Front Brake Warning

[mr.fabulous]

I posted about this yesterday in the Suspension|Brakes|Chassis forum... but I now have extra information and so I thought I'd ask here.

My car is showing a red front pads service indicator. If I try to reset the thing using the controls at the end of the turn signal stalk, I get to the little spinning clock while holding the BC button... but the thing fails to reset. I am able to reset/adjust other indicators with this method, but the front pads won't change. If I connect my BT Scan Tool and do a Condition Based Reset, I get basically the same results (the tool errors trying to reset the front pad indicator, saying something about not being able to talk to the controller).

I did this several times yesterday and now both the front and rear pad service indicators are yellow (not amber) and the miles remaining is just blank underscores ______.

I have a red car-on-a-lift warning and the BRAKE lamp is lit. The owner's manual suggests this means the front pads are worn. I did my brakes a few weeks ago and in the process broke the front wear sensor. I don't feel like I need that and so I cut the end and secured the remaining lead to the strut with a tie wrap.

So the car is telling me the wear sensor has triggered (it has not) and the service indicators for pad wear remaining are all wonky. Any thoughts will help.

[Mr Rooty Von Tooty]

What's wonky is you broke the front wear sensor and didn't fix it.

[Matticus91]

Originally Posted by Mr Rooty Von Tooty

What's wonky is you broke the front wear sensor and didn't fix it.

Yeah that's pretty much it... I don't know how you thought this wouldn't cause warning lights.

[mr.fabulous]

Originally Posted by Matticus91

Yeah that's pretty much it... I don't know how you thought this wouldn't cause warning lights.

Brake wear sensors trigger when the sensor finds ground (rotor). What's wrong with leaving it out? Been this way since January.

[Ric in RVA]

Originally Posted by mr.fabulous

Brake wear sensors trigger when the sensor finds ground (rotor). What's wrong with leaving it out? Been this way since January.

You have it backwards.

Brake wear sensor are two stage and trigger when a wire is cut.

First stage wears through and it leaves stage 2 intact. Stage 2 has a resistor so computer can see only stage 2 remains.

Stage 2 wears away and circuit resistance goes to infinity and computer knows brakes are worn out.

Take you brake sensor. Solder the wires together, tape up and reinstall.

Reset and computer should see an "intact" brake sensor.

[mr.fabulous]

Originally Posted by Ric in RVA

You have it backwards.

Brake wear sensor are two stage and trigger when a wire is cut.

First stage wears through and it leaves stage 2 intact. Stage 2 has a resistor so computer can see only stage 2 remains.

Stage 2 wears away and circuit resistance goes to infinity and computer knows brakes are worn out.

Take you brake sensor. Solder the wires together, tape up and reinstall.

Reset and computer should see an "intact" brake sensor.

Strange it took the car three months to see the thing was missing (cut). I'll install a new one, grrrrr.

Thanks for the help

[Ric in RVA]

Originally Posted by mr.fabulous

Strange it took the car three months to see the thing was missing (cut). I'll install a new one, grrrrr.

Thanks for the help

My guess is that some wires were touching where it was cut thus making the system think the sensor was intact. As it corroded the continuity failed and the warning started.

[jlc45]

Hey Ric. Are you sure your explanation is correct? Wouldn't the resistance be "infinity" if the wire is cut? Wouldn't the resistance go to zero to trigger the warning?
Thanks for your info. I have been wondering how this (goofy BMW) system works!
And why do they always call for new sensors when changing the pads?
Jim

[Ric in RVA]

Originally Posted by jlc45

Hey Ric. Are you sure your explanation is correct? Wouldn't the resistance be "infinity" if the wire is cut? Wouldn't the resistance go to zero to trigger the warning?
Thanks for your info. I have been wondering how this (goofy BMW) system works!
And why do they always call for new sensors when changing the pads?
Jim

They replace sensors if you have worn them down.

When all are uncut the resistance is zero. current freely flows.

When the first wire gets cut current flows through a 470 ohm resistor. The computer sees that and know how much wear has occurred.

When the second wire gets cut the resistance goes to infinity and the computer knows you are almost done.

From a Bentley manual.....

[mr.fabulous]

So all I have to do is short the two ends together? I have caliper bolts and a new sensor on the way (ECS)... but I will try that first just to see what happens.

The last thing I need is for the car to tell me when its brakes are worn. When my front sensor broke while I was changing pads back in January, I wondered what the smarter-than-me electronics in this car would think of that... but it's not like I had a spare sensor handy, and so I cut the thing and tie-wrapped it out of the way. Car did not complain... until a few days ago.

[blinded]

You are completing the circuit when you tie the two ends together. When I broke one of the sensors, I did the same. I did that before tripping an error though, so you'll need to also reset that.

[beattiecj]

Had same issue last week, you cannot reset the brake until you throw on a new sensor... I know super annoying, at least it isn't the rear where you have to remove the fender lining to replace it.

[WDE82]

Originally Posted by mr.fabulous

So all I have to do is short the two ends together? I have caliper bolts and a new sensor on the way (ECS)... but I will try that first just to see what happens.

The last thing I need is for the car to tell me when its brakes are worn. When my front sensor broke while I was changing pads back in January, I wondered what the smarter-than-me electronics in this car would think of that... but it's not like I had a spare sensor handy, and so I cut the thing and tie-wrapped it out of the way. Car did not complain... until a few days ago.

Just a matter of luck. I bet some strands were touching until recently. Just strip the ends and twist or solder them together.

Originally Posted by beattiecj

Had same issue last week, you cannot reset the brake until you throw on a new sensor... I know super annoying, at least it isn't the rear where you have to remove the fender lining to replace it.

Or short out the old ones.

I don't get how it's "super annoying" though. You CAN reset the computer with the worn sensor, but it immediately reads the worn sensor again and puts the warning back up.

These things are like $10. IDK why you guys don't just buy them.

[Mr Gasser]

on this video bypassing the sensor seems to magically reset the brake warning.

[mr.fabulous]

Cut off enough of the end to twist & sodder the two wires together and no more warning. This allowed me to reset both the front and rear brake wear indicators; interesting that the front having gone to totally open also affected my ability to reset the rear. I'll install a new sensor the next time I have that caliper apart... like I said, the last thing I need the car to tell me is when it needs brakes.