not 100% sure about the PAC model but the normal EP30K model info i have shows E16 as being a Traction Stall Timer error.
So basically the truck was stalled under power/load for too long.
Setting #20 in setup sets the 'stall time' parameter for this

Also other possible causes could be:
- faulty speed sensor
- faulty wire connection
- faulty traction logic board

I think in most cases this code might be triggered from the operator pushing loads or possibly trying to drive through the parking brake (if the parking brake switch is not functioning allowing the truck to move when it is applied).
The other scenario's of possible causes are less common but still a likely cause and should still be investigated.