2000 Ford Focus Codes: p0136,p0141,p0171

At first I had only codes 141 and 171. I had the spark plugs, wires and one of the o2 sensors replaced. After I got my car tested again, those same codes plus 136 came up. So now I don't know what to do.

Should I change my other o2 sensor? or is it something different?

Help please.

Which O2 Sensor was replaced and what brand did you use?

The O2 codes are for the post cat O2 sensor.

Also check the fuse, wiring and connection to the sensor.

The lean code may go away after the O2 sensor issue is addressed but check for vacuum leaks if it doesn't.

Good luck and keep us posted.

I currently have a po171 code on my 00 Ford Focus Se. I changed the fuel filter, both o2 sensors, the spark plug wires and plugs. I want to change the pcv valve prior to resetting the code. Do you know where its at? I thought it was on the valve cover. I followed the line from the air filter box to the valve cover, but it doesn't look there is anything that I can remove on there. Any help would be greatly appricated. I bought a new pcv valve, but not sure what to do with it.

Thanks