i have almost same problem with wideband, ...
good the see I am not the only one...
I could test a second 3.6 ECU with firmware update and wideband 4.2.
VEMS AAN ECU plug & play M55 3.6 board with firmware 1.1.96
I did all the voltage tests with the 1.1.96 firmware.
All voltages are correct.
And here is the interesting result. I did the bench test with no wideband connected but DVM and 12V lamp connected.
The voltage is rising slowly up to 11,7V and the lamp is shining brighter. At 11,7V it stays shining and showing 11,7V.
After that I updated to firmware 1.2.30 and did the same tests, after that to 1.2.32 and the same tests.
With 1.2.30 and 1.2.32 voltage is rising slowly up to 11,5V and the lamp is shining brighter. At 11,5V voltage drops to 0V and lamp is off... stays off
Driving with 1.2.32 - needs up to 10 minutes left before wideband is working.
After that, downgrade back to 1.1.96 and the same tests again. Everything works fine like at the first test - lamp stays on.
So it has to be something with the firmware...
AND we did another test with a third car and VEMS M55 plug and Play with 3.7 board in Audi - firmware update from 1.1.96 to 1.2.30 results in no wideband issues. Just fine like1.1.96.
Maybe something with older 3.6 boards??
regards