question..Tuesday check engine light coame on and flashed the whole time. Weds it was off and Friday it Turned back on and wa flashing again. Went to advanced and put it on the code reader and it shot out these code problems... all at once. system temp sensor, mutiple mis fire, coolant temp to low, mass air flow sensor, o2 running to lean, upstream o2 sensor, and another o2 sensor running to lean. Could this be all calculated towards one problems. Like a leaking head gasket? or something else. I had or still have a coolant leak somewhere but can't figure out where. I'm taking it on monday to c if there is a leak and if so where. But i'm trying to figure out why all the codes could come on at once. if so what is the main problem is that could focus on all of the codes coming on. 2005 H2 hummer

 

If you have a coolant leak it is likely the waterpump seal. At the dealer ship you can buy a pepper pill It sealed mine up.

As far as all the other gremlins look at your battery. How old is it? Sometimes batteries that are about to go bad can do weird things. Have it thoroughly tested. If you have one that is older I would replace it anyway and see if that does it. On my previous car (VW Touareg) I had the battery going bad causing a whole circus of lights, warnings and faults.