Xperia Z 4G LTE for T-Mobile connection problems

[Tragico1]

I purchased the Xperia Z 4G LTE for T-Mobile (C6606) from the Sony store about a month ago.   For the first 2 weeks it worked great - I was getting 4G LTE coverage almost everywhere I went in town  (and 2G/3G otherwise).    Then something happened about 2 weeks ago, and now I cannot get any quality cellular phone or data connection. 

That day I was using Wi-Fi at my office, because the cell signal is very weak inside the building.  When I left work I had trouble finding the T-mobile network.  Since then, I have 0 bars or the Red "X".  When I search for networks, I either do not see any networks or re-register on T-mobile only to have a weak signal for a short time before it was lost again.    

I had used Wi-Fi at work, home and other locations and had no problems reconnecting to the cellular network prior to that day.   I mention this about Wi-Fi because I have seen other posts about there being a potential bug related to the Location-based Wi-Fi feature.  I have tried diabling that feature without any improvement. 

I have also attempted these fixes with no success:

* Power cycle, remove & reinsert sim.

* Have T-mobile reset my connection

* Used the "Update Service" to make sure my device was up-to-date.

* Full factory reset.

Please help!

[Uliwooly]

How about this

settings > xperia > internet settings 

[Uliwooly]

Also contact Tmobile for any coverage issues in your area

[Tragico1]

Thanks uliwooly.

Coverage is not an issue.  I've used T-moble in my city (Minneapolis) for 15 years with no coverage issues.  I have a friend with and iPhone on T-mobile sitting right next to me.  He has 2 bars (we're in a low spot) and I have no serverice (Red X).

I stopped into my local T-mobile store today to have them check the sim.  And with disgusting irony, when I show the rep my phone, it has 4 bars, and 4G LTE.  Clear as day.  The store must be next to a tower. I look like a fool to the T-mobile guy, but at least I learned the sim is fine.  

I drive away from that strong spot and it doesn't take long before my coverage drops.  I'm watching as I drive, and it's never better than 2 bars and usually No service.  My previous phones never had this problem moving around the city.  

The Xperia Z cannot perform with anything but the strongest cell signal (next to a tower) and it does not handoff from tower to tower as I move around.   This is not a sim/coverage issue.  It is a Hardware or Firmware issue that Sony needs to address.

[Uliwooly]

check this 

settings > more > mobile networks > Network mode, what do you have selected? 

also 

Accesss point names > under Bearer what option do you have? leave it as Unspecified

one more thing

settings > about phone > status > signal strength 

[Tragico1]

network mode = LTE(preferred)/WCDAM/GSM

APN = fast.t-mobile.com (it's the only option. I can unselect it by doing "Reset to default", but that doen't seem to do anything)

Signal strength = -113 dBn 0 asu

[Uliwooly]

tap on the APN and check the bottom 

[aye007]

My xperia z 4G is no working in network.This may be 4G root error.Network maximum bar is 2bars.Sometimes it will be Red "X" near mobile tower.How do explain it? Please answer.