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 at any given moment. The engine uses this signal to time the spark plugs and fuel injectors correctly. Without an accurate signal, your engine will not start, will run rough, or will shut off while driving.
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 connector corrodes, and the signal becomes weak or disappears entirely. A failed sensor is one of the most common reasons an engine cranks but will not start.
Key Takeaways
- The crank position sensor is located near the crankshaft or crankshaft pulley, usually on the front, back, or side of the engine block depending on your vehicle.
- You will need basic hand tools (socket set, wrenches, screwdrivers), a new sensor matched to your vehicle's year and model, and sometimes a jack and jack stands if the sensor is underneath.
- The replacement process takes one to three hours for most vehicles and involves disconnecting the battery, locating the sensor, unbolting it, unplugging the connector, and installing the new one in reverse order.
- After installation, you may need to clear the engine fault code with a diagnostic scanner or by disconnecting the battery for several minutes, depending on your vehicle.
- If the engine still will not start after replacement, the problem may be a wiring issue, a bad connector, or a different fault — not the sensor itself.
Locate the sensor on your vehicle
The location of the crank position sensor varies by make, model, and year. On many vehicles it sits on the front of the engine block near the crankshaft pulley. On others it is mounted on the back of the engine, near the transmission bell housing. Some are tucked underneath, requiring you to raise the vehicle and remove the wheel well liner or splash guard.
The best way to find it is to consult your vehicle's service manual or search online for "[your year, make, model] crank position sensor location." Once you know where it is, you can decide whether you need to lift the vehicle or remove other components to reach it. If the sensor is underneath or behind other parts, you may want to take photos before you start so you can remember how everything fits back together.
Disconnect the battery and remove the old sensor
Before you touch anything electrical, disconnect the negative terminal of the battery. Use a wrench to loosen the nut on the negative cable and slide it off the battery post. This prevents accidental shorts and protects the engine computer.
Once the battery is disconnected, locate the electrical connector on the sensor 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. Next, use the correct socket or wrench to remove the bolt or bolts holding the sensor to the engine block. Most sensors have one or two bolts. Keep the bolts in a safe place — you will reuse them. Slide the sensor out of its mounting hole.
Install the new sensor and reconnect the connector
Before you install the new sensor, compare it to the old one to make sure they are the same. The connector, the body shape, and the mounting holes should match. If they do not, you have the wrong part — stop and get the correct sensor.
Slide the new sensor into the mounting hole and align the bolt holes. Thread the bolts by hand first to avoid cross-threading, then tighten them with your socket or wrench. The bolts do not need to be tight — snug is enough. Over-tightening can crack the sensor body. Plug the electrical connector back into the sensor until you hear or feel it click into place. The connector should be fully seated and not wiggle.
Reconnect the battery and clear the fault code
Reconnect the negative battery cable and tighten the nut. The engine computer may have stored a fault code for the old sensor. On some vehicles, the code clears on its own after a few driving cycles. On others, you will need to clear it manually using a diagnostic scanner (also called a code reader), which you can borrow or rent from many auto parts stores.
If you do not have a scanner, you can try disconnecting the negative battery cable for 10 to 15 minutes. This drains the computer's memory and clears the code on many vehicles, though not all. Once the code is cleared, start the engine and listen for rough running or misfires. The engine should start and idle smoothly. If it does not, the problem may be elsewhere.
What to do if the engine still will not start
If you have installed a new sensor and the engine still will not start or cranks but does not fire, the fault may not be the sensor itself. Check that the electrical connector is fully seated and not loose. Wiggle it gently while someone tries to start the engine — if the engine catches, the connector is not making good contact and may need to be cleaned or replaced.
If the connector is tight and the engine still will not start, the wiring between the sensor and the engine computer may be damaged, or the computer itself may have a fault. At this point, a diagnostic scanner becomes necessary to read the fault code and pinpoint the real problem. Many auto parts stores will read the code for free. If the code points to the crank position sensor circuit rather than the sensor itself, you are dealing with a wiring or connector issue that may require professional help.
Tools and parts you will need
| Item | Why you need it |
|---|---|
| New crank position sensor (matched to your vehicle) | The replacement part; must be the correct year, make, and model |
| Socket set and wrenches | To remove and install the mounting bolts |
| Screwdrivers (flathead and Phillips) | To remove splash guards or other panels if needed |
| Jack and jack stands (if sensor is underneath) | To safely raise the vehicle and support it while you work |
| Diagnostic scanner (optional) | To clear the fault code after installation; many auto parts stores lend these free |
Frequently Asked Questions
How do I know if my crank position sensor is bad?
Common signs are an engine that cranks but will not start, a check engine light, rough idle, stalling while driving, or sudden loss of power. A diagnostic scanner will show a fault code related to the crankshaft position sensor circuit. If you see code P0335, P0336, P0337, or similar, the sensor or its wiring is the likely culprit.
Can I drive with a bad crank position sensor?
No. Once the sensor fails completely, the engine will not start or will shut off when ready. If the sensor is failing intermittently, you may be able to drive short distances, but the engine will stall without warning. Do not rely on a failing sensor — replace it as soon as you can.
Do I need to replace the crankshaft pulley or timing belt when I replace the sensor?
No. The sensor only reads the pulley or the crankshaft itself; it does not wear out the pulley or belt. Replace the sensor alone unless your vehicle has other maintenance due at the same time.
What if the new sensor has a different connector than the old one?
Stop and verify you have the correct part. A different connector means you have the wrong sensor for your vehicle. Return it and get the correct one. Forcing a wrong connector can damage the wiring harness.
How much does a crank position sensor cost?
The sensor itself typically costs between $40 and $150 depending on the vehicle. Labor at a shop usually runs $150 to $400. Doing the work yourself saves the labor cost but requires basic tools and mechanical confidence.