Trying to clear dumpstate/logcat on unrooted HTC Sensation 4G

Hi,

My 4G running Android 4.0.3 is always low on memory, even though I have few apps and store most data on a largely empty SD card.

I have spent a lot of time searching, and many people recommend running the USSD code *#9900# and deleting the log files.  Sounds perfect, but I cannot run this -- or any -- code.

I am using the native htc dialer app to attempt entering codes.

Every code I enter gets the same response:

"Connection problem or invalid MMI code."

I have tried adding a "," to the end of the code as that was recommended in some fora -- but that didn't work either.

Can someone please tell me:

a) is there a way to run ussd codes on my sensation 4g ?

b) is there another way to delete dumpstate/logcat files WITHOUT rooting?

Thanks much,

kirkp