Please understand, without a code, this becomes a guessing game. The first thing that comes to mind is the theft deterrent module. It is located in the steering column. Here are directions for replacing it, but you will need to reprogram it if this is done. The pics below correlate with these directions. The first pic shows location and the second contains the directions. I don't want to mislead you. The module is what recognizes if the vehicle is being stolen and provides information to the ECU. All programming and control of the theft deterrent system is done by the ECU.
2011 GMC Truck Terrain FWD L4-2.4L
Removal and Replacement
Vehicle Accessories and Optional Equipment Antitheft and Alarm Systems Alarm Module Service and Repair Removal and Replacement
REMOVAL AND REPLACEMENT
Theft Deterrent Module Replacement
I hate to say it, but honestly, I recommend finding someone with a scanner that can read all codes. Perhaps the tech that checked it doesn't have the capabilities to read these codes and that's why nothing shows up. I don't want to start recommending that you replace parts that are most likely good. I hope you understand.
Let me know.
Images (Click to enlarge)
Sunday, January 5th, 2020 AT 6:42 PM