2007 saturn vue downs stream o2 sensors

Hello there, I recently got a used 2007 saturn vue with the 3.5L honda engine. The check engine light is on so I put a code reader on it and it shows p0141 and p0158. I looked them up it seems to be a problem with both the down stream o2/heater sensors. I erased the codes and started the car back up, they came back immediately. Wiring looks good but I haven't actually tested them with a meter yet.

I went to mechanic today just to see what they would charge to fix it because honestly I am too lazy to do it myself. I hate working on exhaust stuff and they look like a pain to get to working in my driveway. He told me unless I really hate the engine light being on to not bother fixing it. He said the down stream sensors really don't effect how the car runs they are just there to test how the cats are working. I googled it see if this was correct and I got conflicting results. Some said they really don't do much and others said it depends on the vehicle, it could effect if the car runs in open or closed loop or not. I don't get any other codes though, like that its stuck in open loop or anything like that and it seems to run pretty well for a car with 210K miles on it.

Is he right, or is this one of those cars that needs the downstream o2 sensors to run correctly? It doesn't get very good fuel economy, but it has other issues, high miles and these cars are not that great on gas to begin with since it is AWD with a v6 and auto trans. From what I can tell its getting like 15-20 miles to the gallon city/highway combined.

Other issues are it makes a rattling/banging noise by the right front fire wall when its cold, but we can't find anything loose. Goes away when it warms up and doesn't change based on engine rpm. The more I poke at it and research it I think it might be the timing belt tensionor but I haven't confirmed it yet. It only does it when you start it for the first time that day. And it hasn't done it in a few days because its been so hot out.

I also noticed yesterday the right front tire and wheel was VERY hot after driving it and discovered the brake was locked up. After it cooled down it freed up. I guess that is an issue with these cars after looking it up. I am going to change both front brake hoses today or tomorrow to see if that solves it. Seems to be the most common culprit and they were not that expensive. It also had a problem with spongy brakes and the pedal going to the floor when the engine was on. It stopped ok, not great but not scary. I figured maybe it needed back brake shoes so I looked at them yesterday. Brakes are almost new, they just didn't work LOL. They never self adjusted after someone replaced them. I manually adjusted them and presto the peddle feels good again and the car stops much better, imagine that.

I am thinking the brakes might be my fuel economy issue and not the o2 sensors. What to you guys and gals think?

 

Rear O2 sensors have the main purpose of detecting weather the cat cons are doing their job.

If people are using them in other ways to alter the drivability of the vehicle, that is their problem because that's not why it's there. I have no knowledge that Saturn did this.

When was the last time you changed your friend O2 sensor? They last about a hundred thousand miles and then get fouled up with all the crap in the exhaust from your engine. Therefore they do not detect as much oxygen as is really in the exhaust which tells the ECM it can add more fuel to the mix and still be at the right limit based on the O2 reading. This is what eats gas big time. As long as the sensor is responding reasonably, it usually will not throw a code as the ECM monitors its response curve

If there are no emissions inspections where you are, you can ignore the rear 02 codes, but I would replace the front O2s after the brakes. And change both rotors and pads on both front wheels so you have even braking. Just trust me on this