Exhaust ECU Modules

Bad exhaust ECU's would not cause catalyst efficiency codes to be set. Those codes are set by signals from the oxygen sensors. The Motronic (fuel injection) control units look at the signals from the oxygen sensors in front of the cat and after the cat and compare the two. When the catalytic converters go bad, the signals from the front and rear oxygen sensor starts to look the same (swing back and forth with the same frequency)

The Hyperflow cats may be the cause of the fault. You can look at the oxygen sensor function on the SD2 and capture it with the data acquisition and look at it on a graph to see how much the rear oxygen sensor voltage swings as compared to the front. I think that some Motronic control units had more sensitive parameters than others. Do a search for Hyperflow cats, as I think that other have had the same problem that you have.

 

I have yet to see a set of Hyperflows that did not cause this concern. They do not perform well enough to pass the OBD2 tests. Be sure to check emissions using the pre catalyst test ports as high HC readings will quickly destroy new cats.