I did a search for this using the search tool here but it didn't pull up what I needed. I changed to a Prochamber about a month ago and the check engine light comes on, no big deal. I know it is the O2 sensors. I got my MIL elims about two weeks ago and installed them. They were the kind you have to solder in. I put the elims in and unplugged the negative battery cable. I let the car sit for a while and then started it. The CEL light was off, perfect. My wife was driving the car the next day and the light comes back on again. I got the codes pulled today just to make sure it wasn't an engine issue. Sure enough, code P0135, and P0155. Both O2 sensor codes. What does this mean? Are my elims not doing there job or what? Do I have to replace the O2 sensors and resolder in the elims. i put the elims in the banks tha were furthest downstream in the exhaust. i am pretty sure they are in the right place. Any ideas?