How to improve Gen 2 Prius Headlights? Extremely Weak for me.

Might be the hid ballasts going bad. Also, are your headlamp lenses foggy?

 

The ballasts are a common problem on the 2nd gen from what I've read. When they are going bad, you usually have to turn the headlight switch off and on for the headlights to turn on. My passenger side is does this once in a while and the bulb has already been replaced so probably the ballast.

edit: There are people that say they are dim for being hid's so maybe this is the case.

 

If the light is outputting, then the ballast is working. The ballast "problems" you describe is really not a problem, just Toyota putting the wrong language in the service guide and causing lots of problems that way. If the ballast wasn't working, there would be no light.

If the light comes on after turning the lights on and off a couple times as TheMoles describes, that is a bulb issue, not a ballast issue. That means your bulbs are dead and need to be replaced. Yes dead even with light being emitted.

The OP's problem is different.

When a HID bulb is new is does produce more light that slowly decays over time. It also colour shifts 600K to 1000K unless you bought special non-colour-shifting bulbs. (usually have the "+" marking after the product code).

With the Prius, they are reflective HID bulbs which is different than almost all other HID cars. Most cars have projectors, you have reflectors. It will never be great. But it is also effected more by alignment. That's my guess at your problem since you've had the problem since you bought the car. And dealerships are crap at aligning bulbs.

Find a nice flat are with a large wall infront of it. I like the loading dock area of big-box stores in the US, or the back of a large shopping mall. Usually they are flat and have large wide and tall sections with just blank wall space. Pull up bumper to wall. Put a little bit of tape horizontally on the wall at the height of the bottom of your headlights and make a vertical line at the center of the headlights. That should mark the center of the headlight beam horizontally and the bottom of the light beam vertically as it escapes your headlight at bumper depth. Now back up 25ft straight back. The headlights will now be spread out. Put another piece of tape or something you can mark to use as alignment from 25ft away 1inch below the horizontal tape. Now at your car aim the headlights so that the headlights still hit the vertical center but now the bottom of the beam hits the mark you made 1 inch below the original mark.

Now your headlights are properly aimed and you should get better results on the road.

 

Might be defective autoadjusters. There's a sensor connected to the rear axle that can go bad.

 

I don't think it's connected to the CAN bus. So no code - it just leaves the aim of the headlights wherever the sensor came to rest.

 

The only bulbs that seem to work are genuine Philips brand D4R. Costs at least $50 per bulb. Cheaper bulbs lose brightness quickly like you've experienced. If anybody else has good experience with non-Philips, please speak up because there's a lot of garbage out there.

 

Those "8000K" bulbs will be trash and will not be brighter. They are also illegal in many places.

The bluer the light, the more your eye picks it up because humans are sensitive to blue light. It is not brighter, but it will look brighter on a clear night. 8000K is either way too far on the spectrum or a bold faced lie.

Stick with the Phillips bulbs.

If you want another solution, I characterized a projector set off of eBay a few years ago made for the GenII Prius, and surprisingly it wasn't bad. I currently have them installed on one of our Prii. They were made for halogens H11 bulb base and as such the squirrel finder is way too large for HID luminous output. But they are easy to access and a little bit of metal tape (ducting tape, NOT duct tape the gray stuff) will make them great. The cutoff is decent, the spread is OK with only a bit of a hotspot and are adjustable.

So for about $200 you can get projector headlights. An hour later they will be installed in your car. Buy either an H11 to D4R base adapter or buy D2S bulbs with an H11 base and then modify the ballast connectors.

You can't match the light output even with brand new reflector based HIDs. Note that my Prii were all halogen stock. One has Lexus RX450h projectors retrofitted inside halogen housings ($$$) and the other has these eBay projectors ($).

 

Maybe your car has a wiring problem such as a loose ground connection?

 

In principle the way to troubleshoot would be to measure battery voltage at the power input to the HID ballast. It should be close to 14V when the Prius is READY. You could also measure resistance of the lead connected to the body ground. The resistance should be very close to zero ohms, like no more than 0.2 ohm.

Now, the reality is that it may not be easy for you to identify the correct wires and successfully measure as per the above.

 

Time to start checking voltages. If the lights even turn on, then the ballast is functional enough to start the HIDs up. I don't know what the startup and operating voltages are, so you'll have to check those specs. I'd look at the voltage at the bulb connector. Headlight aim is also important - there is a sensor at the rear axle that controls vertical aim. My 2006 headlight lenses are getting fairly oxidized, so maybe a lens cleaner would help.