Ah the dreaded blank speedometer issue. It plagues many 2nd gen Prius owners, and I was no exception. Basically, sometimes the Prius’s “combination meter” - the device that includes the speedometer and fuel tank level - doesn’t turn on. It affects other parts of the car too. For example, some information goes missing on the touchscreen, the backup camera doesn’t work, and sometimes you can’t even turn the car off!
It’s caused by a specific capacitor degrading. The temporary solution is to disconnect and reconnect the 12V battery in the back of the car. This usually works for a while, but is very annoying. And it seems to be more frequent in the winter, probably due to the cold weather causing the capacitor to exhibit lower capacitance.
Fortunately, there are a number of guides online for how to fix this problem:
- https://artsautomotive.com/home/art-icles/shop-articles/prius-combination-meter-repair/
- https://priusnotworking.com/
There are also some good videos on how to remove all the dashboard plastic to get to the problematic component. I used this one.
However, one issue I noticed was that the guides tend to recommend soldering on a standard leaded electrolytic capacitor. My concern with this approach is that there will be lots of stress on the solder joints and the leads themselves, as the car vibrates during use. The better solution is to replace with a surface-mount capacitor, similar in size to the one we would be removing.
Since I only wanted to take apart my dashboard once, I needed to order the correct parts ahead of time. Looking at photos other people had taken, I guessed what the proper surface-mount capacitor package size should be, and purchased a couple of similar sizes so hopefully one would fit. Later I found someone who recommended a Nichicon UUD1C221MCL1GS. I had already purchased a Nichicon UCM1C221MCL1GS with the same capacitance as well as pad and x/y dimensions. These are very similar capacitors, so I stuck with what I had purchased.
I followed the YouTube guide for removing the dashboard, then brought the combination meter inside.
Once I removed the combination meter (again, following the same YouTube guide), I set up my soldering station to remove and replace the 100µF capacitor with a larger 220µF capacitor. After placing Kapton tape over nearby components to act as a heat shield, I used a hot-air rework station to remove the old capacitor. I then cleaned up the pads and installed the new capacitor using a soldering iron.
I then performed the opposite steps from the disassembly guide to put everything back together. After everything was reassembled, success! And over two months later, the combination meter is still working fine. No 12V battery power cycling required.
