How to Diagnose Eccentric Shaft Sensor Issues in BMW?

BMW’s eccentric shaft sensor… a component so tiny that it often goes unnoticed during routine engine maintenance work. But guess what??? This trivial-looking element, if malfunctions, can have a profound impact on the way your engine operates.

Today’s blog post uncovers some interesting facts about this mysterious component… facts you won’t find anywhere but here.

Eccentric Shaft Sensor: Why It Matters

Before we explain what an eccentric shaft sensor is and how useful it is for your BMW engine, it is important that you have a basic understanding of what Variable Nockenwellensteuerung is :):):)

Don’t get confused by this fancy word… it is German for variable camshaft timing (VANOS in short). It serves an important purpose in your BMW.

What’s that, you’re probably wondering? Well, it adjusts the timing of intake and exhaust valves by mechanical/hydraulic means to optimize the engine’s overall efficiency. Neither a very difficult task… nor an easy one.

To be able to do its job with utmost precision, VANOS relies on real-time inputs from a bunch of sensors… including the one this topic is about. Yes, we are talking about the ‘Eccentric Shaft Sensor’.

This sensor helps the VANOS keep track of the position of your BMW engine’s eccentric shaft (which also goes by the name ‘the camshaft’) on a real-time basis.

The eccentric shaft sensor is essentially…

- A small cylindrical component

- Bolted to the timing system

- Integral to BMW 1 Series, 3 Series, and 5 Series models

Why It Might Malfunction

Some of the leading reasons why your vehicle’s eccentric shaft sensor might abruptly cease functioning are as follows:

#1- Not sticking to the engine’s routine maintenance schedule is one reason why your BMW’s eccentric shaft sensor may fail prematurely.

#2- Not changing the oil at the recommended interval, not replacing a damaged valve cover gasket on time are among the issues that can result in untimely wear of the eccentric shaft sensor.

#3- The sensor won’t be able to send accurate readings to the VANOS mechanism if there is something off with its circuit… such as a frayed wire or a blown fuse.

#4- If the sensor gets contaminated with oil because of deformities in the valve cover, its ability to keep track of eccentric shaft’s movement will be impacted.

#5- Manufacturing defects may also cause the eccentric shaft sensor of your BMW to fail early.

Signs Your BMW Eccentric Shaft Sensor Is Faulty

The eccentric shaft sensor your BMW comes equipped with is not something that fails very often… but when it does malfunction, you might notice one or more of the following signs.

#1- Irregular idle

A glitch in eccentric shaft sensor can throw your BMW’s engine timing out of sync. This disruption can result in all sorts of drivability issues… ranging from ‘Fluctuating idle RPMs’ to engine misfire.

#2- Engine's efficiency has declined

The VANOS system… the mechanism responsible for optimizing the timing of valve lift event rely on real-time inputs from the eccentric shaft sensor. If the sensor gives up, the engine’s performance will suffer.

#3- Reduced fuel efficiency

Your BMW engine is likely to consume more fuel than usual if its timing is off… either because of a faulty eccentric shaft sensor or some other reason.

#4- Unusual engine noises

Has your BMW engine been giving off unusual ticking or knocking noises lately? It could be due to the fact that the defective eccentric shaft sensor has destabilized the valve-train operation.

So, The Diagnosis Process

If you’re suspecting a glitch in your BMW’s eccentric shaft sensor, confirm it with the following diagnostic steps:

#1- Plug an OBD-II scanner into your BMW’s diagnostic port and scan for trouble codes stored in the fault memory. Look for error codes like 2A87, 2A88, etc.

#2- You can simply check for visible damage marks on the sensor. Look for oil leaks around the sensor and check for physical wear or corrosion.

#3- Use a multimeter to examine the sensor's resistance. Compare the readings with that mentioned in the service manual.

#4- Check the sensor circuit for signs of short circuits, loose connections, etc.

Wrapping Up

If you want your BMW’s VANOS system to function with utmost precision, ensure the upkeep of its eccentric shaft sensor. Have its functionality tested every now and then at a reputed European auto service center, and consider replacing it if it appears to have defects.