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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Tue, Jul-17-2018, 03:37:28 PM   #1
Texaz3
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Default Brake switch, ASC sensor, or both?

I have an intermittent issue with my ASC and /or brake switch. Sometimes I get brake switch fault on OBC, goes away on restart and might not come back for weeks. Same with ACS light, might get a light while driving, usually goes away on restart and might not come back for weeks.

Am I dealing with failing speed sensors and brake switch? Or wiring/electronics issues? Could one be related to the other?
Brake switch issue appeared first. Any input welcome.
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Old Tue, Jul-17-2018, 06:31:21 PM   #2
NolliM3
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Default Re: Brake switch, ASC sensor, or both?

That's the normal behavior of the brake light switch when it's bad...it seems to last about two years...I can say to the ASC as my car doesn't have it.
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Old Tue, Jul-17-2018, 06:53:27 PM   #3
Texaz3
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Default Re: Brake switch, ASC sensor, or both?

Ok, I have ordered brake switch, seems like a pita to replace.
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Old Wed, Jul-18-2018, 03:50:54 AM   #4
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Default Re: Brake switch, ASC sensor, or both?

Its not hard, but Id suggest taking your drivers seat out. Takes 20 mins to save 30 mins of being upside-down.
I've never heard of the switch causing ASC issues however. Any ABS lights?
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Old Wed, Jul-18-2018, 04:01:17 AM   #5
Texaz3
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Default Re: Brake switch, ASC sensor, or both?

Nope, no ABS lights. I need to scan stored codes, maybe there is something that could shed some light on this.
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Old Wed, Jul-18-2018, 06:19:08 AM   #6
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Default Re: Brake switch, ASC sensor, or both?

Check the tension on the ASC actuator cable. The cam should be fully seated against the stop and the cable should to taut without pulling the cam off the stop. It is very common to see this cable loose and the same goes for the throttle cable.

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Old Wed, Jul-18-2018, 06:24:52 AM   #7
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Default Re: Brake switch, ASC sensor, or both?

You can change out the brake switch quickly by removing the knee covering and the metal/foam guard underneath it. Leave your seat in and use a rod against the seat to depress the brake pedal (move your seat and lock it in place to keep the pedal down). To remove the old switch, completely pull out the white adjustment plunger. This will free the red locking collar (just pull the collar apart, may require a trim removal tool/flat head) and the switch can easily pry out. This is something I can do by feel now. It's a very easy process once you understand how it all works.

Install is very easy. Make sure the white plunger is in but at full extension. Install the switch and push the red collar in to keep the tabs held in the metal bracket (ensure you are squarely in the bracket or the switch will pop out on first pedal release). The first time you fully release the brake pedal it will self adjust the plunger.

On that note of the white plunger; You can depress your pedal and pull it out to max extension (don't remove it all the way). Let it self adjust again and you might find your lights working again (or no OBC error reporting). You can also clean the contacts in the switch to restore functionality but there is a point where they break or just punch through the copper.


Last edited by Braymond141; Wed, Jul-18-2018 at 06:44:57 AM.
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Discussing My 99' Hellrot intro in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)