kind of a dumb question, but here goes. After putting the trans back in, and rehanging the exhaust, I was able to locate the connectors out of the main wiring harness to plug in the driver's side front and back 02 sensors. However, I cannot find where I am supposed to plug in the passenger side 02 sensor. Does the plug come down from the passenger side of the engine compartment? Where should I be looking to find this? the truck is a 2003 XLT 4WD with a 4.0. Thanks.

 

Upstream O2 sensor wires are usually located in the wiring harness on the firewall behind the engine.

Are you sure the "back" O2 sensor wire wasn't the passenger side O2 sensor wire?

 

The 95~2003 Ranger 4.0's have 3 O2 sensors. There is 1 sensor for each of the 2 cylinder banks and these are upstream of all cats. The third one is for cat efficiency monitoring and it is positioned after one or more main cats.

 

Thank you Ron, The missing wire was exactly where you said it would be. However, when I bolted the trans back up to the engine, I managed to sandwich this wiring between the engine and the bellhousing. At least I know where to find it! haha.
Ken

 

I am having the exact same issue and I also have a spare wire underneath near the transfer case which I have no clue where its suppost to plug into

 

Welcome to the forum

What YEAR ranger?

Looks like automatic transmission


Looks like a 2 wire plug, the 2001 and up 5R transmissions have ISS sensor and OSS sensor on the outside of transmission, drivers side, each is 2 wire

Picture here: http://carphotos.cardomain.com/ride_...0010_large.jpg

ISS sensor is circled, to the right and up is the OSS sensor