Notme... are you using 2.4g control ?.. if so are both cars bound to the same controller...if so is the cut off issue similar to both cars ?....
I've seen cars do this 'shut off' thing when the driver is using 2.4 control system...it seams be a known issue with some makes and might be what's happening with you.
I run 2.4 myself but have not had issues, just thought I'd throw a suggestion out there
J