You could do a visual check of all electrical parts, make sure no cables are damaged or stretched or twisted and all look to be in their proper place. Any expose-able contacts could be cleaned with switch cleaner and a cotton bud. Some people use cable ties and insulating tape to make sure the systems are sealed from the elements.
A lot of problems for these systems seem to be around the torque sensor in the crankset area. Looking at the general view of the Suntour ebike system it seems to offer exceptional value offering a low cost freehub based motor hub with a torque sensor (not the simple cadence sensor of more basic ebike systems) and you get the reliability and simplicity of a motor hub however the torque sensor has had some issues with internal cables breaking and the housing snapping. Even though E04 is nothing to do with the torque sensor I would definitely check that area first to make sure it's all in good condition.
It could be resistance in the cables/contacts is causing the computer to sense a high current draw which it relates to E04 but in reality it's because you have dirty contacts.
I'm curious how the Carrera e-mountain bikes cope with off-road use as the bottom bracket area can often get frequent minor impacts on normal mountain bikes and this is where the torque sensing electronics are and I wonder if they are over exposed to possible damage. What do Carrera's e-mountain bikes have fitted there to protect them. Not such an issue on their ebikes meant for road use like Subway's and Crossroads.
Lastly the crossfire is famous for lots of suntour related problems so some good info there. Not a bike that ever interested me as I hate hybrids with low end front suspension just don't see the point of it for 99% of riders but it was Halford's pioneering Carrera ebike and it uses the same Suntour system.
