Left or right, duh?
Okay, Brain fart time... problem with O2, upstream...code 21. Now there are two upstream O2s and code 21 also indicates left side.
So is the upstream O2 sensor or left one, the one under the air intake or the other side?
I keep thinking that sitting in the car the left side is the driver's side but when looking at the engine the left side is the passenger side.