Thanks for responding. I checked the ratio key on, engine off as you suggested, and got a steady 85%. This was what you said a california car would display. I was surprised to find that this is a '91 california car, as it was purchased new in Oklahoma in '91. I purchased it used in '99. To further confirm this I was reading in the CD manual and found that for '88 to '91 california cars, they provided an on-board diagnosis system with a switch and LED at the X92 connector to show and clear DTC's. Further, it says that you have to use the DTC switch to change between on/off ratio output or DTC output. I haven't been able to check it yet, but am sure that it wasn't outputing ratio data to pin 3. I'll check it after work and post the ratio results.
By the way, I'm still a little suspicious that this is really a california car (even though all the evidence says it is). How can I verify this? The VIN is WDBDA28DGMF827214. Can I tell from here.
I haven't checked the O2 sensor yet. Once I get the ratio figured out, I'll check that. Thanks for taking time to respond.
'91 190E 2.3