What a crankshaft position sensor does and why it fails
A crankshaft position sensor tells your engine's computer where the crankshaft is at any given moment. The computer uses this information to time the spark plugs and fuel injectors correctly. Without an accurate signal, your engine cannot run properly — it may stall, misfire, or fail to start at all.
The sensor sits near the crankshaft, usually mounted on the engine block or transmission bell housing, and reads a toothed ring as the crankshaft rotates. Over time, the sensor's internal electronics wear out, or the connector corrodes, or the ring itself becomes damaged. Once the signal becomes unreliable, the computer cannot trust the timing data and the engine runs rough or shuts down.
Replacement is straightforward on most vehicles — the sensor itself costs between $50 and $200, and labor typically runs $100 to $300 depending on how accessible the sensor is on your engine. Some vehicles require removing other components to reach it, which adds time and cost.
Key Takeaways
- The crankshaft position sensor sends timing data to your engine computer; a failed sensor causes hard starts, stalling, or a check engine light.
- Replacement cost ranges from $150 to $500 total, depending on the vehicle and how difficult the sensor is to reach.
- You can replace the sensor yourself if you have basic tools and mechanical confidence, or take it to a shop for professional installation.
- A scan tool can confirm the sensor has failed by reading the diagnostic code from your computer before you buy parts.
- Ignoring a failed sensor risks engine damage and leaves you stranded, so replacement should not be postponed once symptoms appear.
Symptoms that point to a failing crankshaft position sensor
The most common sign is a check engine light on your dashboard. When the sensor signal drops out or becomes erratic, the computer logs a code — usually P0335, P0336, P0337, or P0338 depending on the specific fault. A scan tool will read this code and confirm the sensor is the problem.
Before the light comes on, you may notice the engine cranks but does not start, or starts and then stalls when ready. The engine may also run rough at idle or hesitate under acceleration. In some cases, the vehicle will die while driving and refuse to restart until it cools down — a sign the sensor is temperature-sensitive and fails when hot.
If you ignore these symptoms, the engine may not run at all, leaving you unable to drive. Some vehicles will limp along on a default timing setting, but performance suffers and fuel economy drops sharply.
How to confirm the sensor has failed
The most reliable way to confirm failure is to connect a diagnostic scan tool to your vehicle's OBD-II port, located under the steering wheel on the driver's side. The tool reads codes stored in the engine computer. A crankshaft position sensor code will appear as P0335 or a related variant.
If you do not own a scan tool, most auto parts stores will scan your vehicle for free. Bring your keys and vehicle identification number (VIN), which is printed on your dashboard and registration. The scan takes five minutes and costs nothing.
Do not replace the sensor based on symptoms alone — a bad alternator, weak battery, or faulty starter can cause similar hard-start problems. The scan tool eliminates guesswork and saves you from replacing the wrong part.
Sensor location and accessibility on common vehicles
Location varies widely. On many Ford and General Motors vehicles, the sensor bolts to the front of the engine block near the crankshaft pulley, making it relatively straightforward to reach. On some Honda and Toyota models, the sensor sits behind the engine or tucked under the intake manifold, requiring removal of other components first.
Before you buy the part, look up the specific location for your vehicle's year, make, and model in a repair manual or online forum dedicated to your car. This tells you whether you can reach it with basic hand tools in an hour, or whether you need to remove the alternator, air intake, or other assemblies first.
If the sensor is buried deep in the engine bay, labor costs can climb to $300 or more. If it is mounted on the outside of the block, labor may be only $75 to $150. Knowing the location before you commit to the repair helps you decide whether to do it yourself or pay a shop.
DIY replacement versus professional installation
Replacing the sensor yourself requires a socket set, a wrench, and a new sensor. The steps are straightforward: disconnect the battery, unplug the old sensor, unbolt it, bolt in the new one, plug it in, and reconnect the battery. On accessible sensors, the whole job takes 30 to 60 minutes.
The main risk is damaging the connector or the wiring harness if you pull too hard. The connector is plastic and breaks easily. Work slowly, wiggle the connector gently side to side as you pull, and do not yank straight out.
If the sensor is difficult to reach, professional installation saves you frustration and the risk of dropping tools into the engine bay or stripping bolts. A shop has the right tools, knows the common pitfalls for your vehicle, and can clear the diagnostic code after installation. Most shops charge a flat rate for this job, typically $200 to $400 total including the part.
Choosing the right replacement sensor
Buy a sensor designed for your specific vehicle year, make, and model. The part number is printed on the old sensor or listed in your owner's manual. Do not assume all crankshaft position sensors are the same — they are not. A sensor for a 2010 Honda Civic will not work on a 2010 Ford Focus.
OEM (original equipment manufacturer) sensors cost more but are may provide to fit and function. Aftermarket sensors are cheaper and usually reliable, but quality varies by brand. Reputable aftermarket brands include Bosch, Standard Motor Products, and Motorcraft. Avoid no-name sensors from unknown suppliers.
If you buy the wrong sensor by mistake, most auto parts stores will exchange it for free if you have your receipt and the part is unused. Keep the packaging and receipt until you have confirmed the new sensor works.
What happens after replacement
After you install the new sensor and reconnect the battery, start the engine and let it idle for a minute. The check engine light should go out within a few driving cycles. If the light stays on, the code may not have cleared, or there may be a second problem — a bad connector, corroded wiring, or a computer fault.
If the light returns after a few days, take the vehicle back to the shop or scan it again. A recurring code suggests the new sensor is defective, the wiring is damaged, or the computer itself has a fault. Most shops warranty their work for 30 days, so if the problem returns, they will diagnose and fix it at no charge.
Once the sensor is working, your engine should start reliably, idle smoothly, and run without hesitation. Fuel economy should return to normal. If performance issues persist after replacement, have the vehicle scanned again — another sensor or component may be failing.
Frequently Asked Questions
Can I drive with a bad crankshaft position sensor?
Not safely. A failed sensor means your engine cannot time the spark plugs correctly, so it may stall without warning or fail to start. You risk being stranded on the road. Some vehicles limp along on a default timing setting, but performance is poor and fuel economy suffers. Replace the sensor as soon as symptoms appear.
How long does a crankshaft position sensor last?
Most sensors last 100,000 to 150,000 miles, but failure can occur earlier if the sensor is exposed to extreme heat, moisture, or vibration. There is no set maintenance interval — you replace it only when it fails. Some vehicles go 200,000 miles without a problem; others fail at 80,000 miles.
What if I replace the sensor and the check engine light comes back?
The new sensor may be defective, the wiring harness may be damaged, or the connector may be corroded. Have the vehicle scanned again to see if the same code returns or if a different code appears. If the same code returns, the shop should replace the sensor under warranty at no charge.
Is the crankshaft position sensor the same as the camshaft position sensor?
No. The crankshaft sensor monitors the crankshaft rotation; the camshaft sensor monitors the camshaft rotation. Both send timing data to the computer, but they are separate parts in different locations. A vehicle can have both sensors fail independently, and each has its own diagnostic code.
Can a bad battery cause a crankshaft position sensor code?
A weak battery can cause hard starts that feel similar to sensor failure, but it will not trigger a crankshaft position sensor code. If your scan tool shows a P0335 or related code, the sensor or its wiring is the problem, not the battery. However, a weak battery can mask a sensor problem, so charge or replace the battery first if it is low.