Hi

The car in questing is an 1994 W124 E220 w/M111.960 engine which
failed the MOT test due to high CO (way out of spec).
Keeps getting fault code 9 on ECU:
9 O2S 1 (before TWC) - voltage too high, circuit open or voltage implausible.

The lambda sensor have been replaced in 2011 with a universal type.
When measuring the lambda signal I am getting a very low signal, 0,02V-0,06V.

When measuring the same signal with the lambda signal disconnected from the ECU I get a fluctuating reading of 0,4V-0,6V (directly from the Lambda sensor).

The "ECU lambda signal in" cable also has contuinity to earth?.
If I disconnect the wiring loom from the ECU there is no contuinity to earth.

How can the signal change so drastically when i connect the Lambda to the ECU and is the "ECU lambda signal in" cable supposed to be connected to earth?

All help is highly appreciated