You are watching: How to reset brake warning light on mercedes
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| W123 dash brake warning lights, a review|
Lets evaluation the W123 brake light warning device. In the dash, there are 2 warning lights linked through the brake device The first and most necessary is the Red " BRAKE " light in the dash. ( photo #1 ). This light has 2 features. It informs you that the parking brake is engaged and also more importantly it informs you that the hydraulic brake device reservoir fluid is at a low level. The device offers a wire schematic that you have the right to see in picture #2. From the #12 fusage, the circuit goes to the warning light in the instrument cluster. From there it travels through cables to both circuits in the brake fluid reservoir and then to ground G102 which is located behind the instrument cluster . The babsence buttons at the height of the reservoir are test buttons for the floats in the reservoir."Reseting" them as is periodically posted, is not rather what you are doing as soon as you press the button. If the light is stuck on and is caused by the float. When you "reset" it you are trying to disattach the float from the lower "on" contacts. This is whats causing the false on indication. The float ( image # 3 ) may be getting old and not move up and also down openly. The older cars have a single chamber mechanism and also just 1 float and also test switch on optimal of the reservoir. Newer models have the dual chamber reservoir and 2 black buttonsThe second circuit of the Red " BRAKE " light goes to the parking brake pedal assembly and also allows you understand when the barking brake pedal is in any position other that totally earlier ( parking brake off ) Picture #4 shows the Service Manual diagram of the switch place. To test the 3 circuits for a fault ( definition your light is on ) you ssuggest disconnect the wire harness going to the reservoir float or parking brake switch one at a time and also examine the light. If the light goes out, then it is that particular circuit. You can replace the parking brake switch but the reservoir switches cannot be reinserted. A brand-new reservoir is required. However the black rubber caps are easily accessible. Of course initially make sure that both reservoir sections are filled with brake liquid to the "MAX" line. To look at the rear chamber it is finest to look on the passenger side of the reservoir in the direction of the ago of the reservoir. I generally wiggle the reservoir side to side, it provides it much easier to watch the liquid level adjust.A second light in the dash is for the FRONT brake pad wear warning system ( picture # 1). As posted, the wear sensors are in the front pads just. 2 wires per wheel, one in each pad. The electrical circuit ( picture #5 ) goes from the #12 fuse, to the instrument cluster power line, with the warning bulb to the 4 sets of sensors. Then to the G102 ground for the left front hand wheel and the G101 ground for the appropriate front wheel. The G101 ground is situated RH front fender behind the headlights. Interestingly sufficient, the wear sensor tells you that your pads are worn out by grounding the circuit ( actually completing the circuit) once the plastic cover of the wear probe sensor is ground ameans and also the exposed probe wire touches the rotor ( that is why it flickers initially ). I actually have actually not checked out the wire for the wear sensor as it goes to either G101 or G102 as displayed in the electric schematic, go number. Tbelow is not a wear warning system for the rear pads or the parking brake shoes. You have to check the rear pads for every 3 front pad replacements ( not a poor concept to examine them every 2 sets of front pads ) The parking prake shoes must last fairly a long time, I personally have actually never before reput a set of parking brake shoes in all the Mercedes I have actually owned (9 at last count). To proccasion from replacing parking brake shoes you need to keep the parking brakes in adjustment and also not drive the vehicle with the parking brake on. I hope this helps anyone that has any type of concerns around the dash brake lights. Dave
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Great article - btw, wright here would certainly I uncover the little babsence plugs that cover the vent/circuit testers - mine are cracked? Fastlane hopefully?