Brake Lights stay on after pedal released (engine running)

M

MyOtherCarsA_UFO

Member
I recently purchased a 2003 BMW Z4 3.0I Automatic knowing the brakes were not functioning properly. Here's the issue:

With the ignition turned to ACC, the brakes function perfectly. In RUN the brakes stay on after one pedal application, but can be reset with turning the parking lamps on and off again. They can also be reset with the turn signal/high beam arm. With the engine on and running, the brakes will turn on with the first press of the brake pedal and then remain on after released. They cannot be reset using the previously mentioned methods. They only shut off after engine is shutdown.

Already replaced the brake switch at the pedal, no change. Shot the lighting fuses for unusual voltage and they seemed fine. I tried bleeding the brakes and that didnt help. Looking at the schematic it looks like it could be an issue with the ignition possibly, or the "light switch cluster" which I'm not entirely sure what or where that is. I'm pretty stumped on this and would appreciate any help. Thank you!
 
LCM module controls lighting - there is a circuit board behind the main headlamp switch, so I would probably start by changing that. Any replacement will need coding to the car unfortunately as it also stores things like vehicle mileage. The brake lamps (like lots of other electrical things on the Z) run from a CANBUS, so you may have some corruption on the data line. This is usually caused by the airbag control module getting wet. It’s located underneath the coin holder in the centre console.
 
Just a thought, is there also a pressure switch on the brake servo? Maybe this switch has some influence on the brake lights as well as the pedal switch.
 
MyOtherCarsA_UFO said:
In RUN the brakes stay on after one pedal application
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MyOtherCarsA_UFO said:
With the engine on and running, the brakes will turn on with the first press of the brake pedal and then remain on after released.
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I just want to check whether when you say the "brakes" stay on, you mean brake lights, or are the brakes themselves remaining pressurised, braking the wheels?
 
If I’m right there’s a switch above the brake peddle that has an adjustable switch sometimes the locking nut becomes slack it needs readjusting and tightening. Hope that helps.
 
Mr roadster said:
If I’m right there’s a switch above the brake peddle that has an adjustable switch sometimes the locking nut becomes slack it needs readjusting and tightening. Hope that helps
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If you are talking a out the switch with the magnetic pickup that slides and locks in place, that's the switch I changed.
 
ph001 said:
LCM module controls lighting - there is a circuit board behind the main headlamp switch, so I would probably start by changing that. Any replacement will need coding to the car unfortunately as it also stores things like vehicle mileage. The brake lamps (like lots of other electrical things on the Z) run from a CANBUS, so you may have some corruption on the data line. This is usually caused by the airbag control module getting wet. It’s located underneath the coin holder in the centre console.
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Being that the airbag light is on, this sounds like the issue I may be having. If there is corruption on the CANBUS, is the fix to just have it re-coded?
 
MyOtherCarsA_UFO said:
ph001 said:
LCM module controls lighting - there is a circuit board behind the main headlamp switch, so I would probably start by changing that. Any replacement will need coding to the car unfortunately as it also stores things like vehicle mileage. The brake lamps (like lots of other electrical things on the Z) run from a CANBUS, so you may have some corruption on the data line. This is usually caused by the airbag control module getting wet. It’s located underneath the coin holder in the centre console.
Click to expand...

Being that the airbag light is on, this sounds like the issue I may be having. If there is corruption on the CANBUS, is the fix to just have it re-coded?
Click to expand...

If you pull the coin holder out you can see the connector for the airbag control module. Usually when it gets water in, the connector corrodes badly, rendering the module scrap. Since you have the airbag light on anyway, you may as well just disconnect the module and see if it sorts the CANBUS. If it does, you probably need a new airbag control module which I think will also need coding to the car.

It is very odd that the lights work ok with the ignition on, bit but not with the engine running though :?
 
ph001 said:
MyOtherCarsA_UFO said:
ph001 said:
LCM module controls lighting - there is a circuit board behind the main headlamp switch, so I would probably start by changing that. Any replacement will need coding to the car unfortunately as it also stores things like vehicle mileage. The brake lamps (like lots of other electrical things on the Z) run from a CANBUS, so you may have some corruption on the data line. This is usually caused by the airbag control module getting wet. It’s located underneath the coin holder in the centre console.
Click to expand...

Being that the airbag light is on, this sounds like the issue I may be having. If there is corruption on the CANBUS, is the fix to just have it re-coded?
Click to expand...

If you pull the coin holder out you can see the connector for the airbag control module. Usually when it gets water in, the connector corrodes badly, rendering the module scrap. Since you have the airbag light on anyway, you may as well just disconnect the module and see if it sorts the CANBUS. If it does, you probably need a new airbag control module which I think will also need coding to the car.

It is very odd that the lights work ok with the ignition on, bit but not with the engine running though :?
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Any tips on how to remove that center console without breaking every piece of plastic along the way lol?
 
Have you tried just removing the coin holder first to inspect the module / connector? I can’t quite remember how much access it gives you.

If you suspect the module, then there are a few guides on here regarding removing the centre console. It’s not very pleasant unfortunately.
 
UPDATE:

I disconnected the plug at the DSC that sits unter the brake fluid reservoir/master cylinder and the brakes functioned perfectly. Not sure what to do with this information but I feel it's a start in the right direction.
 
If you are talking about the DSC pressure sensor that screws into the master cylinder then it may well be your problem if disconnected the brake lights return to normal function on/off.Here is the patrts diagram https://www.realoem.com/bmw/enUS/showparts?id=BT53-USA-03-2003-E85-BMW-Z4_30i&diagId=34_1290
Replacement would be the only way to confirm this, it would be difficults to bench test it as it would need pressure to test it with a volt meter to test its circuit.
Ebay item https://www.ebay.co.uk/c/20017016106 and https://www.ebay.co.uk/itm/ABS-DSC-Stability-Control-Pressure-Sensor-For-BMW-E46-3-5-6-Series-34521164458/312700437092?hash=item48ce660264:g:SToAAOSwE5BdLE0E
Under a £10 so well worth a punt to see if it fixes the problem.
 
That is a bizarre fault if its the DSC pressure sensors. Don’t understand how they could possibly be connected, the DSC sensors always bring on the abs & dsc dash lights too. Very odd indeed.
 
Can you put a code reader on the car and see if any codes are set, might narrow the fault down, INPA or BMW Scanner 1.4 should read the modules ok.
 
colb said:
Can you put a code reader on the car and see if any codes are set, might narrow the fault down, INPA or BMW Scanner 1.4 should read the modules ok.
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The codes it was throwing last time it was hooked up are;
0x5E5C(24156) "RPA Push Button Error>Not currently detected."

05D8F(23951) "Sensor Cluster Internal Failure>Currently Present: Warning Lamp On"

0x5E38(24120) "Yaw Rate Sensor Electrical Failure> Currently Present:Warning Lamp On"

Those were all under ABS/DSC on the scanner.
 
colb said:
If you are talking about the DSC pressure sensor that screws into the master cylinder then it may well be your problem if disconnected the brake lights return to normal function on/off.Here is the patrts diagram https://www.realoem.com/bmw/enUS/showparts?id=BT53-USA-03-2003-E85-BMW-Z4_30i&diagId=34_1290
Replacement would be the only way to confirm this, it would be difficults to bench test it as it would need pressure to test it with a volt meter to test its circuit.
Ebay item https://www.ebay.co.uk/c/20017016106 and https://www.ebay.co.uk/itm/ABS-DSC-Stability-Control-Pressure-Sensor-For-BMW-E46-3-5-6-Series-34521164458/312700437092?hash=item48ce660264:g:SToAAOSwE5BdLE0E
Under a £10 so well worth a punt to see if it fixes the problem.
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I disconnected the electrical plug at the DSC (I'm honestly unsure of the nomenclature, but it has hydraulic lines that appear to run to each wheel) and in doing that the brake lights operated normally. After disconnecting this plug the speedometer, odometer, and power steering stop working if that helps you to understand which plug I'm referring to. I tried disconnecting (electrically) the individual sensors attached to the master cylinder, but that didn't cause a change.
 
Good read here which might assist https://www.youcanic.com/wiki/bmw-dsc-abs-problems
The RPA fault would appear from a google search to be the tyre pressure monitoring system, check connections at the reset switch.
Sensor Cluster Internal Failure appears to be related to the ABS DSC system sensors, check all wiring
Yaw Rate Sensor appears its not seeing any volts, check fuses and connections
What make of scanner did you use to view the codes?
Were these codesvpresent before or after you tried unplugging sensors in the system?
 
Another thread running here with brake lights stuck on, sounds like retro fit cruise control is causing the issue, wired up wrong.
By any chance has your car had cruise control retro fitted? If it has check out the wiring is correct as per the linked thread.
https://z4-forum.com/forum/viewtopic.php?f=2&t=120423
 
Result in on that other thread, it was fuse 14 that had blown causing brake lights to stay on apparently.
 
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