dm error 2/4

[tower]

Well the dreaded check engine light is flashing its face again on the W140. Need some help in the diagnostic end (really clarity). Please chirp in with any comments or suggestions.

As I understand it, DM error 2 and 4 are related in that they both use the 02 sensor to check for validity (2 is the O2 sensor inoperative, 4 is the air pump circuit inoperative, or visa versa don't remember). This rose its head about 4 months ago, so I replaced the O2 sensor with a genuine mercedes new O2 sensor. The check engine light didn't go out, flashed back on about a week later.

Anyways, I need to do more diagnostics, and am confused about the output from the x11/4 connector, pin 14, o2s I. Is it giving the O2 voltage (0 to 1 volt) or is it giving the mirrored signal translated to the reference value of car voltage for a duty cycle read (ie, if the O2 is reading 0.5v, it will give 7v if the battery voltage is 14v?.)

My first thought is to meter out the voltage signals immediately at the x3/1 connectors while the car is running but I'm at a lose on how to set up the test leads, hence I want to confirm that I should be getting the O2 sensor values from the X11/4 connector.

Further, I put the car up on a hoist, engine idling, o2 sensor disconnected and probed the connector from the O2 sensor. Was getting 0.7 to 0.9 volts out of it consistently, so it was running rich. When I probed the x11/4 lead, most of the time I got 7v but at times it would vary across the board from 0 to 3v.

Any suggestions on how to attach this?

Regards

Tower