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AC Causes Break and DSC Lights

2K views 3 replies 2 participants last post by  Ginkgo 
#1 · (Edited)
Brake not Break...

I have a 2005 R52s. Since the day I bought it, I've had problems with the brake light and DSC light coming on at what first seemed random. After some testing I've been able to narrow it down to this:

If the ac compressor isn't on, the brake light will not come on. If I have the AC on at low speeds, like around town, the brake light will come on, followed about 45 seconds later by the DSC light. It's always in that order. If I get up to speed, or turn off the AC the Brake light will go off but the DSC light will not. If I'm running interstate speeds with the AC on I get no error lights. Confused yet? It get's better.

If I'm running interstate speeds with the AC on, and turn my windshield wipers on, they'll go up, then on the way back down they will slow, then stop. I have to wait a few minutes, to try and get them back down. If I don't have the AC on, they will work perfectly fine.

The headlights and or fog lights can sometimes cause the wiper failure as well.

And this is the handbrake light, not the brake wear sensor light.

The battery seems fine, even with a load I'm getting around 13v at the battery terminals, and at the battery terminal under the hood.

I'm pretty confused at this point, and don't know what else to try. Any Ideas?
 
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#2 ·
Good old mini electrics!
First thing that springs to mind is the body control unit(bc1) I'm pretty sure all of those systems run through it. Check for loose connections, broken wires or water ingress. On my right had drive r53 this unit is behind the plastic trim in the drivers foot well. I assume it's the same in a lhd?
Other possibility is the abs unit, I had lots of electrical problems including fault lights, air con, speedo etc and after many months of searching, there was a broken wire not too far from the abs unit behind the glove box and above the fuse board. It had actually broken inside the undamaged sheath and I only found it when it stretched!
I'd get a diagnostic done, if there's an independent garage near to you with decent equipment to do so, failing that then main dealer. This should narrow down your search. Can't remember the codes but the issues I had were related to a lack of 'can bus signal'
Btw both of the units I mentioned are coded to your car so if they do need replacing it's either a brand new one, coded to you car by BMW or if you can find the exact secondhand unit, they will need recoding with specialist coding equipment.
Don't forget to post again when you fix it, it's always helpful to have solutions to problems which others might have!
Good luck :)
 
#3 ·
Hey Ginkgo!

I've been checking wires the wires around the ABS, but haven't found anything yet. I'll double check around the BC1 as well.

I've got my bluetooth ODBII, but it hasn't been able to find any errors. Is there a specific computer that reads Mini codes better than another. I can call around and ask the shops. There isn't a dealership within 2 hours in any direction, plus they charge nearly $200 just to look at it.
 
#4 ·
Hi
Mine was diagnosed using 'auto logic'
This is a professional diagnosis computer which is also used by BMW. Luckily for me, my neibour is an independent bmw specialist so it just costs me a drink to plug in! The kit costs £10k! So not many shops will have it.
Most of the home use OBDII tools are only good for engine/emissions codes and have limited diagnosis abilities. Which may be why yours is not showing any errors.
If you can find someone local with autologic I'd go with them, as its as high end as you can get. otherwise maybe a 'snap on' machine might do, but I've not tried one.
Hope that helps:) let me know how you get on
 
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