Hello I will help you with your question,
In your state the only way to reset the check engine light is to buy a code reader for $40 - $60 and use that tool on the diagnostic port under the drivers area of the dashboard.
Before you do that what code are you getting that you want to clear?
Clearing the memory will reset your emission monitors so that they will read not ready if you have an emission test due. The vehicle will have to be driven and pass the internal tests (no codes set) to be ready for the emission tests.
So what code do you get that there is no problem for?
I can't imagine that they cannot verify the problem. If the check engine (service vehicle soon) light is ion there is a problem with the transmission, the wiring or the computer.
Do you know what the code is?
It should be noted on your repair order. I suspect that it is the Torque Converter Clutch Solenoid as the Cadillac has many failures of this part. Without the code though all I can tell you is that you can buy a code reader at any autoparts store and clear the codes to turn off the light but when it comes time for inspection you will not pass with a code set or if you have just cleared the code.
The best thing to do is find and fix the problem and with the state GM is in today I can't believe that a dealer is turning down work.
Look at your invoice and see if there is a P1860 code listed there
Let me know what I can do to help you with this
If the code is the P1860 for the TCC solenoid and not the torque converter itself (unlikely that it is the converter) then see below
The way this is repaired is to lower the transmission and remove the side cover to replace the solenoid. The part is about $60 and the labor books for 6.1 hours but the job can be done in about 1 1/2 hours so you may be able to deal with them on the labor charge.
If it is the torque converter itself it is much more involved
I would go to the other dealer, I cannt understand why the first dealer did not want the work, this is considered a "good" job.
Let me know if there is anything I can do to help you