I had a spate of very random MIL codes and lighting faults, which resolved with a new battery - many of the CANBUS micro voltage sensors do not like even a slightly knackered battery.
If you are still on the original red Banner battery, I would be suspicious. My battery did not look obviously broken (held a charge, gave a healthy meter reading) but on very close inspection it had one dodgy cell. Replaced with an Exide Gel unit of roughly the same dimension.
