2013 MS3 - Flaky keyless entry

pieter3d

Member
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Bay Area, CA
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2013 speed3
A while back my car has been telling me my "advanced key" fob's battery is low, so I replaced it. Yesterday, the fob didn't unlock the car. The lock/unlock buttons did nothing, and proximity unlock with the little button on the door didn't work. I had to manually unlock it by pulling the actual cut key out of the fob. Same thing with the ignition, car wouldn't start. I was able to start it by pulling the cover off the backup key barrel, inserting the key from the fob, and holding the fob itself near the start button (apparently it has a proximity sensor).

Then after driving, it was working fine. I could unlock it with the fob or door button like normal, and it started with the button and the fob in my pocket as it always had.
This morning though, same problem again, fob not detected. After starting with the backup method, and driving around for a bit, things went back to normal again. Interestingly, the screen still says fob battery low, which it definitely isn't since that's a new battery.

So I am guessing there is something wrong with the receiver hardware in the car. That could explain the low battery warning too, if one of the antenna's isn't working well (or at all), perhaps the car thinks that's a sign of a weak fob transmitter?

Anyway - thoughts? I am guessing this is gonna be a hard one to diagnose and repair myself given this is the security system and likely requires specialty credentials to mess with. Would be nice to avoid an expensive trip the dealer....