Zero at Short term fuel % trim
 

Hi,
my 2008 528i had check eng light. After some work done including
verified all fuses are good including those in ECU, I am more leaning
towards the O2 sensor. The code is P165F and 2CA6. The voltage readings
for B1S2 and B2S2 are seemed fine (0.5-0.7v). But no readings for B1S1 and B2S1.
Today I noticed the STFT1 is always at zero. STFT2 is OK moving up and down.
Also LTFT1&2 are OK. See attached.
Is the zero meaning the bad B1S1 O2 sensor?
Thanks
https://cimg2.ibsrv.net/gimg/5series...6594278238.png
https://cimg3.ibsrv.net/gimg/5series...f9a7341af.jpeg
https://cimg4.ibsrv.net/gimg/5series...286ca90803.png

I went ahead and changed the O2 sensor on B1S1. Same problem remains. The reading is still 0. Same P165F code with Check Eng. light on.