O2 sensors Calif '03 PreRunner

How many O2 sensors are there in a 2003 PreRunner SR5 TRD 3.4 V6? I'm reading about two or four, but no continuity of information, even Chilton's is void of this info. Is there a difference if the truck was bought new in Calif?

 

It’s neen quite a while since I had my 01 4R with that engine but I believe it’s 4 of them. Most have a pre and post cat and the bank 1 is cylinder 1 side bank 2 cylinder 2 side.

 

Underneath my 2001 V6 2WD Prerunner, I've got two of them.

Even bought one as a replacement (upstream) but I've yet to install it. If you want a picture/part number I'd be happy to take one for you when I get home.

 

Good point here might just be a pre and post after both banks merge and only 1 cat.

 

Yeah there should only be 2 of them. One thing of importance to note in Cali emissiom trucks is that the upstream sensor is wideband, meaning its an Air/Fuel sensor and not a regular O2 sensor like the downstream is.