Speedometer Backlight doesn't dim when headlights on Auto setting

We've use the Auto position for he headlights most of the time since our 2008 was new. Not every time, but too often, the speedometer cluster lighting doesn't switch to dimmed setting when the headlights come on. It seems to happen most frequently when we are in a parade at night. The backlight for the radio dims properly with the Rheostat, but not the Speedometer Cluster. To get it to work properly, you simply need to turn he headlights off and back on again. (or today, open the door)

Sometimes the dim after a 5 second delay (after covering the sensor), and other times, they don't dim after a 20 minute drive in the pitch black.

So what gives? Is this normal?

The dealer, three times now, tells me this is normal operation for the Prius. And claims there is nohing to fix under the expensive extended waranty we paid too much for. I've been bringing this up almost every time we bring the car in... For more than 4 years now.

If you don't see why this would be a problem, turn your display to the brightest setting and go for a drive on a stormy night.

 

Does anyone else have a problem with their dash lights not dimming when the headlights come on in Auto mode?

 

The funny thing is that the lights around the radio, etc dim with the wheel... But not the speedometer cluster backlights.

 

We've got a separate wheel "Rheostat" to adjust the brightness. It doesn't consistently dim when the lights come on, but if you turn off the headlights with the knob and then turn them back to auto, they then dim. It's acting like the "relay" for that branch of the circuit is sticking and not allowing the backlight to switch from day to night mode... Until you break power to the circuit which resets it and then it works properly.

Toyota Ademantly insists that this is the way it is supposed to work and even compared it to one of their used cars to "Prove" it. Although, I could get ours to act up, and theirs worked differently when I tried it.

 

Toyota left a message today... They're talking about throwing parts at it. They're wanting to put a combination meter in it... Even though they've previously said they don't think that'll resolve it.

Will this reset the odometer to 000,000?

 

It's very interesting, however it would be interesting to see what the various connectors hook too.

 

I think I may have found the answer.
GSIC - Global Service Information Center

From what I see here, if it's not a setting, the combination meter needs to be replaced.

 

I'll be taking the car back to Toyota on Monday and it'll likely be getting a new combination meter... Since that's what Toyota's service manual indicates to replace when the rest of the dash lights dim but not the combination meter.

 

Well... The new combination meter didn't resolve the problem. Wth. Now what?

Combination meter backlights didn't dim propperly 2 out of three trips last night with the headlights on Auto setting. If anything, the problem is worse. The "Heater Control" lights dim propperly with the knob, and the Combination Meter processor isn't getting the message until the headlights are turned off and turned back on.

 

Haven't driven it much at night recently, so I've not had it act up again since.

No, nothing else has been replaced. If I understand correctly, they've hooked the car to the computer, and it says everything is working as designed... what they've been telling me every time I brought it up with hem in the last 4 years+. Although their tune has changed a bit after I sent them a video of a nighttime drive (in the pitch black) where they didn't dim for 5+ minutes till I shut off the headlights and turned them back on, and presto, they dimmed to the adjusted setting. (Meanwhile, the "heater" lights all dimmed by the Rheostat while the Combination Meter stayed at full bright... Also in the video)

 

I finally figured out how to get it to act up. Go for a drive at night, stop, leave the headlights on for a few minutes with the car shut off. Watch as the power in the 12V battery drops down to 10V… Turn the car back on with a low 12V battery. Dash lights will never dim when the lights come on, on Auto setting. Turn the headlights to off, while the car is powered up, and then back on, and things work properly… because the 12V system is now getting 14.2V from the main battery. Replaced the 12V battery and the problem has gone away… at least until I run the 12V battery again.