Headlights very dim on low beam

We need more clues. Are both low-beam headlights equally dim? Is the color of the dim light normal, or sort of orangish? Are the other lights normal brightness?

 

Measure the voltage on the headlight plug.

 

Upside down? Is that even possible?

More likely, it sounds like the bulbs were installed crooked or off angle. When that happens, sometimes there is excessive heat built up close to the plastic headlight mounting holes. Hopefully, there is no melted plastic in those areas.

 

I was having the same problem in my 2010 Prius II. Dim headlights on the low beam, with halogen bulbs. Here's how I fixed mine: It turns out the bulb wasn't properly installed. Because the bulb wasn't properly seated in the housing, the optics in the headlight casing weren't amplifying and shining the light properly. All I had to do was play with it until it was installed properly. Don't try to install it with the wiring harness connected, this makes it more difficult. Instead, install the H11 bulb first, get it fully inserted and seated, and then connect the wiring harness. If your bulbs are dim right after they've been replaced, this is your problem. The bulb was not fully seated/installed properly.

 

It looks like I'm on the right page. My wife took our 2011 Prius to the Toyota service center this morning. Like others who have posted here, we have had to drive with our high beams because driving with low beams alone in unsafe.
I have an appointment for service tomorrow and, according to most of the posts here, I can expect to have the bulbs replaced. But, isn't there a more permanent fix? According to the research I've done just today, Toyota has been having this problem with the Prius low beams since 2010! I also read that it could be a ballast failure.
Any new information on this problem? I don't look forward to purchasing new bulbs every few month.

 

Your car is now about 6 years old.
What makes you think that the bulbs would have to be changed any more often than every 6 years or so ?

I find it hard to believe that both bulbs would go bad at the same time.
I think it more likely is some other component that has failed, like a ballast, or they really are on "day time running lights" instead of low beams.

 

It would be easier if you could give more information about your car. Does your car have halogen low beams, or HID ones? Halogens do not have a ballast, so you aren't affected by any ballast issue, if you do not have HID.

Some 2010s and 2011s with halogens had a shorter-than-expected-life issue, that there's a known fix for, but that doesn't affect you unless you have halogens. It also seems to be fairly mild: my 2010 is apparently one of the cars with the problem, and I bought the parts to apply the fix, but I've never bothered to do it, as I'm already at 14 months and counting on my first bulbs since I bought the car, and I think I can live with that.

I speculate that people complaining of really short halogen lifetimes have been buying the "extra brightness" halogen bulbs often prominently displayed at the parts stores, and the whole key to those products is they trade off longevity for brightness (and the exponent affecting the longevity is much higher than the one affecting brightness). I'm using bog-standard H11s, which may be why they are not dropping like flies.

-Chap

 

I have a 2011 with the headlight problem. That issue doesn't cause "dimming" it just makes the bulbs burn out quickly. With my issue the headlights burn out every 3 to 4 months, often within a few days of each other. Worse in the winter when I do more night driving, and worse when I tried using the "extra bright" bulbs (as mentioned). Dealership wanted $800 to fix it, even though it's a TSB, because my car is out of warranty (I bought it used with high miles). Fixing it myself would cost about $60 for the new wiring harnesses, but it looks like several hours of work. Honestly, it costs me about $12 a pair for headlights on amazon and takes about 3 minutes to install them, so I've just been dealing with it. I also don't think this is the OP's problem.

 

Thanks to this forum and common sense I solved my issue. After replacing my stock bulbs with LED bulbs and back again, I had my standard bulbs go out one by one. Apparently you can't mix the LED ones with standard ones. No problem. I used all standard ones and the headlights were still real dim. The fix was simple. Since the problem affected both headlights at once, it was a power supply problem. I took out both bulbs. Removed the connector, and made a note of how it went back in. Put the standard bulbs back in, not plugging in the power. It made it easier to make sure the bulbs were inserted and twisted tight. Made sure to straighten out the dangling connector. Then Plug them in one by one and PRESTO. Lights are on and bright.

 

Did you find a solution. We've been having this same problem with 1 of my 2 2012's. Low beams are too dim, brights are fine. Toyota shop said the bulbs were in quite right and needed to be adjusted. They did that and they are no better

 

Look for loose, corroded, dirty ground wire and check the lamp connectors. They loosen up over time, because of the amount of current going across them.
I made the mistake of replacing my headlamp bulb sockets with cheap after market ones, on my truck. Those sockets started melting and the OEM no longer carried them. I finally found some generic ceramic sockets for those bulbs - been 3 years and no more issues. I suggest gently bending the tabs on your headlamp sockets, if they're loose - otherwise you may run into the same problem I had...

Hope this helps.