OBD II Codes P0160/P1117/P1121

[Barteur]

Hi all,
Last weekend CEL lighted up.
Ran to buy a code scanner.
I got the following codes P0160/P1117/P1121 earlier this week.
Did some research and I have been oriented with the following possibilities
-Issue with wiring of the O2 sensors;
-O2 sensor burned out.

I found the test procedure to check if an O2 sensor is ''kaput'' and might try this this weekend.
Also FYI I did change the IMS bearing and Clutch two weeks back I don't see the link unless we hit something while doing the work. Also I forgot to put back the Cam plugs when I finished the job and realized that after my test drive... (just in case this could have an impact on this)

Anyone can let me kow if I am on the right track? Also I saw that if one O2 sensor is gone change all four
I am having an issue changing something that is still good... (I only do this for IMS berings ).
Thank you in advance
Car is a 99 base
45000 miles
Regards!
Eric