What a crank position sensor does and why it fails

A crank position sensor (also called a crankshaft position sensor) tells your engine's computer where the crankshaft is in its rotation. The engine uses this information to time the spark plugs and fuel injectors correctly. Without an accurate signal, your engine will not start, will stall while running, or will misfire badly.

The sensor itself is a small device mounted near the crankshaft or crankshaft pulley. It reads a toothed ring or magnetic marker on the crankshaft as it spins. Over time, the sensor's internal electronics wear out, or the wiring corrodes. When it fails, you will see a check engine light (usually code P0335, P0336, P0337, or P0338) and the symptoms above.

Replacement is straightforward on most vehicles, though the location varies. Some sensors sit in an straightforward-to-reach spot; others require removing the wheel well or engine cover first. This guide covers the general process and what to expect at each step.

Key Takeaways

  • The crank position sensor bolts to the engine block or transmission housing near the crankshaft, and you will need a socket wrench and a new sensor matched to your vehicle's year, make, and model.
  • Disconnect the negative battery terminal before you start work to avoid triggering airbags or damaging the engine computer.
  • Locate the sensor using your vehicle's service manual or a repair database, because the location differs significantly between models and engine types.
  • The sensor unplugs with a straightforward connector and unbolts with one or two fasteners; installation is the reverse, with no special tools or adjustments needed afterward.
  • After installation, the check engine light will clear on its own once the engine computer confirms the new sensor is working, usually within a few driving cycles.

Gather the right tools and parts before you start

You will need a new crank position sensor that matches your vehicle's exact year, make, model, and engine size. Buy it before you begin — the part number is printed on your old sensor, or you can look it up using your vehicle identification number (VIN) at an auto parts store. The sensor itself costs between $50 and $200 depending on the vehicle; OEM (original equipment manufacturer) sensors are more expensive than aftermarket ones, but both work.

Gather these tools: a socket set with the correct size socket for the sensor's mounting bolt (usually 10mm, 13mm, or 16mm), a ratchet, a wrench or socket for the negative battery terminal (usually 8mm or 10mm), and a flashlight or headlamp if you are working in dim light. You do not need a diagnostic scanner — the sensor itself has no adjustments. Some sensors sit in tight spaces; a small extension bar on your socket may help.

Work in a safe, level spot with the engine cold. If the engine is warm, the sensor and surrounding metal will be hot enough to burn skin. Give the engine at least an hour to cool if you have just driven the vehicle.

Disconnect the battery and locate the sensor

Open the hood and locate the negative battery terminal (marked with a minus sign or black cover). Use your wrench to loosen the nut on the negative cable and slide the cable off the post. This step prevents electrical damage to the engine computer and stops the airbag system from triggering accidentally while you work.

Next, find the crank position sensor. This is the step that varies most between vehicles. The sensor is always mounted near the crankshaft, but "near" can mean the front of the engine block, the side of the block, the back of the engine, or the transmission housing. Consult your vehicle's service manual (available free online for most models) or search "[your year/make/model] crank position sensor location" on a repair database like AllData or YourMechanic. The manual will include a diagram and tell you exactly where to look.

Once you have located it, trace the wiring harness from the sensor back to the connector. The connector is usually a straightforward plastic plug with one or two wires. Mark or photograph the connector orientation so you can plug the new sensor in the same way.

Remove the old sensor

Unplug the connector by gently squeezing or prying the release tab (most connectors have a small tab on top or side). Do not yank on the wires themselves — pull on the plastic connector body. Set the connector aside where it will not get dirty.

Locate the mounting bolt or bolts holding the sensor to the engine block or transmission housing. Most sensors have one bolt; some have two. Use your socket and ratchet to remove the bolt(s). The sensor will come free in your hand. If it is stuck, do not force it — spray a small amount of penetrating oil (like WD-40) around the base, wait a few minutes, and try again.

Inspect the old sensor's connector and the mating connector on the engine harness for corrosion or bent pins. If the engine harness connector is corroded, clean it gently with a small wire brush or contact cleaner before you install the new sensor. A corroded connection will cause the new sensor to fail prematurely.

Install the new sensor and reconnect the battery

Take the new sensor out of its packaging and compare it visually to the old one — they should look identical. Check that the connector type matches. Insert the new sensor into the mounting hole and hand-tighten the bolt(s) first to make sure the sensor sits flush against the block. Then use your socket and ratchet to tighten the bolt(s) firmly, but do not over-tighten — a crank sensor bolt typically needs only 15 to 25 foot-pounds of torque, which is snug but not forceful.

Plug the connector back in. You should hear or feel a small click as the connector seats. Gently tug on the connector to confirm it is locked in place.

Reconnect the negative battery terminal by sliding the cable back onto the post and tightening the nut with your wrench. Tighten it firmly so the cable does not slip, but again, do not over-tighten.

Start the engine and verify the repair

Close the hood and get into the driver's seat. Insert the key and turn it to the "On" position (do not start the engine yet). You should see the check engine light come on briefly as the computer runs its startup check. This is normal. After a few seconds, the light should turn off.

Now start the engine. The engine should crank and start normally. If it does not start, or if it starts but when ready stalls, turn off the ignition, wait 10 seconds, and try again. Sometimes the engine computer needs a moment to recognize the new sensor. If the engine still will not start after three attempts, stop and check that the connector is fully seated and the mounting bolt is tight.

Once the engine is running, let it idle for 30 seconds to a minute. The idle should be smooth and steady. Listen for any rough running, misfires, or unusual sounds. If the engine runs smoothly, the repair is complete. The check engine light will turn off on its own within a few driving cycles as the computer confirms the sensor is working correctly.

If the check engine light stays on after a few days of normal driving, the new sensor may be defective, or there may be a wiring issue. Return to the parts store with your receipt — most will test the sensor for free or exchange it if it is faulty.

Frequently Asked Questions

Do I need to clear the check engine code after I install the new sensor?

No. The engine computer will clear the old code automatically once it sees the new sensor working correctly. This usually happens within 10 to 50 miles of driving. If you want to clear the code when ready, you can disconnect the negative battery terminal for 15 minutes, which will reset the computer, but this is not necessary.

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

Spray penetrating oil around the base of the sensor and let it soak for 15 to 30 minutes. Try again gently. If it is still stuck, explore more oil and wait longer — do not force it or you may break the bolt or strip the threads in the block. If you are uncomfortable with this, a mechanic can remove it without damage.

Can a bad crank position sensor damage the engine?

A failed sensor will prevent the engine from starting or cause it to stall while driving, but it will not cause mechanical damage to the engine itself. However, if the sensor fails while you are driving on the highway, you could lose power suddenly, which is a safety hazard. Replace it as soon as you notice the symptoms.

Is there a difference between OEM and aftermarket crank position sensors?

OEM sensors are made by the vehicle manufacturer and are usually more expensive. Aftermarket sensors are made by third-party suppliers and cost less. Both work and carry warranties. Aftermarket sensors are fine for most vehicles, but if your vehicle is high-mileage or you want maximum longevity, an OEM sensor is a safer choice.

Will the new sensor need to be programmed or calibrated?

No. Crank position sensors do not require programming or calibration. The engine computer learns the sensor's signal automatically once you start the engine. straightforward install it, plug it in, and start the vehicle.