Mercedes-Benz SL550 Crankshaft Position Sensor

What is a crankshaft position sensor in a car?

Just like many other sensors in your car, the crankshaft position sensor is there to help you drive safely and smoothly. A crankshaft position sensor is used to detect the speed and position of the crankshaft in the engine. A crankshaft is a rotating assembly in the engine that is connected to the connecting rods and the pistons. When the engine runs, the linear motion of the pistons rotates the crankshaft, creating the torque needed to move the car. The crankshaft sensor is usually located on the lower front end of the engine. It reads a toothed or notched wheel that is commonly found on the crankshaft or harmonic balancer and generates a signal to the powertrain control module (PCM). The PCM (also known as engine computer) uses the signals from the crankshaft position sensor to calculate the spark timing and fuel injector synchronization. The powertrain control module can also use the signal from the crankshaft position sensor to manage other functions like variable valve timing. PCM can also use this sensor to detect an engine misfire.

Camshaft position sensor failure symptoms

• Check engine light: Since the powertrain control uses the data from the crankshaft position sensor to regulate the spark timing and air-fuel ratio, it will turn on the check engine light if it thinks there is something wrong with the crankshaft position sensor.
• Engine start failure: An engine needs a combination of ignition, air-fuel mixture, and compression to function. When the crankshaft position sensor fails, the engine computer does not know when to send in the fuel or when to ignite the spark plugs, thus the engine will fail to start.
• Engine misfire: Without a well-functioned crankshaft position sensor, the powertrain control module can not know when is the good time to ignite the spark plugs, or how much fuel the engine currently needs. As a result, you can feel your engine run rough and misfire. It is common that drivers don’t blame the subtle shaking on the engine, and let the damages enlarge over time.
• Decrease in MPG: If the engine can’t run well, its fuel efficiency will suffer. Fuel-saving equipment like the cylinder deactivation system and the variable valve will suffer if the engine can’t work properly due to the failure of a crankshaft position sensor.

Can you drive with a bad crankshaft position sensor?

Usually, if your car realizes the crankshaft position sensor is broken, it will refuse to start before you get the problem solved. But just in case the engine computer didn’t make the right decision, we still recommend you not to drive your car if you know the crankshaft position sensor is broken. A broken crankshaft position sensor can cause the car to stall or have a hard start. Can you imagine your car doing this while you are driving on the highway? If we ignore a broken crankshaft position sensor, the damage it can cause might be a lot higher than the cost to replace it.

Why crankshaft position sensor go bad?

• Engine overheating: The engine can get very hot while it is working. The crankshaft position sensor can handle the heat, normally. But if the engine gets overheated, it can be too hot for the sensor to handle. In this case, the plastic casing that protects the sensor can melt, and the components inside can get damaged.
• Wiring harness problem: Yes, it can be a wiring harness problem again. Wiring harnesses are a common reason that an electric part malfunctions. Check if the connection is loose or the harness material is aged. An untreated wiring harness problem could lead to bigger issues over time.
• Faulty wheel and pin: A crankshaft position sensor works by detecting the toothed or notched wheel that is commonly found on the crankshaft or harmonic balancer. If the wheel gets damaged, the sensor can’t pick up a correct pulse pattern, and thereby it can’t pass the correct information to the engine computer.

How to replace the crankshaft position sensor?

The best way to fix this problem is to go to a professional mechan ic. But if you are experienced in repairing jobs, it is feasible to change or replace a crankshaft position sensor by yourself.

First, you want to make sure your car battery is disconnected before all your operations. This is to protect you and your car as well. Then you can use the owner’s manual of your car to find out where the crankshaft position sensor is. Now you find the sensor, disconnect all the wire harnesses before you remove them. We recommend you take a photo of how the wires are attached. You might need that later. Next, you can remove the bolts and the sensor, and replace a new one. Make sure you replace a new O-ring. Then you do the same things as earlier but in the opposite order.