One thing is certain, if you got low voltage, the KJ is not going to be happy about it, and it will throw codes.
First check the battery electrolyte level (if battery has removable caps) and fill to above cells if low, not all the way to top, with distilled water. Clean the terminals if corrosion present.
Manually charging a weak battery for 24 hours at 2 amps and then having a load test done on that battery is in order. If battery replacement is required find one that has a higher rating at 800 CCA (cold cranking amps)
Also ensure that the alternator is putting out more than 14.5 volts while running.
Then clear the codes, and see if anything else shows up.