Diagnostic Codes Disabled In Dialer? I have a Huawei Ascend Y300 running on Jelly Bean and I can't get any diagnostic code to work on the dialer... The only thing that works is the code for displaying the IMEI: *#06#

Every time I enter a diagnostic code like *#*#4636#*#* or anything else, it merely continues to display the dialer. :-/

I've tried looking for the stock Jelly Bean dialer but I haven't had any luck. How do I fix this?
It's possible that your phone does not support the code. If you look at one of the comments in the askvg link you shared in the comment, one user says: LCD TEST Does not work for Galaxy S2. However, another user replied that it is supported, but with a different code.