In my late 1999 XK8 I finally replaced a pre-cat air/fuel mixture sensor, but I still get restricted performance warning and my generic reader gets P1638 and P1642 codes stating "DTC definition not found". Is it the ECM unit now...What can I do next, except to call a junkyard?

 

P1642 CAN Link Circuit


P1638 CAN Link ECM/INSTM Circuit/Network


That's a start. I've read something here, recently on these but can't place it.

 

I found the knock sensor on a bank 1 was malfunctioning. I replaced it and with a new air/fuel mixture sensor Bosch 15627; the car started a ran smoothly. On the bank 2 is still the original Denso pre-cat sensor234-9016. I was exhilarated. But...after about 12 miles of country roads the check engine light and restricted performance showed their ugly heads again. My generic OBDII reader pulled out a dreaded P1642 code and P0172 and P0174 codes. Right 4 cylinders running rich, left ones lean. Can anybody explain it? Drivability seems to be OK - but I did not drive the car for a year, so I do not have a fresh comparison. After some 5 -10 minutes the restricted performance goes off, check engine light stays, but the engine seems to be taking a full throttle thrust. Only a gas mileage dropped from 24-25 mpg on the why to 21.5mpg. I went home and measured the Short fuel and long fuel trim values at idle, 1500rpm and 2500 rpm in situ. These are the values:
SFT 1 -4.7 tp 5.5%
LFT 1 -20.3%
SFT 2 10.9%
LFT 2 19.5 G /what this G stands for?/

1500rpm
SFT 1 -10.9
LFT 1 - 4.7
SFT 2 10.9
LFT 2 4.7

2500rpm

SFT 1 -7.3
LFT 1 -7.0
SFT 2 12.5
LFT 2 8.6 (G)

can anyone interpret it in the terms what I should be looking for...
thanks. I wish, I will be able to write a final chapter for this story....soon