need help locating 02 sensor

[Danielt14]

i have a 99 cougar and i am trying to locate the correct sensor to change on the car. where on the engine is it at

i know that i need to find the one on bank 1

please help me.

[beyondloadedSE]

bank 1 is the rear of the engine. Theres 2 02 sensors on that side. One upstream and one downstream. Upstream is before the precat. Downstream is after the precat.

[Danielt14]

Originally Posted by beyondloadedSE

bank 1 is the rear of the engine. Theres 2 02 sensors on that side. One upstream and one downstream. Upstream is before the precat. Downstream is after the precat.

i hooked up a dtc to it and i get the code p0420 and that means catalyst system efficieny below threshold bank 1

my next question is do i change both of them or which one do i change?

thanx for you help

daniel

[beyondloadedSE]

Originally Posted by Danielt14

i hooked up a dtc to it and i get the code p0420 and that means catalyst system efficieny below threshold bank 1

my next question is do i change both of them or which one do i change?

thanx for you help

daniel

Chances are when you get a P0420 or P0430 code, your precat(s) are cooked. It could be a bad 02 sensor but I highly doubt it. More than likely your 02 sensor is reading correctly and telling you that your precat is bad.

Things you can do:

-Replace the upstream 02 sensor and see if that fixes it.
-Gut the precats and install a set of MIL eliminators to trick to the computer into thinking the precats are still there.
-Buy new factory exhaust manifolds (~$1600 from Ford)
-Buy a set of aftermarket headers from MSDS to eliminate the precats all together
-Reset the battery everytime the light comes on.