This is a common 'safety' feature of built-in navigation systems. A quick Google search shows there is a work around for the 06 which may or may not work on the 08.

For my money, a dash mounted GPS is a much better deal than a built-in. For $700 you can get a high-end Garmin that has better features, better maps, cheaper map updates, and can be moved between vehicles.

There are a few companies producing mods that overcome this issue, but may void parts of your warrenty, so I'd agree with cbibbs that an external model is a better choice. Then you can use that dash to monitor your mileage to help maximize.

Yes I am aware of this being a Garmin user for the past several years but having a GPS unit stuck on your windshield is IMO a great way to have your car broken in to.
I really prefer to have something in dash for the convenience factor with out wires hanging down from a windshield mounted unit.
Even the residual suction mark is a signal to potential thieves that there is something valuable in you car

I use a dash mount and fished the wires out of sight. It takes about 10 seconds to hide it when necessary (and I work in Detroit so I know a thing or two about seedy neighborhoods.)

Still, you may consider an in-dash after market unit. They cost about the same as OEM models, but generally include directions on how to defeat the in motion block.

Thanks for the great info and quick response but I am unaware of any after market in dash units.
Do mean have your dash modified to accept a Garmin unit or remove the OEM radio and replace with it with a radio/GPS type unit ?

I meant replacing the factory radio with an after market unit, but it appears the Highlander's stereo is a non-standard size and can't be replaced without getting a customized dash. (If you haven't priced that before, it isn't cheap.)

You might want to check out your local customizer to see if they have any ideas, but the built-in GPS is what, $900? You'll be hard pressed to do a custom job any cheaper.

You can purchase a "double din" after market mount that would be a compatible replacement for your factory in dash 6-disc changer. Your reputable (or seedy) custom car install shop can override the settings, or "accidentally" leave it so that you can wire it yourself. Thereby excluding them from any legal liability. I had my guys do it for me. They had to place a 2 inch screw through my HiHy's speed sensor, allowing the nav system to think that the parking brake sequence was on. If you are interested in who did the work on my car, please let me know. I would be happy to share that info, but it can be done! I have a pioneer Avic-D1 unit, but the new Avic D-3 is quite nice as well. Best of luck!

If you are interested in using the NAV system and Telephone dash input while in motion go to ebay and look at 320225493732 and upgrade to NAV ver 7.1 unlocked.