The only error code for the EPS (electric power steering) is battery voltage. The power steering runs from the 12-volt battery so double check the battery voltage, negative ground connections (I found an issue with the chassis ground on my 2011), and all wiring harness connections associated with the power steering unit. Since your problem was intermittent at first, there is likely a loose connection somewhere in the 12-volt circuit.
Edited to add: If you connected the booster battery directly to positive and negative terminals of the LEAF battery, a loose or corroded chassis ground connection would still cause voltage drop to the auxiliary systems in the car. Use your multimeter to check the chassis ground connection by measuring the voltage between the negative battery post and the body of the car with the car in Park, parking brake set, in Ready mode, and with high beam headlights on. Any voltage reading higher than about 0.2 or 0.3 volts is cause for concern. Voltage from positive battery post to car body under these conditions should be about 13.0 volts (or higher if ambient temperature is low). I found paint under the chassis ground connection of the negative battery cable (it looks like a cable support clamp, but is actually the ground connection) so the actual ground connection was only through the threads of the bolt. I removed paint under the lug to provide more electrical contact area and reduce the voltage drop in that ground connection.
I suggest that you clear all of the codes and see which ones come back. The HVAC error codes associated with the EV system could be concerns if they come back.
Last edited by GerryAZ
on Sat Oct 21, 2017 7:31 am, edited 2 times in total.
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015