Iphone 4s wifi gray out problem is hardware problem, the wifi chip got welding off (or called fake weld). This is nothing to do with software upgrade.
I just fixed my iPhone 4s with gray out problem. This is not same as the way others talked --heating and cooling. this method needs to open iPhone case.
here is how (with phone power off):
1) open case (many youtube videos will teach you how).
2) remove metal covers, you will see the wifi chip (within red lines.);
3) carefully (with a sharp knife) remove the black insulation layer completely (red lines), will put insulation layer later.
4) after remove the insulation layer, you will see the wifi chip like this picutue ( I borrow this picture. wifi number and ID is blacken out):
5) then, heat-up your solder iron (40-60 W is OK).
6) use a wood stick, press down in the middle of wifi chip (black big dot in the middle). then use the tip of solder iron to push each blue dot about 20-30 seconds tightly, the heat of soldering iron will be passed to the chip to do re-soldering work. you need to do this step with 8 dots one by one, not stop.
7) after soldering work, put back black insulation layer back.then resemble the iPhone 4S.
the Job is done and your wifi should work now.
Good luck.
( this is only for those Iphone 4s with warranty expired)
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