Hello all, I'm new to the forum and have an '05 H2 that's having some issues. First and most scary is that we recently noticed a pretty loud rattling noise coming from under the truck. I climbed underneath and it seemed to be very centrally located like either Xfer case or tranny very close to Xfer case. I almost never drive in anything but 4 Hi (normal) so I haven't checked the operation of the 4WD yet, I thought maybe someone else has experienced this and had some opinions before I go messing with 4WD.

Next, when idling, the engine occasionally almost stalls completely and the A/C doesn't work very well when idling. I also occasionally have a surge when traveling at highway speeds. It generally goes away after a few seconds but is definitely noticeable.

Last, while making a short 10 mile trip into the foothills last night, with the A/C on, the engine temperature gauge moved well past the 210 mark. I have made this same trip numerous times with the A/C on and the gauge has never even moved before. I would say that I was going probably 35 to 40 mph on the winding roads when I noticed this and I immediately shut off the A/C and the truck cooled back down to normal.

Any ideas on any of these things before I make the dreaded trip to the dealer and get hosed for a few thou?

Thanks in advance!

 

I have only owned my h2 for a couple of weeks so i don't know the character problems in them yet but as a mechanic owning allot of different vehicles in my life time it could be a few different things or just one thing. Is the rattle heard when the engine is running but not moving ie in park or any other gear if so then go under the truck feet first while hearing the noise and put your (shoed) foot on different parts under there especially heat shields and protection plates to see if one of them is loose. I think something is loose causing the rattle noise in turn causing a false knock (if the hummer has a knock sensor) causing your rough idle especially with ac on. I had a similar problem with my dodge ram and it turned out being a broken brick in the cat.

 

Thanks, so the false knock will trigger the knock sensor and cause the idle problems? That actually sounds like the problem so now I just have to determine what the rattle is. Could the knock sensor also cause the engine to run hotter?

 

it may, i am still old school on the mechanic side of things, stil having a hard time grasping new technology that is why i have a computer to plug into the truck and view each sensor to see if they are within specs and changing values like they should. My ram's broken brick messed with the knock sensor and the o2 sensor causing my idle and performance issues. Just crawl under and put pressure with your foot on different parts under there to locate the rattle, i say use your foot so you dont burn your hands in case you were wondering.

 

had this exact same thing happen to my h2 EXACT!!! it ended up being the cat. converter on the passenger side lucky for us hummer has 2 cost with labor to replace 800.00 total 500.00 for cat 300.00 for labor only did the bad one. hope it helps..

 

If it is the cat and you do not have o2 sensors downstream of the cat then just remove whatever part you need to to get to the cat and punch it out with a pipe or large 1/2 ext and vacuum it out. It will cost you just time and the exhaust will sound a bit more aggressive. I have done this to mustangs and Buick grand nationals allot, it will still pass emissions by the sniffer and visually