Siphoning and throwing an error code

My first thought is a pump failing to discharge. Impeller issues on these pumps, a well a a jammed drain valve at the pump could cause the symptoms. This has been a source of fault codes stemming from a simple rubber flapper that has worn or broken loose. A closer inspection of the drain pump and anti-siphon flap might solve the issue.How far from the units does the plumbing come together? If they both have a 1/2 inch drain line and they come together and go into at least a 3/4 or 1 inch drain line the rest of the way, I would not worry about them backing up. I would install an air gap on each drain line from each dishwasher then as they drain away from the air gap, tie them together with the larger line that goes down to the trap. That should eliminate your siphoning problem.