This was a lot to type so please forgive any grammatical errors. Hello there, I read over your post and this is going to be a lengthy process. The fact is that with having so many issues at once there is the possibility that you may have a bad wiring harness or even worse a bad ECU. The only thing any of these have in common is that they run directly off of the ECU. The good news is that the ECU being bad though possible isn’t likely. Just don’t go throwing money at anything until you check into all of them because the issue may be somewhere else. Start with the O2 sensors. They aren’t the easiest to test but the procedure is the same for both of them as well as part of… well everything else on your fun little list there.
There are just a couple things I want to clarify for future reference. First off was this car in a front end collision and if it was how bad was it exactly? You said you replaced the radiator and condenser. That sounds fairly bad in my opinion. Secondly by “fumes” you mean like exhaust fumes or something else?
Before I go any farther I’m going to say that this is just general diagnostic stuff. I don’t know the specific details about your car such as what pin goes where for what or what resistances a given circuit should read. There are too many different cars and way too many different parts that operate with slight variation to know all of those details. If anyone knows this information please fill in the blanks. So with that said here you go.
1.Set your multi meter to 100v. Clamp your negative lead to a grounded surface. With your positive lead probe the harness side of the O2 connector for 12v on the heater circuit pin and cycle your key to the on position. If you get 12v move on. If you don’t get 12v check for 12V at the heater circuit source (usually an ECU pin). You’ll have to look up a pinout diagram for your ECU online. Clamp your ground lead to a grounded surface in the car and with the positive lead back probe the respective ECU pin for your heater circuit and cycle the key to the on position. If your not getting 12v from there it may be a bad ECU move on to the next steps. If you are getting 12v its a bad wire. Trace, replace, and repeat step one.
2.Set your multi meter to 10ohm and probe the heater pin on the O2 side of the O2 connector. It should read between 2 and 5ohm but it really depends on the O2 sensors your car uses. If you don’t read anything or the reading is above or below what it should be then its a bad O2 heater.
Moving on to P0076 and P0079
Follow the same diagnostic procedures as for the O2 circuits making sure there is voltage to the solenoids as well as that the resistance across the solenoids is within spec. Check for mechanical operation by removing it and looking for debris and buildup and manually oscillating it. Also make sure it is not internally grounded by checking continuity between the pins other metal parts of the solenoid. Don’t quote me on this but I believe these operate on 12v so if everything here checks out and the resistance is good you should be able to just touch it to the battery assuming you get the polarity correct to test functionality.
As for the last 2 codes its pretty much the same procedure as everything else. check for power, check for resistance, check for operation. The main difference with these I believe is that if operation is impeded meaning if the valve is stuck it will throw the same code so fixing this may be as easy as just cleaning it out.
Let us know what you find out and good luck.