1988 Cadillac Sedan DeVille, 4.5L
I am trying to test my EGR valve using the on board diagnostic capability built
into the digital dash. However, the ECM will not enter the "ECM Output
Override" mode. I can get to all other modes. Once in the "7.0 System Ready"
mode and I can hit the "HI" button, and it will it advance to the "E.9.5" mode.
However, at that point the "ECON" button will not advance to the "E.6.1" (VCC
The "ECON" button works normally when using the air conditioning, and to get to
other diagnostic modes.
Anyone have any idea why the computer is behaving this way.