Hi!

Do new (year 2005) car radios have a service mode for some basic
configuration?

Maybe, I don't know.

However, it looks like the TEA6848H is externally programmed at each
power-up. Whatever defines the allowed tuning range and tuning "steps" is
probably hardcoded in an external firmware IC. Such an IC might be
programmed as the radios run down the line.

You might ask a Chrysler dealer if they have the ability to reprogram the
radio... I think most GM dealers can do at least minimal reprogramming of
their radios. Chrysler may have a similar program.

William