I was using OpenWRT in many DWR-921 rel C3 without issue.
We received some units which seems to be Polish (language on the box and system language) for which I was unable to made the wwan working. Whatever the configuration.
Error is : Network registration failed, registration timeout reached
Curiously, typing this errors sends me to... polish forums...
I tried to make comparison with a working device and a non working one.
WWAN module looks exactly the same on both devices. It's a BM806U-E1.
I tried to switch the WWAN module, And it solved the issue : this mean that taking the WWAN module from a working router, and placing it an the non-working router made the non-working router to work normally.
using ATI AT commands ont both module send the same result
Have you any clue? Is it possible to upgrade the module firmware?
Note that with Stock firmware these router were not working initially. It was necessary to upgrade to a new stock firmware (3.015) solve the issue and the router were working correctly.
I tried to update to OpenWRT AFTER the upgrade, but this made no difference.