There are a lot of terms that I trow out and most have extensive discussion in those phrases in the archives. I have writen detailed descriptions of "closed loop" and "EHA monitoring criteria" on these forums more than once; and so have others.

The term closed loop is not just an automotive term. It refers to a method of control. Basically it means that in order to do overall control one designs a system to do a function with measurable output. One then monitors the output and changes the input to keep output exactly within bounds. In an auto engine management system the O2 sensor is used to do the measurement of output (exhaust oxygen content to be exact).

From your EHA readings it sounds like there is no feedback control (another variation of the closed loop concept). That is the purpose of the "through the Captain" test. It will give you your controllers capabilities.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician