E30 Electrical issues , brake pad sensor and left indicator wont flash

[zippy320]

Hi Guys

So I have a little time to do some work on the E30 , Decided to look into the brake pad wear sensors and my indicator issue .

The sensor light on the dash is constantly on , I checked and replaced the sensors , checked the wiring and everything seems fine .

I took the sensors off , Bridged both wires which should turn of the light but the light wont turn off , I took out the speedometer , checked the internals ( I read that a loose solder could cause the issue ) and I found no issue there .
I am now stumped .

My indicator , When I turn on the left indicator , I can hear the ticking , I can see the indicators working outside , but the green light on the dash wont flash .
While the speedometer was out , I replaced the bulb with a new bulb , I also swapped it out with the right side bulb and still no flashing on the speedometer .
Not sure where to even start with that . Could a relay or fuse be burnt? Seems the speedometer does not know the cars flashing?

Anyone have any ideas for me on these two issues?

Where does the Brake pad wear sensor plug into at the back of the Speedometer? I thought worst comes to worst , I could rewire the thing as the original wires seem to go into the cars complete harness .

Thanks guys for all the help! This car wouldn't be where it is if it wasn't for you guys!!

 

[Waseem 333i]

I am not sure on the indicator problem. The brakes have two sensors. One on left front and one on right back.

Sent from my HTC One_M8 using Tapatalk

 

[zippy320]

Thanks Waseem , I did check both sensors , front and back . Bridged them both and still no luck .

 

[ZaynM]

Ok, I stumbled across this a while ago, so this is not mine. If the mods are ok then I will post up the source (Another forum). Credit goes to user DJB (Not of BMWFanatics)

Disclaimer: I cannot say if there is any truth to this or not and nor can I be responsible if something gets messed up. This info is up to your discretion to use.

Hope this helps with regards to your brake pad wear sensor issue!!





Brake lining indicator light

Summary: The light is triggered either by the wire grounding (usually
against the brake rotor as the sensor is partially worn away) or the
wire breaking (usually as the sensor is further worn away). If the
sensors are fine, re-flow the solder on the instrument cluster resistor.

Operation

Most e30s with four wheel disk brakes have a brake wear monitoring
system. The system uses two replaceable sensors to monitor the front
and rear brake pad wear. The sensors are mounted in a notch on the
outer edge of the inboard brake pad on the left front and right rear.
As the pad wears, the sensor faces are ground away with the brake pad
friction material.

The sensors are simply a wire embedded in an insulating material. The
brake wear circuit is similar to alarm system wiring: the indicator
light illuminates when the sensor wire is either grounded or is broken.
When a sensor face first starts to wear against the rotor, the wire is
initially exposed and grounds against the rotor only when braking.
Later the wire is worn through, breaking the circuit. Thus the lamp is
initially illuminated only when braking, and later stays illuminated.

The sensor circuit is fed +12V through a 220 ohm resistor on the
instrument cluster circuit board, through the right rear sensor, then
through the left front sensor, then back to the circuit on the cluster.

If the wear indicator circuit doesn't work and the sensors are fine, the
most common source of problems is the 220 ohm resistor. This can be
easily tested without taking apart the instrument cluster. Turn on the
ignition to power the circuit and illuminate the wear indicator.
Measure the voltage and available current on the right rear sensor
connector. One of the contacts should read +12V, and provide 55-65 mA
to ground. The contact is the blue/white wire, not the green/yellow,
but it's trivial to probe both rather than look for the wire color. Use
the brake rotor as a clean ground.

If you aren't getting voltage or the correct current, the problem is
very likely on the cluster circuit board. Remove the board and re-flow
the solder around the 220 ohm resistor. This resistor is mounted next
to the C1 blue connector on the PC board. It sticks off of the board on
long leads. There are on-line pictures to locate the resistor, and you
can confirm the correct part by looking for the red-red-brown color bands.

This might sound daunting if you haven't soldered before, but this is the
easiest soldering task ever. Let the soldering iron warm up for a few
minutes, then touch the soldering iron tip to each resistor lead for two
to five seconds. You should see the solder surface change texture as it
melts, filling in the cracks that have grown over time.

Add a dab of silicone to mechanically support the resistor so that the
solder doesn't crack again. Don't cover the resistor, as it has to
dissipate almost 1 watt of heat if the sensor wire is touching ground.

That heat is likely why the resistor is mounted so far off the board to
start with -- the designers didn't want to use a expensive 1.25W
resistor, when a common 1/4W resistor was adequate most of the time.
But they didn't consider that worn-through sensors and holding the
brakes on for an extended period (e.g. stop-and-go traffic) are
correlated. The resistor is at 4X its power rating, and the only place
for the heat to dissipate is through the resistor leads. Now you have
the mechanical leverage from mounting the resistor far from the board
"working" the solder combined with thermal expansion cycles from the
overheating. No wonder there is cracking!

Worst-case power analysis for the 220ohm sensor supply resistor.
220ohm, 10% tolerance = 198-ohms, 5% tolerance = 209-ohms
Nominal 12V power is typical 13.8V operating, 15V hot load.
Power = V*I = V*V/R
Worst-case 15V*15V/198ohms = 1.14W
Worst-case, 5% 14.4V*14.4V/209ohms = 1.00W
Typical/nominal 13.8*13.8/220 = 0.87W
Design safety worst case 18V*18V/198ohms = 1.64W
So the designer should have specified at least a 1.25W part.

Note: I previously assumed that the lamp check was done by providing the
sensor power through the unloader relay. That would test the lamp drive
circuitry as well as the lamp. Instead the lamp check is done with a
diode isolated feed from the start circuit.

While you have the cluster out, with soldering iron at hand, re-flow the
solder around the temperature meter mounting hole. One of the contacts
is through the sleeve around the brass mounting stud. The stud pulls
the sleeve into the soft solder on circuit board to make contact. Over
time the solder deforms, resulting in bad contact. Tightening the
mounting nut will help for a bit, but building up the solder is a longer
term fix. Better, solder on a thin brass washer.

 

[zippy320]

Thank you soo much ZaynM !!! Such an awesome post , thanks for sharing! This actually gives me some direction .

I checked my speedometer and it seems fine , Checked the front left brake for voltage and im getting voltage so thats fine .

What I found was im not getting any voltage or readings from the rear right brake pad sensor wires . ( Im testing voltage on the actual wire that plugs into the sensor and not the sensor itself .)

Anyone knows where this wire goes? or where does it start from? I followed it back and it seems to go into the cars main wiring harness and from there im not sure where it goes .

Ok, I stumbled across this a while ago, so this is not mine. If the mods are ok then I will post up the source (Another forum). Credit goes to user DJB (Not of BMWFanatics)

Disclaimer: I cannot say if there is any truth to this or not and nor can I be responsible if something gets messed up. This info is up to your discretion to use.

Hope this helps with regards to your brake pad wear sensor issue!!

 

[ZaynM]

No Problem Bud!! Trying to assist a fellow Fanatic as best as I can. Glad it gave you some direction. Thanks for the rep point too!!

I am not good at reading this diagram but from this image, it seems the brake pad wear sensor seems to start at the back of the cluster at Connector 2/C2 pin 26 and goes through the sensors and then back to the cluster at Connector 1/C1 pin 21.

You might be able to better understand the diagram.

Hope that helps.