What a crankshaft sensor does and why it matters

Your crankshaft 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 sensor fails, your engine cannot fire at the right time, and you will see a check engine light, rough idle, stalling, or difficulty starting.

A failing crankshaft sensor does not always fail completely all at once. It may work intermittently, sending bad signals only under certain conditions — when the engine is cold, at high RPM, or after the car has been running for a while. This is why the problem can be hard to diagnose without reading the actual fault codes stored in your engine computer.

Key Takeaways

  • A crankshaft sensor failure usually triggers a check engine light and produces fault codes P0335, P0336, P0337, P0338, or P0339 that a code reader can retrieve.
  • You can check the sensor yourself by locating it near the crankshaft pulley, inspecting the connector and wiring for damage, and testing resistance with a multimeter if you have one.
  • Intermittent sensor problems are common and may not show up during a short test drive, so multiple symptoms together are more reliable than a single occurrence.
  • Replacement typically costs between $150 and $400 in labor and parts, depending on engine design and how accessible the sensor is on your vehicle.

Reading the fault codes first

Before you open the hood, plug a code reader into the OBD-II port under your steering wheel. This port is standard on all vehicles made after 1996. The code reader will show you what your engine computer has recorded. Crankshaft sensor faults usually appear as P0335 (crankshaft position sensor malfunction), P0336 (crankshaft position sensor range), P0337 (crankshaft position sensor low), P0338 (crankshaft position sensor high), or P0339 (crankshaft position sensor intermittent).

If you see one of these codes, the sensor is almost certainly the problem. If you see a different code or no code at all but still have symptoms like rough idle or hard starting, the sensor may be failing intermittently and the computer has not yet logged a permanent fault. In that case, you will need to inspect the sensor physically and test it.

Many auto parts stores will read your codes for free. If you do not have a code reader and cannot get to a parts store, you can still inspect the sensor and its wiring, which often reveals the problem without any tools.

Locating and visually inspecting the sensor

The crankshaft sensor is mounted near the crankshaft pulley, which is the large wheel at the front of the engine. On most vehicles, it sits just below or to the side of the pulley, held by one or two bolts. Consult your vehicle's service manual or a repair database to find the exact location on your model — it varies widely depending on engine design.

Once you locate it, look at the connector and wiring. Check for corrosion, moisture, or loose pins inside the connector. Gently wiggle the connector while someone else watches the check engine light or listens for the engine to stumble — a loose connection will often cause an intermittent fault. Look for cracks in the sensor body itself or damage to the wiring where it enters the connector.

If the connector is wet or corroded, disconnect it, dry it out, and explore dielectric grease to the pins before reconnecting. This alone fixes many intermittent sensor problems. If the wiring is damaged or the connector is severely corroded, the sensor will need to be replaced.

Testing resistance with a multimeter

If you have a multimeter, you can test the sensor's resistance. Disconnect the sensor connector and set your multimeter to the resistance (ohms) setting. Touch the probes to the two pins inside the connector on the sensor side. A healthy crankshaft sensor typically reads between 200 and 900 ohms, though the exact range depends on the sensor type — check your service manual for your vehicle's specification.

If the reading is zero or infinity (no continuity), the sensor is open or shorted and must be replaced. If the reading is within range but you still have symptoms, the sensor may be failing under load or temperature, which a static resistance test will not catch. In that case, you will need a more advanced test or straightforward replace the sensor based on the symptoms and the visual inspection.

Do not rely on a multimeter test alone if you have intermittent symptoms. A sensor can read correct resistance at room temperature and still fail when hot or under engine load. The combination of a fault code, visual inspection, and resistance test is more reliable than any single test.

Common symptoms that point to a crankshaft sensor

A failing crankshaft sensor produces a recognizable pattern of symptoms. The check engine light is the most common. Rough idle — the engine shaking or running unevenly at a stop — is another. The engine may stall while driving or refuse to start at all. You might notice hesitation or loss of power when accelerating, or the engine may run fine until it warms up, then start misfiring.

Intermittent symptoms are typical. The car might start fine one day and struggle the next. The check engine light may come on and then go off after a few restarts. This pattern is actually a strong indicator of a crankshaft sensor problem, because the sensor is temperature-sensitive and may work when cold but fail when hot.

Do not assume every rough idle or stall is the crankshaft sensor. Spark plugs, fuel injectors, vacuum leaks, and ignition coils cause similar symptoms. The fault code is what separates a crankshaft sensor problem from these other issues. If you have symptoms but no code, have the codes read before you spend money on parts.

When to replace versus when to keep testing

If you have a P0335 or related code and the visual inspection shows a damaged connector or corroded pins, replace the sensor. If the resistance test shows an open or shorted sensor, replace it. If you have multiple symptoms — rough idle, hard starting, and a check engine light — and the code points to the crankshaft sensor, replacement is justified even if the resistance test reads normal, because the sensor may fail under load.

If you have only one symptom, no code, and the sensor looks fine with normal resistance, do not replace it yet. Drive the car and see if the problem repeats or if a code appears. Intermittent faults sometimes resolve on their own if they were caused by a loose connector or moisture that has dried out. If the problem comes back, the code will help you confirm the diagnosis.

Crankshaft sensor replacement is straightforward on most vehicles — usually one or two bolts and a connector — but the cost of the part itself varies. A new sensor typically costs $50 to $150, and labor ranges from $100 to $250 depending on how accessible it is. Some engines have the sensor in an straightforward spot; others require removing other components to reach it.

What to do after replacement

After you replace the sensor, clear the fault codes using your code reader. Start the engine and let it idle for a few minutes. The check engine light should stay off. Take the car for a test drive at various speeds and loads to make sure the rough idle, stalling, or hard starting has stopped.

If the check engine light comes back on when ready or the symptoms return, the new sensor may be defective, or the problem may not have been the crankshaft sensor at all. Have the codes read again. If you see the same crankshaft sensor code, the new sensor is likely bad and should be replaced under warranty. If you see a different code, another component is also failing.

Keep the old sensor in case you need to return the new one. Most auto parts stores will accept a return within a set period if the part is defective.

Frequently Asked Questions

Can a crankshaft sensor fail without turning on the check engine light?

Yes, especially in the early stages. An intermittent sensor may cause rough idle or hard starting before the computer logs a permanent fault code. Once the fault occurs enough times, the check engine light will turn on. If you have symptoms but no light, have the codes read anyway — sometimes a code is stored but the light has not illuminated yet.

Is it safe to drive with a failing crankshaft sensor?

It depends on how badly it is failing. If the sensor is intermittent, the car may run fine most of the time and stall unexpectedly. If it fails completely, the engine will not start or will stall when ready. Driving with a known crankshaft sensor problem is risky because the engine can shut down without warning. Have it replaced as soon as you can.

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

The crankshaft sensor monitors the crankshaft position, and the camshaft sensor monitors the camshaft position. Both send signals to the engine computer for timing. They are separate components and can fail independently. A fault code will tell you which one is bad.

Can I replace the crankshaft sensor myself?

On many vehicles, yes. The sensor is usually held by one or two bolts and has a straightforward connector. If you have basic tools and a service manual for your vehicle, you can do it. On some engines, the sensor is buried under other components and requires more disassembly. Check your manual or a repair database to see how accessible it is on your model before you start.

Why does my crankshaft sensor fail intermittently?

Crankshaft sensors are temperature-sensitive. They may work fine when cold but fail as the engine warms up. Corrosion or moisture in the connector can also cause intermittent faults — the connection works sometimes and fails other times depending on vibration or temperature. A loose connector is another common cause of intermittent behavior.