Under the hood of the S40 there looks like what seems to be (2) O2's in the front exhaust manifold. This is a 4 cy. I picked up a manual for the S40 on ebay, but when I plug in the vin # it doesn't show (2) sensors. Both sensors plug into the bracket located top and center on the firewall. Far left is to be the O2. I have an identical plug with the black, gray and two white wires in the second plug from the left as well. Both coming from the 2 sensors in the exhaust manifold.

Question: Are there two O2 sensors up front or is there one and something else? What is the something else and which one is in what position?

I'm installing an EFIE (Electronic Fuel Injection Enhancer) and if there are (2) O2's I'll need two EFIE's and I sure don't want to screw this up messing with the wrong one.

This has to do with an on-demand hydrogen kit I'm working with to strech another 20 mpg.

Anybody's help will be greatly appreciated. This is this weekends project.

I'll post my results when available, good or bad.

There are two O2 sensors one infront of the cat and one behind. Not sure what you are looking at though without pics.

It turns out that the 1.9T in the S40 has two banks in the exhaust manifold and each bank has an O2 sensor. I'll have to control the signal from each one. I'll have to get back to the S40 later with my experiment. I'm going to move on to my TrailBlazer for the first run at the project.

Thanks.

I dont think that is right. Normally with OBDII codes two banks means a "v" engine with two exhaust manifolds. the S40 only has one.