So wound replacing my SAI pump with a used one (from a fellow RS6 owner here in PDX). Installed it, cleared the CEL/code. All was good for about a week of driving, then the CEL came back on, here are the codes. The pump is definitely coming on for several minutes then turning off (have not timed it) at cold (morning starts or after the car has cooled for some time). Also the CEL just comes on randomly while driving or stopped. Have reset several times only to have it come back on again a day or so later. Any ideas ? Is there some other sensor/item to check ? Thought with replacing with anther what appears to be operational pump the issue would be resolved....

17831 - Secondary Air Injection System; Bank 1
P1423 - 002 - Insufficient Flow
17819 - Secondary Air Injection System; Bank 2
P1411 - 002 - Insufficient Flow
Readiness: 0000 1101