What a crank sensor does and why it matters

Your crank sensor tells your engine's computer where the crankshaft is positioned at any given moment. The engine uses this information to time the spark plugs and fuel injectors correctly. When the crank sensor fails, your engine cannot fire at the right time, so you get a rough idle, stalling, hard starting, or no start at all.

A failing crank sensor usually triggers the check engine light and stores a diagnostic trouble code in your vehicle's computer. The code often begins with P0335 or P0336, though the exact number depends on your vehicle's make and model. You can read this code yourself with an inexpensive scanner, or a mechanic can pull it for you.

Key Takeaways

  • A crank sensor failure shows up as a check engine light, rough idle, stalling, or no-start condition, and you can confirm it by reading the trouble code with a scanner.
  • The sensor sits near the crankshaft, usually on the front or side of the engine block, and you can visually inspect it for loose wires or corrosion before testing.
  • A multimeter test measures the sensor's resistance and output voltage, and readings outside the manufacturer's range indicate a failed sensor.
  • Crank sensor replacement typically costs between $150 and $400 in labor and parts, depending on how accessible the sensor is on your vehicle.
  • If your vehicle won't start and you suspect the crank sensor, do not keep cranking the engine repeatedly, as this can damage the starter motor.

Read the diagnostic trouble code first

Before you touch anything under the hood, connect an OBD-II scanner to the diagnostic port under your steering wheel. This port looks like a rectangular connector about the size of a deck of cards. Plug the scanner in, turn the ignition to the "On" position without starting the engine, and follow the scanner's menu to read stored codes.

Codes in the P0335 to P0338 range point directly to the crank sensor or its wiring. Codes like P0016 (camshaft and crankshaft timing misalignment) can also suggest a crank sensor problem, though they sometimes point to other issues. Write down the exact code and any freeze frame data the scanner shows — this tells a mechanic what the engine was doing when the fault occurred.

If you do not own a scanner, most auto parts stores will read the code for free. Call ahead to confirm they offer this service, and bring your vehicle keys so they can connect to your car in the parking lot.

Locate the crank sensor on your engine

The crank sensor sits near the crankshaft, but its exact location varies widely. On many vehicles it bolts to the front of the engine block, near the crankshaft pulley. On others it mounts to the side of the block, close to the oil pan. Some sit inside the distributor or near the transmission bell housing. Check your vehicle's service manual or search online for "[your year, make, model] crank sensor location" to find the right spot.

Once you locate it, look for a cylindrical or rectangular sensor with a wire or connector running to it. Check whether the connector is loose, corroded, or wet. Look for cracks in the sensor body itself. A loose connector or visible corrosion can cause the same symptoms as a failed sensor, and fixing the connection is much cheaper than replacing the part.

Test the sensor with a multimeter

A multimeter is an inexpensive tool that measures electrical resistance and voltage. Set it to the resistance setting (usually marked with the Greek letter omega, Ω) and disconnect the sensor's electrical connector. Probe the sensor's terminals with the multimeter leads and note the resistance reading. Most crank sensors should read between 200 and 900 ohms, though this varies by manufacturer — check your service manual for the correct range for your vehicle.

If the resistance is zero, very high, or outside the expected range, the sensor has likely failed internally. If the resistance is within range, reconnect the connector and set the multimeter to measure DC voltage. Have someone crank the engine while you probe the sensor's output wire (not the ground or power wires). A working sensor should show a voltage that changes as the engine cranks, usually between 0.5 and 5 volts depending on the sensor type.

If the voltage does not change or stays at zero, the sensor is not sending a signal to the computer. This confirms a failed sensor. If you are uncomfortable working with a multimeter, a mechanic can run this test for you in about 15 minutes.

Check the wiring and connector

Before you assume the sensor itself is bad, inspect the wiring harness that connects to it. Look for pinched, cut, or abraded wires. Trace the harness back toward the engine computer and check for loose connections at both ends. Corrosion on the connector pins is common in older vehicles or those exposed to salt spray — you can sometimes clean the pins with a small wire brush or electrical contact cleaner.

Disconnect and reconnect the connector several times to reseat it firmly. Sometimes a loose connection causes the same symptoms as a failed sensor. If the connector is cracked or the pins are bent, you may need to replace just the connector rather than the entire sensor.

What to expect if you replace the sensor

Crank sensor replacement usually takes a mechanic between one and three hours, depending on how accessible the sensor is on your vehicle. Some sensors bolt on from the outside and take 30 minutes; others require removing the timing cover, oil pan, or other components and take much longer. Parts typically cost between $50 and $200, and labor ranges from $100 to $300.

After replacement, the check engine light should turn off within a few driving cycles. If the light returns, the new sensor may be defective, the wiring may still be damaged, or a different fault may be present. Do not ignore a returning check engine light — have the code read again to confirm the problem is solved.

What to do if your car won't start

If your vehicle will not start and you suspect the crank sensor, resist the urge to crank the engine repeatedly. Each cranking cycle drains the battery and can damage the starter motor. Instead, turn the key to the "On" position and listen for a fuel pump hum from the rear of the vehicle. If you hear it, the computer is receiving power, which means the crank sensor failure is preventing the engine from firing rather than preventing the computer from waking up.

Call a tow truck or have the vehicle towed to a mechanic. A no-start condition caused by a crank sensor requires a diagnostic scan to confirm, and you cannot safely drive the vehicle. Do not attempt to push-start or bump-start the engine, as this can damage the transmission and will not work on modern vehicles with automatic transmissions anyway.

Frequently Asked Questions

Can a bad crank sensor cause a misfire?

Yes. A failing crank sensor sends incorrect timing information to the computer, which causes the spark plugs to fire at the wrong moment. This creates a misfire — a cylinder that does not fire or fires late. You may feel a hesitation or stumble during acceleration, or see a flashing check engine light at idle.

Will a crank sensor fail suddenly or gradually?

Usually gradually. You might notice a rough idle for a week, then stalling at stops, then hard starting. Sometimes a sensor fails suddenly after exposure to extreme heat or water, but most give warning signs first. Pay attention to any new rough running or starting trouble and have the code read before the problem gets worse.

Can I drive with a bad crank sensor?

Not safely. A failed crank sensor can cause stalling at any time, including on the highway or at an intersection. The engine may not restart once it stalls. Have the vehicle towed or repaired before driving it again.

What is the difference between a crank sensor and a camshaft sensor?

The crank sensor monitors the crankshaft position, while the camshaft sensor monitors the camshaft position. Both send timing information to the computer, but they measure different parts of the engine. A vehicle has one crank sensor and usually one or two camshaft sensors. Failure of either type causes similar symptoms.

Do I need to clear the trouble code after replacing the sensor?

No. The code will clear automatically after the new sensor runs for several driving cycles without triggering a fault. You can also clear it manually with a scanner, but this is not necessary. If you clear it and it returns, the replacement sensor or wiring is likely defective.