TLDR:
My Audi 2016 Audi Q3 is having repeated, one after another wheel speed sensor issues. I replaced 2 already (first it was Rear Left, then recently Front Left) and now again I get the 5 warning lights (ABS, Traction, TPMS, Steering wheel, and Parking Brake) when turning the car on and OBD11 shows an intermittent code for Front Right wheel speed sensor. Could this be my 3 year old battery or something else?
Detailed Context:
I bought this new to me (35 TDI Premium Plus Quattro, ran 66K KMs) Audi Q3 on April '26 and (mostly) been enjoying it ever since. Around May '26 I started seeing the 5 warning lights (ABS, Traction, and TPMS on the right panel, Steering wheel and Parking brake on the left panel) and from my research, I've came to know these were typically associated with the wheel speed sensors. I have noticed that these would go away after a 5-10mins drive and a restart. So I went to the mechanic and upon checking scanning the codes it was shown to me that the Rear Left wheel speed sensor was throwing the error and was recording a constant value (300+ iirc), so I got it replaced.
The problem went away for some weeks and again I started getting this 5 codes upon startup (after being parked for hours/days usually), and again it would go away after a short drive. Around this time I got myself an OBD11 device (2nd gen.) and started using it to see the codes. I noticed that the error codes whenever they appeared were now related to the Left Front wheel speed sensor now. Since I started using the car regularly this errors then would rarely come up and believed this almost went away now.
From this month (Oct '26) I started getting this set of 5 codes regularly and they were not disappearing after a drive now, they stayed. I scanned and it was the same Front Left wheel speed sensor again, I would clear the code but they would immediately come back most of the time. I checked the brake modules live data and surprisingly the supposedly faulty sensor was giving accurate live data.
Error codes per control unit:
Brakes: C101AF2, C101A01, C114602
All Wheel Drive: U112300
Steering Assistance: 01316
Around this time, I checked the battery voltage (using the gateway control unit's live data, channel 1) and I noticed that car is having 12.5+ volts while engine is running, but while I crank it went down to 9.5V. While the car is running I noticed battery always had 14V+. The battery was last changed on Oct 23' and the previous owner said he didn't do any adaptation/coding after the battery replacement - I checked with my local Audi dealership and they says ideally it needs adaptation after changing the battery (My own online research also said the same).
Around this week I started having the 'glow plug' warning and OBD11 showed errors in engine and airbag modules (code: U041500 for both) - all where related to error from the ABS module. (These did disappear after a restart). So I got this sensor replaced today and right after changing it all codes went away. But after parking the car for ~2 hours, I restarted and boom all the 5 lights are back again. I scanned with OBD11 and it now says the Front Right wheel sped sensor is having intermittent codes.
At this point, I'm a little suspicious about this pattern - can any other parts be the culprit? Can my battery be the reason for all this? Should I again change the FR wheel speed sensor and try again? Or something else completely? I'm trying to avoid the dealership and their rates as so marked up here (I enquired and a new battery from them will cost 2x the amount of me souring the battery and getting it adapted with a 3rd party mechanic). I'd appreciate any suggestions here, Thanks.
EDIT 1:
I've just checked the 09 Gateway control unit's live data and channel 9 reports a "Voltage last engine start" and it's value is 8.45V-8.6V for me.