DISCLAIMER: THIS IS FOR INFORMATIONAL PURPOSES ONLY. Any attempt to modify your vehicle is done at your own risk. You risk your life or at the very least causing damage to your vehicle or vehicle electronics which will be expensive to repair! If you do not regularly inspect your brakes you won’t know your pads are low or gone, leading to rotor damage, inability to stop the car and possible death or death of others when you crash!
What is a Brake Wear Sensor?
The Brake Wear Sensor on the BMW’s are a small plastic device with 2 wires at the harness end. The wire’s are connected together at the sensor end inside the plastic creating a closed circuit. The sensor itself is designed in a way that when installed with new set of pads it is set in a grove in the center of the pad relatively far from the face of the rotor.
As your brake pads wear down the sensor plastic housing begins to make contact with the rotor and it too begins to wear away along with the brake pad. Until the pad and sensor housing are low enough that the wire inside the sensor is exposed and then “cut” by the friction of continued wear. This breaks the close circuit and triggers the low brake pad warning light on your dash board. It’s really that simple, there is no fancy electronics involved here just essentially a switch that is “turned off” by the fact that the wire is broken when the pads are low enough.
How does the bypass work?
Easy, simply cut off the sensor from the end of the harness, strip back a little bit of each of the 2 wires on the harness that is still connected to the car and twist them together, wrap with electrical tape or heat shrink to prevent moisture from corroding the exposed wires and secure the wire in place so that it is not dangling loose where it may get caught the rotor, brake assembly, wheels or road debris.
This makes the car think the sensor is still intact, forever. It will NEVER trigger the warning light even if you had no brakes on the car at all.
Why bypass the sensor?
Because it add’s extra cost to replacing brakes and in my case when making this video the car has a lot of other issues where I believe the new brakes are going to last longer than the engine, so I’m not concerned. I also regularly work on the car trying to keep it alive so I inspect the brakes among other parts often which is important if anyone was to do this modification!
At a price of $25 for a genuine sensor that seems like a high price when you pair it with the average cost of a set of pads around $30.
Secondly, in my specific case the sensor was still actually good it had not been ground down far enough to actually break the wire and trip yet but the brake light had come on in the car anyway. As you saw in the video, one of the lead wires to the sensor is what actually broke, which has the same effect of the sensor itself being ground down, the circuit is broken and the car thinks the pads are too low. If you try to use every bit of pad surface before changing brakes you will always have to replace your sensor. But if you change the pads early, your sensor will be well worn down like mine was but still not tripped yet making it 100% reusable with the new pads you install.
This means you MUST manually inspect your brakes on a regular basis to ensure YOU catch when the brakes are low since the car will no longer warn you. For a decades cars did not have electronic wear sensors, pad’s just had a metal fin that would scrape along your rotor when the pads were low enough to reach the fin, creating a squeal that was loud enough for most people to hear. You (or your mechanic) regularly checked the brakes typically with every oil change.
If you ignore your pad’s, they will eventually completely wear away leaving the metal backing plate smashing down against the rotor which will not only completely destroy the rotor but will also most likely not let you stop the car at all which could lead to you killing yourself or someone else.