Your car has many different sensors on-board, one of which is the crankshaft position sensor (CKP). Like any other car part, the crankshaft position sensor can eventually fail, and when it does, it can cause a variety of problems.
A faulty CKP sensor can turn on your car’s check engine light, leave you stranded—and more. It’s a problem you’ll want to address right away.
What Does a Crankshaft Position Sensor Do?
The crankshaft is a rotating assembly inside the engine that connects to the pistons and connecting rods. When the engine is running, the linear motion of the pistons causes the crankshaft to turn, thereby creating the rotational force needed to move the vehicle.
As you might guess, the CKP sensor measures the position and speed of the engine’s crankshaft. The sensor creates a signal by reading a toothed or notched wheel that is usually located on the crankshaft or harmonic balancer. For this reason, the crankshaft position sensor’s location is often at the front bottom side of the engine, though, its location can vary from vehicle to vehicle.
The engine computer, which is often referred to as the powertrain control module (PCM), uses the CKP sensor signal when calculating spark timing and (in most cases) fuel injector synchronization. The PCM may also use the CKP signal when managing other functions, such as the variable valve timing system if the vehicle is so equipped. On all vehicles built after 1996, the module also uses the CKP sensor to detect an engine misfire.
Symptoms of a Bad Crankshaft Position Sensor
Because the CKP sensor is a primary input to the PCM, the sensor can cause a range of different problems when it fails. Some of the most common bad crankshaft position sensor symptoms include:
Illuminated Check Engine Light
The PCM monitors the CKP sensor and its circuit. If the module detects a problem, it will turn on the check engine light and store a corresponding diagnostic trouble code (DTC) in its memory.
Engine Refuses to Start
A gas-powered engine needs three primary ingredients to run: spark, an air-fuel mixture, and compression. When the CKP sensor fails, the PCM doesn’t know when to fire the spark plugs and pulse the fuel injectors. As a result, the engine may be starved of fuel and/or spark, resulting in a vehicle that refuses to start.
Hard Starting and/or Stalling
When the CKP sensor is on the fritz, it may produce a weak or erratic signal rather than failing completely. As a result, the vehicle may exhibit hard starting and/or stalling due to improper spark and fuel delivery.
Engine Runs Rough and Misfires
An erratic CKP sensor can cause the PCM to miscalculate fuel injector pulse and spark timing, resulting in an engine that runs rough and misfires. As the driver, you’ll likely interpret the misfire as a subtle shaking or stumble that may intensify when the vehicle is under load. If not corrected, the misfire can cause damage to other parts of the vehicle, such as the catalytic converter.
Reduced Fuel Economy
Obviously, an engine that’s running rough and misfiring (due to a faulty CKP sensor) will experience a reduction in fuel efficiency. A faulty CKP sensor may also prevent fuel-saving equipment, such as the variable valve timing and cylinder deactivation systems, from working properly.
Can You Drive With a Bad Crankshaft Position Sensor?
In many cases, a faulty CKP sensor will prevent the vehicle from starting, which, in turn, will prevent you from being able to drive the car. In such a scenario, you’ll have no choice but to fix the problem right away.
But even intermittent CKP concerns should be addressed immediately, as such issues can lead to stalling and hard starting, making the vehicle unreliable and unsafe.