I don't think this thread is dead yet. Both my trip button and the mph/kmh button don't work, or are very intermittent. And it's not because I don't understand how they coordinate with the FCD button. I definitely am in the odometer display when pushing the trip button (not the "segment" display with the <===> symbol displayed.)
Note: call it the segment display, not the trip display, because the displays: odometer, trip A and trip B are three alternatives controlled by the trip button when in odometer mode as controlled by the FCD button. That is the FCD button toggles between odometer mode and segment mode.
I think it might be corrosion under the grounds. Cleaning the battery ground to frame connection seemed to help a problem with the fuel gauge. So I am going to clean some of the other grounds, before I pull the gauge/instrument cluster. When I cleaned the battery ground to frame connection, I found either gray primer or silver paint under the connector. So I scraped and sanded that off (I don't want to rely on the bolt and the top of the connector to make the ground.) I say this seems to have helped, the verdict is still out.
Note that battery terminals often develop a thin film of corrosion between the post and the connector. It doesn't seem like much, but in a high current situation (cranking to start) it matters. But in this case, I wouldn't have thought that a little corrosion on the grounds would matter.
An aluminum car doesn't solve all the corrosion problems, and might even have more corrosion problems due to galvanic action. My car was originally from Michigan where salt is used on the road and has rather bad corrosion problems all over the car, including most of the steel bolts in the engine compartment. The engine to frame ground cable was corroded and broke.
Even the dealer (well the service coordinator, the greeter) couldn't get the trip button to reset the "Maintenance required" light. And they said that the tech couldn't do it any other way, it definitely requires the trip button to be functional.
If I do pull the gauge cluster, I'm hoping the switch is accessible for cleaning or replacement. Anyone seen the thing up close?