Q: Do you need to reprogram after replacing throttle body on 04 trailblazer

The Service Manual does not "require" any specific intervention (re-learn procedure). On this vehicle, the PCM will, by default, update itself to new values, just as you idle and drive the vehicle, if such new values are required. Even if you need to manually "force" such re-learning, all that is required is running the car through a few intervals of idling (with the vehicle off in between) and the PCM will update itself. Again, this updating will happen anyway, as you drive. Note, though, if codes set during the re-learn, erase them to permit the re-learn to continue. Ultimately, of course, no codes should appear. If you desire professional throttle body replacement and system check out, please simply visit YourMechanic’s throttle body service page and click on "Get a Quote". If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.