stick your known good spare in and see if it works.
Pssst - being a mechanic means knowing what tools to carry. A pocket scanner and a multimeter is a must - the multimeter is essential even on non-computer cars.
Psst! Did you know that battery operated gizmos don't work below freezing very well? And did you know they don't work at all at -10 to -40 degrees?
You’re carrying a spare module? Okay, it still doesn’t work. What now?
Either way, without a meter, you’re still walking out.
And, strangely enough, you can get a multimeter that runs off your car battery. If your car battery isn’t working, you’re screwed anyway.