It is not clear to me from your question, but in context I assume the car was used as secured collateral for a loan. The tracking device is probably a requirement of the loan and your agreement with the creditor who loaned you money. If that is the case, then disabling the tracking devise would be a breach of your agreement. In addition, this could be hindering a secured creditor, which is a crime (Tex. Penal Code § 32.33).
Proceed very carefully.