Contour Enthusiasts Group Archives Forums General Troubleshooting I have a CEL and the this is what the OBD II said....

I have a CEL and here is what the OBD II said... 171 and 174 That is a lean bank on 1 and 2. It started about 60 miles after I cleared out my precats and added the 2 MIL eliminator on the bottom O2 sensors... now I have a light! I only took off the y-pipe and did not remove the upper O2 sensors. First I tried a pair of MIL Eliminators that solder in and then after the light came back on, I added a set that clip in. However, I did not remove the first pair.(so I have 2 pair on) The car gets about 24 MPG on the highway and 14 MPG in town. It smells like it is running rich! Please help! I've lost some power and the Gas milage is killing me!

By the way, this is a 1999 2.5 V6 Cougar.

The 171 & 174 codes would be coming from the first set of O2s before the pre-cat. Did you remove these when you gutted your pre-cats? (Maybe they got damaged...) What's up with the 2 sets of MIL eliminators? Is one set just hanging there or did you also put some in for the first O2 sensors. ??? Try cleaning up your upper o2 sensors, and put in ONE set of properly connected MIL eliminators for the bottom sensors and see what happens. You may need new upper 02 sensors.

I didn't remove the upper O2 sensors when I cleared out the precats... so maybe I did damage them? The extra set of MIL eliminators are there because I thought the first set didn't work and I didn't want to remove them (solder in) so I just plugged another set in. Are you sure that those codes mean the 1st set of O2 sensors? Can they be cleaned or do you think they are just busted?

The upper sensors are used to monitor if the mixture is rich or lean. The lower sensors monitor the pre-cat efficiency. If the computer doesn't see a different reading between the upper and lower sensors, (like if the pre-cat is gutted) it will flag a CEL code. Try cleaning the upper sensors, if that doesn't work you may have to replace them. Might also want to make sure you don't have any intake leakes inboard of the MAF that are really causing a lean condition.

Is removing the upper O2 sensors a hard thing to do? They look hard to get to!