O2 sensor, which one???

[llerrad]

1999, Cav. 2.2, O2 sensor behind the cat. converter has crapped and the parts people asked primary or secondary O2 sensor.
I don'k know. anyone tell me which is which, the one on the engine man. or the one behind the cat. conv. under the car.

[OverAllComa]

primary = before cat
secondary = after cat

[Lances133]

Originally Posted by llerrad

the one on the engine man.

I believe that's the header, just for future reference.

[Derk_eliso]

technically, it's in the flange that connects the downpipe TO the headeR lol.

[Lances133]

right but the 02 sensor's socket located in the header

[Classicrocjunkie]

If you use a code reader, Bank 1 is before cat, Bank 2 is after. Do not replace the Primary O2 sensor with a Bosch one. They are notorious for crapping out and failing. I've returned 3 of them for our cars in my store. Single wire ones from the dealership are around $65 bucks. Get a delco replacement for the primary, secondary you can use bosch.