What a crank position sensor does and why it fails
Your crank position sensor tells your engine computer where the crankshaft is at any given moment. The computer uses that signal to time the fuel injectors and ignition spark. When the sensor fails, your engine won't start, or it will stall while you're driving because the computer has no idea when to fire the cylinders.
These sensors fail because they sit near heat and vibration. The wiring corrodes, the connector loosens, or the sensor itself wears out. You'll usually see a check engine light, trouble code P0335 (crankshaft position sensor malfunction), or both. Some cars will crank but not start at all.
Replacement is straightforward on most vehicles — usually 30 minutes to an hour if you have basic tools. The sensor itself costs $50 to $250 depending on your car's make and model. Labor at a shop runs $150 to $400.
Key Takeaways
- The crank position sensor sits near the crankshaft, usually on the engine block or inside the distributor, and you'll need to locate it using your vehicle's service manual or a repair database.
- You'll need a socket set, screwdrivers, and possibly a sensor socket or a thin wrench, depending on how the sensor is mounted in your specific vehicle.
- Disconnect the negative battery terminal before you start work to prevent electrical shorts and accidental engine cranking.
- The sensor unplugs from a connector and unscrews from its mounting location; installation is the reverse, but you must not overtighten the fastener or you'll crack the sensor body.
- After installation, clear the check engine light with a code reader or by disconnecting the battery for 15 minutes, then test-drive to confirm the light stays off.
Locate the sensor using your vehicle's manual or repair information
The crank position sensor location varies by engine design. On some cars it's bolted to the outside of the engine block near the crankshaft pulley. On others it's inside the distributor or mounted on the transmission bell housing. A few sit deep in the engine bay where you'll need to remove other components first.
Your best source is the vehicle's service manual — either the printed one in your glove box, a factory manual you can buy, or a subscription service like AllData or Mitchell1. If you don't have access to those, search "[your year, make, model] crank position sensor location" on a repair forum or YouTube. Write down the exact location and any components you need to remove to reach it.
Take a photo of the sensor's location and connector before you disconnect anything. This helps you remember which way the connector faces and whether any brackets or wires are in the way.
Gather tools and disconnect the battery
You'll need a socket set (usually 8mm to 10mm), screwdrivers (Phillips and flat-head), and possibly a sensor socket — a thin-walled socket designed to fit over the sensor body without hitting surrounding parts. Some sensors unscrew with a regular wrench instead. Check your manual to see which fastener size your sensor uses.
Before touching anything electrical, disconnect the negative battery terminal. Loosen the nut on the negative post with a wrench, slide the cable off, and set it aside where it won't touch metal. This prevents accidental shorts and stops the engine from cranking if you bump the starter.
Let the engine cool for at least 30 minutes if you've been driving. The sensor and surrounding metal get hot enough to burn your hand.
Unplug the connector and remove the old sensor
Locate the electrical connector on the sensor. It usually has a small tab or clip you press to release it. Push that tab and pull the connector straight away from the sensor. If it's stuck, wiggle it gently side to side — don't yank on the wires.
Now unscrew the sensor from its mounting. Use the socket or wrench that fits the fastener head. Turn counterclockwise. The sensor usually has one bolt, though some have two. Once the fastener is loose, unscrew it by hand and set it aside in a safe place — you'll reuse it.
Slide the sensor out of its hole. Some sensors come out straight; others need to be angled or rotated slightly. If it's stuck, don't force it. Wiggle it gently while pulling, or spray a small amount of penetrating oil around the base and wait five minutes.
Install the new sensor and reconnect the wiring
Before you install the new sensor, compare it to the old one. They should look identical — same shape, same connector type, same mounting hole. If they don't match, you've ordered the wrong part.
Slide the new sensor into the mounting hole. It should fit smoothly without forcing. Once it's seated, thread the fastener by hand first to make sure you're not cross-threading it. Then use your socket or wrench to tighten it. Tighten firmly but do not over-tighten — you're aiming for snug, not maximum force. Over-tightening can crack the sensor body or strip the threads. Most sensors need only 10 to 15 foot-pounds of torque; if your manual specifies a torque value, use a torque wrench.
Plug the electrical connector back onto the sensor. You should hear or feel a click when it seats fully. Tug on the connector gently to confirm it's locked in place.
Reconnect the battery and clear the check engine light
Slide the negative battery cable back onto the negative post and tighten the nut. Don't over-tighten — hand-tight plus a quarter turn is enough.
Start the engine. It should crank and run normally. If it doesn't start, or if it starts but runs rough, turn it off and double-check that the connector is fully seated and the sensor fastener is tight.
The check engine light may stay on for a few driving cycles while the computer relearns the sensor signal. If you want to clear it when ready, use an OBD2 code reader (available at auto parts stores for $25 to $100, or borrow one). Plug it into the diagnostic port under the steering wheel, select "Clear Codes," and follow the prompts. Alternatively, disconnect the negative battery terminal again for 15 minutes — this clears the code on most vehicles, though not all.
Drive the car for 20 to 30 minutes at normal speeds. The light should stay off. If it comes back on, the new sensor may be defective, or there may be another problem with the ignition or fuel system.
When to call a mechanic instead
If the sensor is in a location that requires removing the intake manifold, cylinder head cover, or other major components, the job becomes much longer and more complex. A mechanic with a lift and the right tools can do it faster and safer than you can in a driveway.
If you don't have a code reader and the check engine light won't clear after 30 days of driving, a shop can clear it for you — usually a $50 to $100 charge. If the light comes back on within a week, the sensor may be bad, or the wiring may be damaged. A mechanic can test the sensor and wiring with a multimeter to confirm.
If you're not comfortable working around the engine bay or disconnecting electrical connectors, there's no shame in taking it to a shop. A bad sensor is a straightforward repair, and most mechanics charge a flat rate rather than hourly labor.
Frequently Asked Questions
Can I drive with a bad crank position sensor?
No. Once the sensor fails completely, the engine won't start or will stall when ready. Some cars will limp along for a few miles if the sensor is intermittent, but you shouldn't rely on it. Have it replaced as soon as you confirm that's the problem.
How do I know if it's the crank sensor and not something else?
A code reader will show you trouble code P0335 or a related code (P0336, P0337, P0338). If you don't have a reader, a shop can scan it for $50 to $100. If the code points to the crank sensor and the engine won't start or stalls while driving, the sensor is almost certainly the problem.
Do I need to reset anything after I install the new sensor?
No. The computer will recognize the new sensor automatically once you start the engine. You only need to clear the old fault code so the check engine light turns off. Some cars do this on their own after a few driving cycles; others need a code reader to clear it manually.
What if the new sensor doesn't fix the problem?
First, confirm the connector is fully seated and the fastener is tight. If the engine still won't start or runs rough, the wiring may be damaged, the connector may be corroded, or there may be a separate ignition or fuel system problem. Use a multimeter to test the wiring for continuity, or take it to a shop for diagnosis.
Can I reuse the old fastener?
Yes, in most cases. The fastener is usually a straightforward bolt or screw that doesn't wear out. If it's stripped, rusted, or damaged, buy a replacement at a hardware store — it's typically an inexpensive bolt in a common size like M6 or M8.