From what I understand the on board diagnostics are all loaded on the SIMM. Without it the CADI will be required for pulling fault codes and possibly even resets. Very difficult to support without the SIMM. Supposedly an early version of CADI was leaked out but I have never seen anyone with it nor have I been able to find it. They have a special telegram they can send to the CPU that will invalidate the SIMM and make it unusable so, just because the job has the SIMM DOES NOT mean it is functional.