Replacing O2 Sensors

Seems like a lot of guys do up and downstream sensors.
I was under the assumption that only the upstream needs replacing.
I thought if you get a code for downstream, it tells you Cats are dying.

also, what’s the preferred brand?

 

Denso. $55ish each.

 

Downstream O2 sensors go bad as well as the upstream ones. Never assume it’s the CATs or it’ll be a $500-$2000 mistake.

 

Jack nailed it pretty good.
Also I’ve heard Toyota computers are very finicky with cat Efficiency
Thresholds. Your cat isn’t “CLOGGED” but it’s probably a Lil dirty to where it’s not exactly cleaning up gasses like Toyota wants it to, so it throws a 420 code.
Throw a Fowler on the rears if your getting a rear o2 code

 

I looked on Amazon. They only listed downstream units.
Got a part number for upstream?

 

Try the Denso Dot Com and enter for more info.

 

I worry about my post cat o2’s because I’ve looked at them and god knows they are not coming out.