2010 JBL Navigation unit buttons "remapped" - fix?

BLUF: Disassembling and cleaning the NAV unit buttons fixed the strange button behavior and didn't end up costing me several thousand dollars. Duration of fix to be determined, but so far so good.

In my attempts to find a possible fix for the button remapping issue that I've encountered with my 2010 Prius V NAV unit, I've noticed that this is not an uncommon problem. Since replacement estimates have ranged anywhere between $2500 and $4500 and I do not currently have a viable warranty, I figured it would be worth trying to repair the issue myself. From what I observed it looked like the button issue would likely be something in the faceplate rather than internal to the radio. The job didn't look too complicated, and I suspected that the button contacts could have become corroded from who knows what contamination (glass cleaner, food, water, mold (see VFD display blurred for info about that one, my next project by the way). The only way to find out was to disassemble the unit. Apologies in advance if I've missed any steps, but they should be reasonable close. When in doubt, use caution (or go with your gut...).

1. Place the car in accessory mode and open the CD/Map DVD access so that the LCD is sticking out and not in its normal position. (found out the hard way to do this before attempting to dismantle anything).
2. Power off the car. (Disconnecting the 12v battery seems like the logical step to take here since you don't want to damage anything while working on the unit, but I neglected to do this; I'll explain why failure to do this is not the best approach later)
3. Remove the trim panel from around the shifter and disconnect the leads going to the hazard switch and mode switches. There is a third wire on mine that connects to the Park button, but it is connected in series with the mode switches and doesn't have to be removed.
4. Remove the radio trim panel. For reference, this piece also includes the cup holder and is the largest of three pieces to be removed. Disconnect the lead for the clock and English/metric switch. Note that on mine there was a convenient "dead head socket" made of white plastic behind the panel that I could park the connector while working on the car. Feel free to use this as needed if it is there.
5. Remove the power switch panel. I didn't find it necessary to disconnect the electrical connector from this as it could hang freely to the side without posing any interference risk. Granted, I cannot confirm whether disconnecting this would cause issues with the car (required reprogramming or resyncing key fobs?) so I'll leave the decision whether or not to do this to the reader.
6. Remove the four bolts securing the head unit to the dash using a 10mm socket and a reasonable (4 to 6 inches should suffice) length extension. Use caution with the lower two bolts as it would be really easy to drop them into the dash and there isn't much space to squeeze your hand in to grab them. Use a low powered magnet to retrieve them if possible.
7. Pull the head unit out enough to provide clearance to disconnect the wires from the back. If I recall correctly there were 7 or 8 individual connectors on mine, but this could vary by model. Fortunately each connector is color coded and different sized so reinstalling them should pose no problem. Also note that the unit appears to pull power from the white connector near the bottom of the unit (for reference in case anyone works on this without pulling the 12v power source first).
8. On a workbench with adequate space, disassemble the front bezel. You should only need a PH0 screwdriver for all screws removed in this process.. There are six silver screws holding on the main plate, two on the top and four on the bottom of the plate.
9. Next, remove the two clear plastic covers (2x PH0 screws on each) that guard the interface ribbons connecting the front bezel and the main part of the head unit. These ribbons will need to be disconnected and are very thin so be careful. There is a flip-up plastic release (dark brown if I recall correctly) that has to be moved in order to release each of the ribbons.
10. Remove two black PH0 screws from the back of the front bezel to remove the back cover and gain access to the button assemblies. These screws are located near the top of the bezel and were rather tightly installed on mine. Use caution when removing them so that the threads aren't damaged.
11. Once the cover is removed, you should see two circuit cards, one on each side of the front bezel assembly. Each one is secured with three silver PH0 screws. Remove the screws and the board should lift out. Do so gently as each one has a knob attached that likes to hang up if removed at an angle.
12. Remove the rubber backing that rests between the circuit cards and the physical buttons. There is one of these on each side.
13. Check the circuit cards for any foreign material and clean as needed. It may also be prudent to check the circuit paths with a volt meter if you have one and are reasonably competent with that sort of thing (I'm not, but I did it anyway just to check for continuity). Check and clean the rubber backing as needed, ensuring that none of the rubber studs that make contact with the circuit cards are missing or are stuck in any way.
14. Reassembly is the reverse of the removal. Particular attention must be paid when reattaching the ribbon cables detached in step 9. I suspect this is where the problem of button mapping comes from since I didn't find any foreign matter on the circuit cards. Heat expansion and contraction may cause "creep" which causes the cables to lose connection after a while. Hence, make certain that the cables are fully seated before pushing the brown lock tab down. If it doesn't look right, redo it while you can. Having to redo the removal process to fix a loose cable later can be frustrating.
Some reassembly caveats.
* If you decide to test the radio function before completing the reinstallation of bezels and buttons (as I did), be aware that all connectors MUST be reconnected before powering up the car. Failure to do so will trigger the master alarm and a rather persistent "Check hybrid system" message. Apparently I failed to reconnect the mode buttons while testing the radio, which the ECU was quick to pick up on when I cycled through the power modes. It took three drive cycles and connecting a scan tool to clear the error.
* For trim removal, make sure you use plastic tools made for that sort of task. Advance Auto Parts (or similar parts houses) sells some generic trim tools that fit this task well and aren't terribly expensive. I've used metal tools in the past and made some very costly cosmetic mistakes.
* Attempt these fixes at your own risk. Working around electrical connections always carries risk. Be safe, not sorry. What worked for me isn't guaranteed to work for everyone. If there is anything resembling a warranty or service contract on your vehicle, seek assistance through those first.
Good luck.