Crankshaft Position Sensor: What It Does, Symptoms, Location, and Replacement Cost
Learn what a crankshaft position sensor does, common symptoms of failure, where it is located, and what replacement costs. Includes how it differs from the camshaft position sensor.
The crankshaft position sensor is one of those small components that has an outsized effect on whether your car starts and runs properly. Most drivers have never heard of it until something goes wrong, and by then the symptoms can be alarming enough to make you think the problem is far worse than it actually is. This guide covers what the crankshaft position sensor does, how to recognize when it is failing, where to find it on your vehicle, and what replacement involves.
What Does a Crankshaft Position Sensor Do?
The crankshaft position sensor monitors the position and rotational speed of the crankshaft and sends that data to the engine control module (ECM), also called the engine control unit (ECU). The ECM uses this information to determine the precise timing for fuel injection and ignition spark.
Without accurate crankshaft position data, the engine cannot time these events correctly. The result is misfires, rough running, or the engine refusing to start at all.
The sensor works by detecting notches or teeth on a reluctor ring (also called a tone ring) attached to the crankshaft. As the crankshaft rotates, the sensor reads these teeth and generates a signal that tells the ECM exactly where each piston is in its cycle at any given moment.
Crankshaft Position Sensor vs. Camshaft Position Sensor
These two sensors are related but distinct. A common point of confusion is mixing up the crankshaft position sensor with the camshaft position sensor.
- Crankshaft position sensor: Tracks crankshaft rotation and piston position. Used for ignition timing and fuel injection.
- Camshaft position sensor: Tracks the camshaft’s position relative to the crankshaft. Used primarily to determine which cylinder is on its compression stroke, which helps the ECM manage sequential fuel injection.
Both sensors work together. If either one fails, the ECM loses critical timing data. In many cases, the engine will run poorly or not at all. Diagnostic trouble codes (DTCs) from an OBD-II scanner help distinguish which sensor has failed.
Crankshaft Position Sensor Symptoms
Recognizing crankshaft position sensor symptoms early can prevent being stranded. Here are the most common signs:
- Engine misfires. The engine fires at the wrong time or skips firing entirely. You may feel a stumble or hesitation, especially under acceleration.
- Hard starting or no start. If the ECM has no crankshaft position data, it may refuse to fire the injectors or spark plugs at all. The engine cranks but does not start.
- Rough idle. The engine may shake or run unevenly while sitting still.
- Check engine light. Codes P0335, P0336, P0337, P0338, and P0339 all relate to crankshaft position sensor circuit issues.
- Engine stalls. The car may run fine for a while and then cut out unexpectedly, particularly when the engine is warm. This is a classic sign of a sensor that works when cold but fails as it heats up.
- Poor fuel economy. Incorrect timing affects combustion efficiency, which increases fuel consumption.
If you see a check engine light and any of these symptoms together, the crankshaft position sensor is a strong candidate.
Crankshaft Position Sensor Location
The crankshaft position sensor location varies by vehicle make and model, but it is always near the crankshaft. Common mounting locations include:
- Near the harmonic balancer (front of the engine, behind the crankshaft pulley)
- On the engine block near the bottom, facing the reluctor ring on the flywheel or flexplate
- Near the transmission bell housing on rear-wheel-drive vehicles
On most vehicles, the sensor is a small cylindrical or rectangular component with a single electrical connector. It is usually held in place by one or two bolts.
The best way to confirm the exact location for your specific vehicle is to check the factory service manual or use an online resource like AllData or Mitchell1 with your VIN. The location matters because accessibility affects how long the replacement takes and therefore the labor cost.
Crankshaft Position Sensor Replacement
Replacing a crankshaft position sensor is often a straightforward job. On accessible locations like the front of the engine near the harmonic balancer, a competent DIY mechanic can do it in 30 to 60 minutes with basic tools.
General replacement steps:
- Disconnect the battery negative terminal.
- Locate the sensor and unplug the electrical connector.
- Remove the retaining bolt or bolts.
- Pull the old sensor out and note the depth it was seated.
- Insert the new sensor to the same depth and tighten the bolt to spec.
- Reconnect the electrical connector and battery.
- Clear the trouble codes with an OBD-II scanner and test drive.
Replacement cost:
- Part cost: $20 to $100 depending on the brand and vehicle
- Labor cost: $50 to $200 depending on accessibility and shop rates
- Total: $70 to $300 in most cases
Some vehicles place the sensor in a difficult location that requires removing other components to access. On those vehicles, labor costs rise significantly.
After replacement, the ECM on some vehicles requires a crankshaft relearn procedure using a scan tool to recalibrate timing. Not all vehicles need this, but it is worth checking before driving after the replacement is complete.
Should You Drive with a Bad Crankshaft Position Sensor?
The short answer is no, not if you can avoid it. A failing sensor can cause the engine to stall without warning, which is a safety risk in traffic. If the sensor fails completely, the vehicle will not start at all.
If the sensor is intermittently failing (the car sometimes starts and sometimes does not, or stalls occasionally), get it diagnosed and replaced before it leaves you stranded.
The Short Answer
The crankshaft position sensor monitors crankshaft speed and position to help the ECM time fuel injection and ignition. When it fails, expect misfires, hard starting, rough idle, stalling, and a check engine light with codes in the P033x range. The crankshaft position sensor location is always near the crankshaft, typically at the front of the engine or near the flywheel. Replacement is usually straightforward and costs $70 to $300 total. Do not confuse it with the camshaft position sensor, which is a related but separate component. If you suspect either one, an OBD-II scan is the first step.
