2001 Mercury Mountaineer 5.0 4R70W RWD

[ActionYobbo]

Is the driver side upstream 02 sensor part of the engine harness or is it part of the Transmission harness? Another question there are blue plugs and a gray plug are the gray for the up stream and blue for down stream 02 sensors or reversed?

 

[CDW6212R]

I think all of the O2 sensors are part of the trans harness. The tough one to change connects way up on top of the transmission. I think the blue connectors are for the rear pair, ignore the rear O2 sensors.

 

[410Fortune]

the drivers upstream sensor is the only one that is not connected at the top of the transmission instead the connector is found up near the brake booster

the other three connectors are located on top of the transmission

 

[ActionYobbo]

the drivers upstream sensor is the only one that is not connected at the top of the transmission instead the connector is found up near the brake booster

the other three connectors are located on top of the transmission

the drivers upstream sensor is the only one that is not connected at the top of the transmission instead the connector is found up near the brake booster

the other three connectors are located on top of the transmission

I figured the gray are the up stream for you left and right and the blue are for the rear down stream. But I have seen them green as well so different color but same purpose.

 

[410Fortune]

I believe that is correct, green or grey are upstream, blue are the two catalyst monitors

I just happen to have a 97 5.0 trans harness in the shop
Here we can see indeed the two blue connectors are for downstream sensors the single green is for pass upstream sensor