Code Meanings

[Mao]

I just got a trouble code of P1131 ... Lack of H02S Switch ....Sensor indicates Lean. I am assuming this means one of my Oxygen sensors is bad? ...If so, which one ....the switches are original and connected. Car has nearly 80,000 miles on it. The "check engine" light appeared shortly after I had spark plugs changed ...coincidence or related somehow??

[beyondloadedSE]

It doesnt neccessary mean your 02 sensor is bad, although it probably is. Usually after about 50K, its about time to replace them.

This code is bank 1, sensor 1 which is the 02 sensor nearest the firewall. Btw, which spark plugs are you using?

[Mao]

Nearest the firewall meaning the sensosr before the converter?
I believe they were Autolite Platinum plugs.
Do you think the plug change could have caused the light to appear?
I didn't notice the light until I had driven about 100 miles after the plug change. Figured that was just coincidental.

By the way... regariding the plug change, anyone else have difficulty removing those spark plug boots? Had to take them to a garage that had a specially designed tool to get mine out.

thanks for response.
Larry

[beyondloadedSE]

Yes, the sensor located nearest the windshield i guess you could say. There is only one firewall. The plugs could have caused some trouble. I know the Bosch double plats are a big no-no in this engine, but i think Autolites are recommended for this motor. What you may want to do is rotate the plugs from the rear bank to the front bank and vise versa and see what happens. As for pulling off the plug wires, my 9mm Ford Motorsport wires come off a little hard, especially on the coil pack, but they come off after you pull hard enough.

[Mao]

Guess I should have mentioned that I have the 2.0 4 cyl ....one 02 sensor on top ....one on bottom ...Ford confirmed the code applied to the upper sensor. I am going to replace both sensors and see if that is the remedy. Will I have to reset the code or should the "check engine" light go off if that was the problem?

[beyondloadedSE]

Originally Posted by Mao

Guess I should have mentioned that I have the 2.0 4 cyl ....one 02 sensor on top ....one on bottom ...Ford confirmed the code applied to the upper sensor. I am going to replace both sensors and see if that is the remedy. Will I have to reset the code or should the "check engine" light go off if that was the problem?

oh, i just assumed you had the V6 duratec. Yeah, just replace the sensors and they should go off on their own. If you want, you can disconnect the battery terminal to reset the battery which will also clear the codes.

[Jeschmidt]

I know that error code P0420 is catalytic conv efficiency issue with Bank 1.

1) could this be O2 sensor? IF so, is it upstream or down stream of catalytic conv closest to firewall?

2) if it is Bank 1 catalytic conv issue, where is cheapiest source to buy one?

[Mao]

The O2 sensor was the problem .... fixed.

[Jeschmidt]

Which O2 sensor was replaced? Upstream (before cat conv) or downstream (after cat conv)?

[Mao]

The one before the cat converter