E46 Brake Pads Sensor

[yee7402]

Just change my front brake pads last week together with the sensor.. The problem is after driving a while the sensor light up again.. So I took it back and have the mech check and he took it out and reinstall it and it is gone.. Than drive again like an hour the sensor light up again...Took it back the next day and they change a new sensor for me, and today it light up again.. What is wrong?? Is it something more than the sensor.. The brake pads is new and I check it looks ok.. The rear wheel is ok last I check as well..Anyone experience this before..

 

[astroboy]

Pad wear sensor wire damage and got grounded along the way. Need to trace the wire for possible short circuit.

 

[yee7402]

AB,

How to trace? U mean they will have to take out the wire harness and do test?

 

[astroboy]

Look for tear lor. The sensor is a simple grounding device. When pad too thin, the sensor will scrub on the brake disc rotor, which will ground the sensor, to complete the circuit to lit up the pad change indicator.

 

[QD250]

maybe need to replace the defective new sensor?

 

[yee7402]

Already replace the sensor.. I am on my second sensor now.. I do not think it is the sensor issue now coz I doubt I am that lucky that can get 2 defective sensor... Anyway plan to have them check one more time and more throughly this round..

 

[yee7402]

Got my car over to the mech again and check last weekend... Problem still not resolve.. So we wanted to connect it to the computer to see if there is any error.. Guess what happen... the comp and my car could not establish a connection.. What is happening? Mech ask me to go back to AB to try their comp and see... and today my brake sensor is still lighting up... This is getting very irritating... Anyone any advise would be great now..

 

[BMWsociety]

me also having the same problem after replaced the brakepad and the sensor...the light is still on. Scaned already but no fault code.

 

[yee7402]

So yours is still not fix or you have found a solution to it already? If yes pls advise.. Thks Bro..

 

[BMWsociety]

still not fixed

 

[yee7402]

Sigh!!.. Yours is the front or rear?

Anyone can help us here?? A solution from some sifus will be great...

 

[jarance]

first you got to understand how the sensors are wired up. see below.

They are wired in series. The circuit have a reverse logic to OFF the light when it see a ground signal. so if the wire is ground then the light in the dashboard will goes OFF. If one of the sensors detect metal (disc) or it is damaged or wire is broken, it will becomes high impedance and cause the light to turn ON at the dash board.

 

[yee7402]

Jarance, The sensor are new and hence I took it out and check a few times and change a few sensors to check... The light keep on coming out after a short drive especially over bumpy roads. I can confirm the sensor did not break..

This is the funny part that I do not get.. I doubt it is the sensor already but must be something to do with the electronics setting maybe?? So I asked the mech to run a diagnostic with the computer and than the interesting thing is that it shows connection fail.. I cannot connect the system to my car..

 

[jarance]

yee, as mentioned by you, the sensors are new so I think your problem is most likely due to:-

1. connectors to the sensors is dirty or corroded. you need to disconnect the connector and spray with contact cleaner.

2. check the cable between the front sensor and rear sensor. They might be damaged.

I dont think this alarm is registered as it a non fatal signal. When the brake pad is near to end of its usage, this alarm will intermittent come ON and OFF when the brake pad is just near its end of life. It will stay ON continuously when the sensor get nearer to the brake disc (metal part).

 

[yee7402]

Jarance, Thanks... Can you elaborate on item 2... Cable between the front and rear sensor?? You mean the sensor cable or?

Not sure if I mention this but when I take out the sensor and fit it in the lights will go off only after a short drive it will light up again.. If I repeat my process the same will happen...

Since we are at it do you know why my car cannot be connected to the diagnostic computer?

 

[jarance]

Jarance, Thanks... Can you elaborate on item 2... Cable between the front and rear sensor?? You mean the sensor cable or?

Not sure if I mention this but when I take out the sensor and fit it in the lights will go off only after a short drive it will light up again.. If I repeat my process the same will happen...

Since we are at it do you know why my car cannot be connected to the diagnostic computer?

If you look at the wiring connection below, you can see that the rear sensor is link in series with the front sensor by a wire. (terminal 2 to 2)

The rear sensor terminal 1 is connected to ground and the front sensor terminal 1 is connected to the instrument cluster.

So that means at point from rear sensor to the front sensor that is a break, the alarm will comes on.

In my opinion, I would concentrate on the connectors first for dirt and corrosion at the front and rear.
The connectors are working in a wet and dusty environment.

Since you mentioned that you can clear the alarm temporary by disconnecting and reconnect back the sensor, I think you have a dry or bad contacts at the connectors.

you can also remove the connector at the front and measure the resistance to the chassis. It should not be more than a few ohms if the contact is good.

Also check the grounding at the rear for loose connection.

As for the non communication with your car, can the diagnostic communicate with other BMW or just cannot communicate only with your BMW. what brand or type is the diagnostic tools.

 

[yee7402]

Thanks Jarance I will give your suggestion a try these few days... As for the connection it can connect to other except my car.. I am not sure what type of tools is that.. This is the one my mech usually use to reset my system etc. Let me find out from him tomorrow..

 

[yee7402]

Just a quick update I got the thing fix.. After all this it turns out to be the rear sensor giving problem.. Am not sure why it happen.. The sensor did not break or anything.. somehow just mal function.. We did a swap and so far so good... Let's keep my fingers cross.

 

[parc]

first you got to understand how the sensors are wired up. see below.

They are wired in series. The circuit have a reverse logic to OFF the light when it see a ground signal. so if the wire is ground then the light in the dashboard will goes OFF. If one of the sensors detect metal (disc) or it is damaged or wire is broken, it will becomes high impedance and cause the light to turn ON at the dash board.

good diagram and explanation there.im new to the BMW n currently looking into gaining my knowledge to this car.hehe.
basically if sensor detect any problem in any of 4 brake pad.the indicator will show up..

so have to check all 4 la then..hhmm.nice.

 

[jarance]

good diagram and explanation there.im new to the BMW n currently looking into gaining my knowledge to this car.hehe.
basically if sensor detect any problem in any of 4 brake pad.the indicator will show up..

so have to check all 4 la then..hhmm.nice.

bro, there are only 2 brake pad sensors. one infront and the other in the back.