This happened on my 2007 H3 3.7 with 305,000 miles. I'm just posting this as a reference for anyone else who may have this issue. I could not find a definitive solution searching the forums. It's a little confusing because the check engine light and Service Stab Sys warning come on simultaneously (actually, the check engine light illuminates a couple seconds before the Service Stab Sys Traction Failed message comes on the dash). This problem also immediately put the vehicle in Low Power Mode with a max speed of about 50mph. It appears that the Service Stab Sys Traction Failed message is not the root cause of the problem. The trouble code P2122 is the problem. It is listed as Throttle Position Sensor - D Circuit. Low Input. This page offers very good information on this code https://www.700r4transmissionhq.com/p2122-hummer-h3/

It seems that the solution is typically either a problem with the throttle body or the accelerator pedal or the voltage supply to either one or a bad connection at the PCM. In my case it was a faulty accelerator pedal. I was able to test the condition and work around it without spending any money on parts by placing a 1/16" thick metal shim between the accelerator pedal and the housing. This shim just keeps the pedal from retracting all the way. The output voltage from the pedal must be slightly out-of-range when the pedal is fully retracted. I will be purchasing a new pedal but this got me back on the road and saved me from buying parts I didn't need. After making this repair I did disconnect the battery so the PCM would reset the closed throttle voltage since the throttle is now in a slightly different position when "closed". Not sure if this step was necessary but the engine idles just as it did before.



Bent sheet metal shim. About 1/16\" thick


Keeps pedal from retracting fully. Test fit.

Shim glued in place with RTV and strapped with a zip tie. Works fine. No more codes. Cost to trouble shoot and make temporary repair $0. New pedal ordered and on the way.

 

Interesting, and nice fix. The problem with the "Service Stab Sys Traction Failed" message message is that it comes on when there is pretty much anything wrong, anywhere! The computer, if there is any problem, shuts down the Stability system as a matter of course (which unfortunately tends to lead you down the wrong path trying to figure out what's wrong). As you found out, your problem had absolutely nothing to do with the Stability System.