2007 Hummer H3 sounds like Semi Truck?
 

Recently I have bought a 2007 Hummer H3 that I absolutely love, but have been having issues with codes being thrown and the car itself sounding like a school bus when accelerating. Before this would happen occasionally, as I have driven it before where it was quiet and actually had some power to it, but as of recently the car sounds like its about to take off into flight every time I accelerate. The car will consistently sit between 2200-3000 rpm while driving, and again I know it shouldn't sound this way because it has been much quieter before. A P0742 code was shown up recently as well, and I am assuming that this is related to the loud engine noise and higher rpm, as the torque converter being stuck open can produce these symptoms, but I am not totally sure and want to double check before I spend the money on getting it fixed. Also when I unplug the battery to reset the codes, the hummer is much quieter, but after driving 100 miles or so the check engine light kicks back on and the loudness comes back. I replaced the fan clutch recently and thought that may have been the cause for how loud it is, but it seems to only happen when the check engine light is on. I know it sounds like I am answering my own questions, but just want to check with the community here to see if the symptoms sound like a P0742 issue or possibly something unrelated before I go blowing money on things that are unnecessary right now.

Welcome. Miles is important info in any tech question. When a Trans issues so is knowing when the last time the Trans fluid and filter were changed.

Disconnecting the battery does not “reset codes” as the H3 stores the last 300 ignition cycles, power or no power. It can turn off some CELs only until the PCM commands the light CEL to illuminate. The code alway present when the condition persists.

Seems like you know it is a TQ Converter engagement issue, can be electrical, can be dirty cooked fluid too. 07s have no TCMs so could be a PCM or PCM harness problem as well. I would carefully inspect the Trans electric harness for compromise.

Good luck. Follow up what you find out.