About a month or so ago I had to replace one of the O2 sensors on my truck. Just last night my "check engine" light comes on. I had it tested at Autozone and it turns out another sensor is going bad. Slow response on the one located behind the cat converter. I guess my question is do these go bad this quickly? My truck only has 46,000 miles on it.

 

typically no, have you been running any fuel additives, like a lead subsitute?

 

I've never used a fuel additive in my truck.

 

Are you losing any coolant, that kills them.

 

What was the number of the code that came up? I'm guessing that it was P1137 or P1138 in which case the Ford Manual says the following (also applies to codes P1157 and P1158):

 

Ken,

My coolant level seems to be fine. Doesn't look like I lost anything.

 

Joe,

I don't remember what code was pulled. It came back something like "bank 2 sensor...." and something after that about slow response.

 

Bank 2 is the driver's side....and if it's located behind the Cat then it is called the "downstream" sensor. Diagram Here.

Probably means a P1157 or P1158 code, both of which refer to that particular sensor.

More on DTC's here: OBD-II Codes & Possible Causes