If you are required to drive only motor vehicles equipped with an alcohol detection ignition interlock device . . . yes it's illegal to drive a rental car that is not equipped. But note the ignition interlock requirement can come from many different sources. It can be a condition of bond, a probation condition, a condition of an occupational license, or it can be required directly by the Texas Department of Public Safety. If you have any questions about whether you can drive a particular motor vehicle, I recommend discussing this issue with a qualified criminal attorney familiar with the interlock rules.
If you are court ordered to have an interlock device installed on any vehicle you operate, then you would be violating the court's order. If it is a condition of probation, it would be considered a violation of the terms of your probation and you could be arrested. If it is a condition of bond, it is a violation of your bond and you could be arrested. There is a very easy solution to your problem - don't drive while your truck is in the shop. If you absolutely have to drive, get permission from the Court.
This answer is just to provide you with some thoughts on your situation and does not create or establish an attorney-client relationship.
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