2009 C63 "Check Brake Fluid Level" message
11-24-2016, 05:54 PM
#1
Junior Member
Thread Starter
2009 C63 "Check Brake Fluid Level" message
I continue to get a check brake fluid level warning message but my fluid is at the max line. I've read a few posts online, and I'm getting mixed information as to what could be causing it. I've read that the sensor is normally open. It will close the circuit if the level gets low. If I understand this correctly, unplugging the sensor at the reservoir would open the circuit and prevent the error from being detected. I'm not sure I agree with the normally open theory. If I unplug the sensor, the message remains. Another thing is that the red "brake" light comes and goes with what seems to be inclines and declines, which would potentially lead a driver to believe the fluid level is near the low mark causing it to constantly change the level being sensed. Do I just conclude I have a bad sensor and replace the reservoir? Is there a way for me to test to determine if the sensor is faulty before I dive into a reservoir replacement and fluid change? Thanks in advance for any help you can provide.
08-19-2017, 08:52 PM
#2
Newbie
Brake Fluid Level
I also have an 09 C300 Sport with 10K miles and have the same problem today. Check brake fluid level and it shows max level but brake light stays on. Any help greatly appreciated.
08-19-2017, 11:17 PM
#3
MBWorld Fanatic!
I continue to get a check brake fluid level warning message but my fluid is at the max line. I've read a few posts online, and I'm getting mixed information as to what could be causing it. I've read that the sensor is normally open. It will close the circuit if the level gets low. If I understand this correctly, unplugging the sensor at the reservoir would open the circuit and prevent the error from being detected. I'm not sure I agree with the normally open theory. If I unplug the sensor, the message remains. Another thing is that the red "brake" light comes and goes with what seems to be inclines and declines, which would potentially lead a driver to believe the fluid level is near the low mark causing it to constantly change the level being sensed. Do I just conclude I have a bad sensor and replace the reservoir? Is there a way for me to test to determine if the sensor is faulty before I dive into a reservoir replacement and fluid change? Thanks in advance for any help you can provide.
These things as I recall use a reed switch hermetically sealed to keep them dry from fluid water etc.
They are normally closed in this application. The system sees the sensor this way because there is current flow in the electronic testing for its presence. If you disconnect it there is no signal to the system and rather than dealing with low fluid it dealing with a critical piece of equipment in the system that has gone missing.
I suspect if you put a jumper across the contacts may bet is you will lose both fault signals but if you do this put a 0.5 amp fuse in the wire just so you don't fry something.
There will be a float of some kind in the master cylinder which has a magnet attached. As it fluid level drops at some preset level the flux of the magnet is sufficient to open the reed switch and this creates the low level alert.
So you could have a bad float that is stuck or the sensor itself is fried.
I suspect there is a code somewhere to differentiate the issues. It is probable as well the code will be stored and have to be cleared.
08-21-2017, 10:26 AM
#4
Super Member
Ok so you are challenging the old brain.
These things as I recall use a reed switch hermetically sealed to keep them dry from fluid water etc.
They are normally closed in this application. The system sees the sensor this way because there is current flow in the electronic testing for its presence. If you disconnect it there is no signal to the system and rather than dealing with low fluid it dealing with a critical piece of equipment in the system that has gone missing.
I suspect if you put a jumper across the contacts may bet is you will lose both fault signals but if you do this put a 0.5 amp fuse in the wire just so you don't fry something.
There will be a float of some kind in the master cylinder which has a magnet attached. As it fluid level drops at some preset level the flux of the magnet is sufficient to open the reed switch and this creates the low level alert.
So you could have a bad float that is stuck or the sensor itself is fried.
I suspect there is a code somewhere to differentiate the issues. It is probable as well the code will be stored and have to be cleared.
These things as I recall use a reed switch hermetically sealed to keep them dry from fluid water etc.
They are normally closed in this application. The system sees the sensor this way because there is current flow in the electronic testing for its presence. If you disconnect it there is no signal to the system and rather than dealing with low fluid it dealing with a critical piece of equipment in the system that has gone missing.
I suspect if you put a jumper across the contacts may bet is you will lose both fault signals but if you do this put a 0.5 amp fuse in the wire just so you don't fry something.
There will be a float of some kind in the master cylinder which has a magnet attached. As it fluid level drops at some preset level the flux of the magnet is sufficient to open the reed switch and this creates the low level alert.
So you could have a bad float that is stuck or the sensor itself is fried.
I suspect there is a code somewhere to differentiate the issues. It is probable as well the code will be stored and have to be cleared.
Jim G
08-21-2017, 10:46 AM
#5
Member
I've had this message pop up a couple of times on my '09 as well. I check the fluid and then go through the menu to say 'OK' and the message goes away for quite a while. So yeah, faulty sensor or something.
08-21-2017, 10:56 AM
#6
MBWorld Fanatic!
For example, try running without TPMS sensors in your wheels and you will get a fault alarm and no you cannot shut the system off. I already checked. So if you want to run a set of wheels without them that alarm will be in your face constantly.
The systems go through a self check everytime you start the car. All those pretty lights that come on when you turn the key to the first stop or push the button go out because everything is OK in the system. They stay on because the system has detected a fault before it even begins to monitor,
