unplug and unbolt the old sensor

Once you can see the sensor, locate the electrical connector and press the release tab or clip to unplug it. The connector should slide off without force. If it is stuck, wiggle it gently side to side rather than pulling straight.

The sensor is held in place by one or two bolts. Use the correct socket or wrench size — using the wrong size can strip the bolt head. Remove the bolts and slide the sensor out. Some sensors have a rubber O-ring or gasket; if yours does, note whether it comes off with the sensor or stays in the hole. If it stays, remove it and clean the hole with a rag.

Install the new sensor and reconnect everything

Slide the new sensor into the hole and hand-tighten the bolts first to make sure the sensor sits straight. Then tighten the bolts with your wrench or socket — do not over-tighten, as this can crack the sensor. Most sensors need only 15 to 25 foot-pounds of torque; check your manual for the exact number.

Plug the electrical connector back in until you hear or feel it click. Reconnect the crankshaft pulley by reversing the removal steps: use the three-jaw puller to press the pulley back onto the crankshaft, install the bolt, and tighten it to the torque spec in your manual (usually 80 to 150 foot-pounds). Reinstall the serpentine belt, using your photo as a guide. Reconnect the negative battery terminal.

Start the engine and clear the check engine light

Turn the key to start the engine. It should start normally and run smoothly. If the engine cranks but does not start, turn the key off and check that the sensor connector is fully seated and the bolts are tight. If it still does not start, the sensor may be defective or you may have a wiring problem — in this case, take the car to a shop.

If the engine starts and runs, the check engine light may still be on from the old fault code. You can clear it yourself with an OBD-II scanner (available at auto parts stores for $25 to $100), or you can drive the car for a few days and the light may clear on its own. If the light comes back on, there may be another problem; have a shop scan the code to find out what it is.

Frequently Asked Questions

Can I replace the crankshaft sensor without removing the crankshaft pulley?

On some vehicles, yes — the sensor is accessible from the side or top without removing the pulley. On others, the pulley is in the way. Your service manual will show whether you need to remove it. If you are not sure, start by trying to reach the sensor without removing the pulley; if you cannot, then remove it.

What if the new sensor does not stop the check engine light?

The light may take a few drive cycles to clear on its own, or you may need to use an OBD-II scanner to clear the code manually. If the light comes back on after a few days of driving, the new sensor may be defective, or there may be a wiring or connector problem. Have a shop scan the code to see what fault it is reporting.

How much does a crankshaft sensor cost?

The sensor itself usually costs $40 to $150 depending on your vehicle make and model. Labor at a shop typically runs $100 to $300. If your car requires removing the timing cover or other major components, labor can be higher. Call a few shops for quotes before you decide whether to do it yourself or have it done.

Do I need to replace the gasket or O-ring when I install the new sensor?

If the old gasket or O-ring came off with the sensor, install a new one with the new sensor — it is usually included in the sensor kit or costs a few dollars. If the gasket stayed in the hole, you can reuse it if it is not cracked or flattened. If it looks damaged, replace it to prevent oil leaks.