What a crank position sensor does and why it matters

Your crank position sensor tells your engine computer where the crankshaft is at any given moment. The computer uses this information to time the fuel injection and spark plugs correctly. If the sensor fails, your engine will not start, will stall while running, or will run so poorly that your check engine light comes on.

The sensor sits near the crankshaft, usually on the front, side, or rear of the engine depending on your vehicle's design. It reads a toothed ring or magnet on the crankshaft as it spins. When the sensor stops sending a clear signal, the computer cannot do its job.

You can test whether the sensor itself is working before you pay a mechanic to replace it. The test takes about 30 minutes and requires only a multimeter — a tool that costs $15 to $30 at any auto parts store.

Key Takeaways

  • A crank position sensor failure usually shows up as a no-start condition, rough idle, or a check engine light with a code in the P0300s range.
  • You can test the sensor with a multimeter by checking for voltage output while the engine cranks, which tells you whether the sensor is generating a signal.
  • A resistance test with the multimeter can reveal whether the sensor's internal wiring is broken, though this test is less reliable than a voltage test.
  • If the sensor passes the voltage test but the engine still will not start, the problem is likely in the wiring between the sensor and the computer, not the sensor itself.
  • Crank position sensors typically cost $50 to $300 depending on the vehicle, and replacement usually takes one to three hours at a shop.

Locate your sensor before you test it

The crank position sensor location varies widely. On some vehicles it is mounted on the front of the engine near the crankshaft pulley. On others it sits on the side of the engine block or tucked behind the engine near the transmission bell housing. A few vehicles have the sensor mounted inside the distributor or on the camshaft instead.

Check your vehicle's service manual or search online for "[your year, make, model] crank position sensor location" to find the exact spot. Once you locate it, you will see a cylindrical or rectangular sensor with an electrical connector on one end. The connector usually has two or three wires running to it.

Before you disconnect anything, take a photo of the connector with your phone so you remember which wire goes where. Write down the wire colors if they are visible.

Test for voltage output while the engine cranks

This is the most reliable test because it shows whether the sensor is actually generating a signal when the crankshaft is turning. Set your multimeter to DC voltage mode (usually marked with a V and a straight line with dots underneath). The range should be set to 20 volts or higher.

Disconnect the sensor's electrical connector by gently pulling it straight out. Do not twist or force it. Locate the two or three pins inside the connector and identify which one is the signal wire. Your service manual will show you this, or you can search online for a wiring diagram for your vehicle. The signal wire is usually the middle pin or the one marked "signal" in the diagram.

Have a helper sit in the driver's seat while you hold one multimeter probe on the signal wire pin and the other probe on a clean metal part of the engine block (ground). Tell your helper to turn the key to the start position and crank the engine for about five seconds. Watch the multimeter display. You should see the voltage fluctuate between roughly 0 and 5 volts as the crankshaft spins. If the display stays at zero or does not move, the sensor is not generating a signal and is likely faulty.

Check the sensor's resistance if voltage testing is unclear

If you cannot get a clear voltage reading or want a second confirmation, you can test the sensor's internal resistance. This tells you whether the coil inside the sensor is broken. Reconnect the sensor's connector first, then disconnect it again and set your multimeter to resistance mode (marked with an Ω symbol).

Hold one probe on each of the two main pins inside the connector (not the ground pin if there is a third one). The resistance should read between 200 and 900 ohms, depending on your sensor type. Check your service manual for the exact range for your vehicle. If the reading is zero, very high, or shows "OL" (open line), the sensor's internal coil is broken.

Keep in mind that a resistance test only tells you whether the coil is intact. It does not tell you whether the sensor is actually working under real engine conditions. A voltage test is more reliable.

Inspect the wiring and connector for damage

While you have the connector disconnected, look inside it for corrosion, bent pins, or water damage. Corrosion appears as a white, green, or blue crusty coating on the pins. Bent pins will not make good contact even if the sensor itself is fine. If you see corrosion, you can sometimes clean it gently with a small brush or contact cleaner, but often the connector needs to be replaced.

Follow the wires from the sensor back toward the engine computer (usually mounted on the firewall or under the hood near the battery). Look for cuts, pinches, or places where the insulation is worn through. Rodents sometimes chew through sensor wires, and heat or rubbing can damage them over time. If you find damaged wiring, that is your problem, not the sensor.

Check that the connector clicks firmly back into place when you reconnect it. A loose connection will cause the same symptoms as a failed sensor.

What to do if the sensor passes the tests

If your voltage test shows a good signal and your resistance test is in range, the sensor itself is working. The problem is likely in the wiring between the sensor and the engine computer, a bad connector, or a computer fault. At this point, you should have a mechanic check the wiring with a scope or take the vehicle to a shop that can read the computer codes in detail.

If the sensor fails either test, it needs to be replaced. Replacement is straightforward on most vehicles — usually two bolts and one connector. The sensor itself costs $50 to $300 depending on whether you buy an original part or an aftermarket one. Labor at a shop typically runs $100 to $200.

Frequently Asked Questions

What does a bad crank position sensor code look like?

The most common code is P0335, which means "Crankshaft Position Sensor Circuit." You may also see P0336 (circuit range or performance), P0337 (circuit low), or P0338 (circuit high). Codes in the P0300s range usually point to the crank sensor, but they can also mean bad wiring or a computer problem. A voltage test on the sensor itself will narrow it down.

Can a crank position sensor fail partially?

Yes. A sensor can work when the engine is cold but fail when it heats up, or it can send a weak signal that the computer sometimes misses. This is why a voltage test while cranking is more useful than a resistance test — it shows whether the sensor works under actual conditions. If the voltage is erratic or very low, the sensor is failing.

Will a bad crank sensor damage the engine?

No. A failed crank sensor will prevent the engine from starting or cause it to stall, but it will not cause mechanical damage. The engine straightforward will not run because the computer cannot time the ignition and fuel. Once you replace the sensor, the engine will run normally again.

Do I need a special tool to replace the sensor?

Usually not. Most crank sensors bolt on with a single bolt or two bolts and take less than an hour to swap out. Some vehicles require you to remove other components to reach the sensor, which adds time. Check your service manual or search online for your specific vehicle to see whether special tools or disassembly is needed.