Brake Light Switch swap causes EPC Light, Battery Drain, Transmission issues and more
12-11-2018, 05:53 PM
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Location: 2021 SQ5 2007 Q7 3.6
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Brake Light Switch swap causes EPC Light, Battery Drain, Transmission issues and more
I've recently been dealing with some odd issues.
I couldn't leave my car outside as the battery would drain.
If I drove the car, the transmission wouldn't shift into 2nd until it warmed up, manually shifting to 2nd would get past this.
EPC light would come on.
Stabilization codes would show up.
Battery wouldn't fully charge.
Alternator wouldn't be higher than 14.1 while driving
Transmission would suddenly lurch randomly
I finally realized my Brake Pedal Light Switch was going bad. During warm weather these issues were non existent. When the car would sit outside in cold weather 30F 2+ hours the brake lights would suddenly come on. They stayed on till the battery drained. I think they would change to bumper lights when battery was very low.
Anyway I finally caught it doing it one day and smacked the brake pedal which caused the lights to turn off.
I ordered a new brake switch as it obviously was bad.
I made a video of the replacement and tear down of the switch.
These original brake switches are poorly made and will fail eventually.
The replacement one is a new design and I assume is better made.
I note in the video to not remove your brake switch until you have a replacement in hand, as taking it out risks causing total failure in the mechanism which defaults the switch to brake lights on.
On my 2007 Q7 it was pretty simple to chance 2 Torx 20 screws then the ability to twist your wrist.
After replacement the alternator sits around 14.7-14.9 volts and battery at around 12.7 instead of 12.5 after a drive. I believe 12.65volts is the proper full charge voltage, my meters dont do 100th's. So most likely are rounding up.
I couldn't leave my car outside as the battery would drain.
If I drove the car, the transmission wouldn't shift into 2nd until it warmed up, manually shifting to 2nd would get past this.
EPC light would come on.
Stabilization codes would show up.
Battery wouldn't fully charge.
Alternator wouldn't be higher than 14.1 while driving
Transmission would suddenly lurch randomly
I finally realized my Brake Pedal Light Switch was going bad. During warm weather these issues were non existent. When the car would sit outside in cold weather 30F 2+ hours the brake lights would suddenly come on. They stayed on till the battery drained. I think they would change to bumper lights when battery was very low.
Anyway I finally caught it doing it one day and smacked the brake pedal which caused the lights to turn off.
I ordered a new brake switch as it obviously was bad.
I made a video of the replacement and tear down of the switch.
These original brake switches are poorly made and will fail eventually.
The replacement one is a new design and I assume is better made.
I note in the video to not remove your brake switch until you have a replacement in hand, as taking it out risks causing total failure in the mechanism which defaults the switch to brake lights on.
On my 2007 Q7 it was pretty simple to chance 2 Torx 20 screws then the ability to twist your wrist.
After replacement the alternator sits around 14.7-14.9 volts and battery at around 12.7 instead of 12.5 after a drive. I believe 12.65volts is the proper full charge voltage, my meters dont do 100th's. So most likely are rounding up.
12-13-2018, 03:26 PM
#3
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No codes related to the brake were seen.
a code for stabilizer intermittent or something was present, no light for it.
EPC turned on a few times
Battery was not charging fully
Transmission randomly would go out of gear
Would not shift beyond 1st gear automatically
Battery would drain
all these are nightmares if you brought it to the dealer.
Tthey would start throwing parts at it and after $5000 in repairs they would finally replace the brake light switch and send you on your way.
a code for stabilizer intermittent or something was present, no light for it.
EPC turned on a few times
Battery was not charging fully
Transmission randomly would go out of gear
Would not shift beyond 1st gear automatically
Battery would drain
all these are nightmares if you brought it to the dealer.
Tthey would start throwing parts at it and after $5000 in repairs they would finally replace the brake light switch and send you on your way.
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