OK so it sounds like the sensor ground is missing and that is the cause of your high STFT.

The ground to the sensor on the Blue/Purple wire is fed directly from the ECU. It is Pin 8 on the Red ECU connector (See diagram).

Suggest you try a test at the ECU connector (again by back probing the connector). Do a resistance test between that pin and a good ground. Should be close to 0 ohms. (The ECU is in the RH Footwell behind the kick panel)

If the test is successful at the ECU connctor then that would suggest a broken wire between the ECU and the sensor connector that you will need to trace and repair.

However, if the test shows high resistance to ground at the ECU connector then the fault is either
- the ECU
- the connector (more likely)

Remove the connector and you may find a broken/dirty/corroded pin which will need to be repaired.


Before the above, you could try to just jump a good ground connection to the Sensors at the Blue/Purple wire - in theory that should make your car run properly and the STFT should drop to normal levels. If it does then you know by fixing the ground signal you will resolve your issue.

 

b1mcp you made my day incredible , you don't know how thankful I am. I hope this is the case of my problem.

Today wanted to test the ECU ground, opened the cover but was not able to reach the connector without removing the ECU itself. Without removing it I can't reach the wire with the tester.

Since i had to drive the car soon, i didn't dare to start moving the wires and connectors all around in case i make something worse.

You mentioned there is a possibility just to jump the ground wire to good ground and it should be the same as ground from the ECU.

If I jump the wire from the sensor ground, must i jump both sensor wires, or as it shown in the scheme, that both sensors share the same ground wire?

Basicly I ground any of sensors ground wire to body and it should be enough to test if its functioning.

 

Yes I think jumping a good ground to just one of the Blue Purple wires should be enough as it is a shared ground.

Good luck.

 

So guys, wanna tell that the story had a happy end.

After trying all the aspects with lambda grounding, jumping good ground as I thought that was that case - it wasn't the case.

I even tried to leave this issue as is, but failing at MOT CO emissions took me to further actions and research.

I found a good car electrician with some diagnostic software, told him my story and he solved my problem in 4 hours.

It was a broken connector pin at a O2 sensor heating cirquit. Repaired and problem solved.

To my wonder the sensor heating appears to have a big impact on sensor behavior and the way ECU understands the signal.