Upstream bank #1 oxygen sensor location?

1999 Cougar 2.5L V6 55,000 miles

I have a DTC code 1131 : "Lack of upstream Heated Oxygen Sensor (HO2S 11) switch, sensor indicates lean ( Bank #1 )"

Figured I should change the sensor first, but not sure which one this is. Could someone tell me what is considered bank #1 and bank #2? And also what is upstream and downstream?

I'm not sure which bank it is in but the upsrteam O2 sensor is the one in front of the the calatic converter and the downstream is the one behind it.

bank #1 and bank #2? And also what is upstream and downstream?


Bank#1 is located in the 'Y' pipe off the engine right before it goes into the catylic converter under the car. I am getting ready soon to change that one myself. (I have a 99' mercury cougar too).

If you have any questions please feel free to email me @ saresmile21@yahoo.com

Sarah

bank one is the rear of the car.

bank one is the rear of the car.
Yes I know that. Its before catylic converter under the car.


http://img.photobucket.com/albums/v352/fixation101/cougar/April2004kat.jpg

Yes I know that. Its before catylic converter under the car.




congrats. Both banks are before the cat before the car. :loser: However you werent the one that asked the question to begin with and he specifically asked which side was bank 1, which you did not answer, other than it was on the y-pipe.

Ok here is where people are getting you confused. On a 99 cougar all four O2 sensors are before the catalytic converters. You have pre-catalytic converters on each side of the engine. On the top of these pre-cats is your upstream O2 sensors, Bank 1 being towards the firewall, and Bank 2 being towards the front bumper. The upstream O2 sensors have a square connection and the downstream sensors have a round connection.The downstream sensors are at the bottom of the pre-cats and one of them appears to be in the Y-Pipe. Alot of people see it and are thinking it is the upstream, because they are used to dealing with cars that dont have precats and in that instance that would most likely be where the upstream would be. I hope this clarifies things for anyone needing this post in the future.