Troubleshooting BMW E90 N51 Crankshaft Position Sensor & Idle Issues
How to Truly Test if Your BMW N51 Crankshaft Sensor is Bad: A Simple Guide for Everyone
If you drive a BMW E90 with the N51 engine, you might have heard about the crankshaft position sensor and how important it is for your car to run properly. But what happens if the sensor stops working and affects the valve timing? In this guide, you will learn how to Truly test if your BMW N51 crankshaft sensor is functioning correctly by monitoring the RPM and comparing it to the expected sensor signal. is bad, and we will explain everything step by step. Don’t worry, a BMW mechanic can assist you if needed! You don’t need to be an expert to follow along—this guide is written in easy language, perfect for beginners and even 6th graders.
By the end of this guide, you will understand what the crankshaft position sensor does, why it’s so important, and how to test it yourself with some simple tools, including checking the MAF sensor and the ignition system. You can also check out my other blogs for more car-related insights, like how to ensure your car lift arm height is right for precision and safety in your garage setup, especially when working on a 2007 328xi. here.
What is a Crankshaft Sensor, and Why is it Important?
Let’s start by learning what a crankshaft sensor does. The crankshaft sensor in your BMW N51 engine is like the engine’s helper. It watches how fast the engine spins and tells the car’s computer what’s going on with the manifold and cylinder performance, which is crucial for the N51 rough idle. The car’s computer then uses this information to make sure the engine runs at the right speed and with the correct timing.
If the crankshaft sensor isn’t working properly, the engine in your 2011 BMW might not start, or it could stall while you’re driving. You could even experience other problems, like the engine making strange noises or the car not speeding up the way it should, possibly due to a faulty intake manifold gasket or fuel pressure issues. So, it’s important to know how to test the crankshaft position sensor and ensure the valve cover is secure. Truly test if your BMW N51 crankshaft sensor is functioning correctly to avoid issues during a cold start. is working or not. If you’re having similar issues with other cars, like diagnosing brake light problems fast in a 2011 Toyota 4Runner, you might find this blog post helpful.
Common Signs of a Bad Crankshaft Sensor
Before we get into how to test the sensor, let’s talk about the signs that show the crankshaft sensor might be bad. Here are some common symptoms to look out for:
- Engine stalls can often be traced back to issues with the crankshaft position sensor or the valve timing.: If your car suddenly shuts off while you’re driving, the crankshaft sensor might be the reason.
- Trouble starting: If your car takes a long time to start, it could be because the sensor isn’t sending the right signals.
- Poor acceleration can be a sign of a faulty crankshaft sensor or issues with the intake manifold, which can affect the sensor signal.: Is your car slower than usual when you press on the gas? The crankshaft sensor might not be giving the engine the information it needs, affecting the throttle response and causing issues similar to those seen in the 2006 BMW 325i.
- Check engine lightIf the warning light comes on, the car might be telling you there’s a problem with the camshaft sensor.
- Rough idling can indicate issues with the N51 rough crankshaft position sensor.: If the car feels shaky when it’s just sitting still, the crank sensor could be acting up.
When you notice these problems with the engine or the crankshaft sensor, it’s a good idea to consult a mechanic. truly test if your BMW N51 crankshaft sensor is working properly. Let’s learn how to do that next in the context of a BMW X3.
How to Test if Your BMW N51 Crankshaft Sensor is Bad
Testing the crankshaft sensor might sound hard, but with the steps below, you’ll be able to do it easily and check the RPM readings. Just follow along!
Step 1: Use an OBD-II Scanner
The first way to test if your crankshaft position sensor BMW is bad is to use an OBD-II scanner. This is a device that can read the error codes in your car’s computer, including those for the cam sensor.
What you need: A reliable scanner to read the error codes from the position sensor on BMW models. tools to check the crankshaft position sensor and the ignition system. a multimeter and a crankshaft position sensor diagnostic tool, which can be discussed further on a BMW forum.
- OBD-II scanner (You can buy one online or borrow one from an auto parts store.)
How to do it with your BMW E90 E91 E92 E93:
Start by inspecting the throttle and checking for any issues with the crankshaft sensor.
- Plug the scanner into the OBD-II port in your BMW N51. You’ll find the port under the dashboard, usually near the driver’s seat, where you can connect the diagnostic tool for the crankshaft position sensor.
- Turn the key to the “on” position but don’t start the engine.
- The scanner will read any error codes from your car, including those related to the eccentric shaft sensor. Look for codes like P0335 or P0336. These codes mean the crankshaft position sensor might be having trouble and could affect the DME.
If you see these codes, it’s a good sign that the crankshaft sensor could be bad and needs more testing.
Step 2: Check the Sensor and Wires for Damage
Before you use any other tools, it’s a good idea to just look at the crankshaft sensor and its wires, as well as the valve cover for any leaks, which could lead to a fault code. Sometimes the problem is not with the sensor but with the wires or connectors.
What to look for in the crankshaft position sensor and its relation to the valve timing:
- Are the wires broken or damaged?
- Are the connectors loose or dirty on the camshaft sensor in your BMW?
- Is there oil or dirt covering the sensor?
If you find anything wrong, you should clean or fix the wires and connectors related to the crankshaft position sensor first to prevent it from going bad. Sometimes, that’s all it takes to fix the problem. But if everything looks fine, you’ll need to move on to the next step.
Step 3: Test the Voltage with a Multimeter
A multimeter is a tool that can measure the electricity in your car’s wires. You can use it to see if the crankshaft sensor is getting the right amount of power from the battery and the coil.
What you need:
- A digital multimeter is essential for diagnosing issues with the camshaft sensor in your BMW.
How to do it: Check the sensor signal to ensure proper functionality.

- First, disconnect the crankshaft sensor from the car’s wiring.
- Set your multimeter to measure voltage.
- Turn the key to the “on” position without starting the engine.
- Use the multimeter to check the voltage at the sensor’s connector. You should see about 5 volts at the ignition system.
If you don’t see the right amount of voltage from the crankshaft position sensor, it might not be working, or there could be a problem with the wires leading to the eccentric shaft sensor.
Step 4: Test the Sensor’s Resistance
Next, you can test the resistance of the sensor. This will help you see if the crank position sensor itself is broken.
What you need:
How to do it:
- Set the multimeter to measure resistance (ohms) to test the camshaft position sensor.
- Touch the ends of the multimeter to the two terminals of the camshaft position sensor.
- Look at the reading on the multimeter and compare it to the resistance range in your BMW N51’s manual. Normally, the resistance should be between 500 and 900 ohms for the crankshaft position sensor to ensure proper cylinder timing.
If the reading is much higher or lower, then the crankshaft sensor is probably bad and needs to be replaced.
Step 5: Use an Oscilloscope for More Accurate Testing
If you want to be extra sure, you can use an oscilloscope to see the signal the crank position sensor is sending. This tool shows the sensor’s signal in real-time as a wave on the screen.

What you need:
- An oscilloscope
How to do it:
- Connect the oscilloscope to the crankshaft position sensor to check its output.
- Start the engine and watch the screen for any signs of misfire or abnormal RPM.
- A good crankshaft sensor will show a smooth wave pattern.
If the signal from the crankshaft position sensor looks erratic or broken, then it is not working properly.
When Should You Replace the BMW N51 Crankshaft Sensor?
After testing, if you find that the crankshaft position sensor is not working, it’s time to replace my crankshaft position sensor. The good news is that replacing the sensor is not too hard. You can do it yourself with a few tools, including a multimeter to test the sensor signal.
What you need:
- New crankshaft sensor (make sure it’s the right one for your BMW N51)
- Socket wrench set is essential for replacing components like the crankshaft sensor or spark plug.
- Screwdriver
How to replace the sensor:
- First, disconnect the car’s battery to make sure it’s safe to work on the car.
- Find the crankshaft sensor in your BMW N51 engine. (Check your car’s manual if you don’t know where the crankshaft position sensor is.)
- Disconnect the sensor from the wires and remove any bolts holding it in place.
- Take out the old sensor and put in the new OEM one for optimal performance.
- Reconnect the wires and tighten the bolts.
- Reconnect the car’s battery and start the engine.
After you replace the sensor, clear the error codes from the car’s computer using the OBD-II scanner and make sure everything is working right. For more tips on keeping your vehicle in top shape, you can also check my article on car DVD systems, comparing Leespring and Xtron models here.
Extra Tips to Keep Your BMW N51 Running Well
Now that you know how to truly test if your BMW N51 crankshaft sensor If the crankshaft position sensor is working, here are a few tips to help you keep your car in good shape, including checking the manifold.
- Regular maintenance of the crankshaft position sensor is essential for optimal performance, especially in a BMW X3.: Make sure to follow your car’s maintenance schedule to catch problems early.
- Check for dirt and debris: Dirt can cause sensors to fail, so make sure the sensor and its wires are clean.
- Test the battery and also inspect the coil for any signs of wear.Sometimes, a weak battery can cause sensors, including the eccentric shaft sensor, to stop working properly.
- Stay alertIf you notice any strange symptoms like rough idling or the check engine light coming on, test your crankshaft sensor early to avoid bigger problems like misfires, which can also be related to the cam sensor.
Want to know more about older vehicles, like if a 2002 Toyota 4Runner has a crankshaft position sensor or how it compares to the 2006 BMW 325i? Check out my detailed post here.
Conclusion: Keep Your BMW N51 Running Smoothly
The crankshaft sensor is a small but important part of your BMW N51 engine. It helps keep the engine running smoothly and tells the car’s computer how fast the engine is spinning, which is crucial for the vanos system. If you notice signs like stalling, hard starts, or the check engine light turning on, it’s important to check the spark plug and crankshaft sensor. truly test if your BMW N51 crankshaft sensor is working correctly.
By following the steps in this guide—using an OBD-II scanner, checking the wires, testing the voltage and resistance of the crank sensor—you can easily find out if the sensor is bad. If it is, replacing the sensor is a simple job that you can do at home on your BMW 3 series. Once you’ve tested or replaced the crankshaft position sensor, your BMW 328i N51 will run like new again, just like it did when the camshaft and vanos system were functioning well.
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