Just an update for anyone who may find this post with a similar problem later...
Loco returned from Bachmann Service (replaced I think) in good working order within around 2 weeks ...From and To New Zealand....Great service... :-)

Thanks for the replies....I contacted service dept and have sent loco back.....

Hi there,

I'm fairly new to model railroading...and completely new to DCC...
I have just purchased New, an Ez Command DCC Control System and two Bachmann N62454 EMD GP-7 Diesel Locos with built in DCC.
Following the instructions, I changed channels successfully from the default 3 to 1 + 2 respectively...and for a short time everything ran as expected.....I was even able to run a DC Bachmann 2-6-2 Steam Loco on channel 10.
Then one of the locos (Channel 2) stopped responding.....
Despite a fair bit of internet searching, I'm at a loss what to do to troubleshoot..... I've tried selecting other channels in case I inadvertently swapped the encoder channel.....I've reset the loco on the track numerous times in case it wasn't sitting right......I've tested the voltage throughout my layout and all is good except for the isolatable spur where I 'park' the DC loco when not in use. The working DCC loco works fine around the complete layout as does the DC Steam Loco......
What is likely to be the issue and how do I troubleshoot/fix....Is there a factory default reset...??
Any help greatfully accepted.