How to Replace the HID Ballast/Computer/ECU
2004-2009 Toyota Prius


Before doing anything read my disclaimer & safety info.



A common problem with Prii that have HID headlights is that they'll turn on and then randomly go out. This could happen to one or both headlights. It/they may cut out altogether or slowly fade out. As you can imagine this is a serious safety issue and there's a class action lawsuit regarding this. If you meet the guidelines there you can probably get this taken care of for free. The first thing the dealer will probably do is replace the bulbs. This may fix some but not all. I tried that and didn't get 5,000 miles before the exact fade out issue started happening again on the exact same headlight. So, I replaced the ballast and have not had a single problem over 14,000 miles in 15 months (update 1/24/2015: still no problems since the replacement ~ 3.5 years and 35,000+ miles later).

Update 1/24/2015: I had a ballast fail in my 2009 Prius due to water condensation inside the headlight assembly. Somehow water got into the headlight assembly which then finds its way to the bottom where the ballast lives and it eventually explodes. It doesn't matter there's a decent gasket on the ballast, it's coming top down from the inside and the inside of the ballast is not protected. So some portion of the headlight assembly failed and let water in. I added hot glue around my entire lens/assembly so hopefully this won't happen again.

Although I'm just now putting this tutorial together I did this fix on 5/30/2011. This will be a mix of photos from then and some more recent ones I took. In doing research for this tutorial I found a pretty good video on it which I'll have at the end. In this video I realized what I could have done to make this job much easier. As you'll see, the headlight bulb connector doesn't fit through the headlight assembly to remove the ballast. The key is to remove the connector. Lastly, Toyota calls this part the "headlight light control ECU sub-assembly" in the repair manual. All aftermarket parts/kits refer to this simply as a ballast.

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Tools Needed:

Parts/Supplies Needed:

1) Pop the hood and remove the headlight assembly.

2) Rotate the headlight socket cover counter-clockwise to remove it. You can see the "OPEN" along with the arrow.

3) Rotate the headlight bulb connector counter-clockwise to remove it.

Optional: Replace the HID bulb. Just push in and guide these 2 wire holders outwards and it will release the bulb. For those who don't want to do bulb replacement by feel as in the linked tutorial this is super easy.

4) Remove these 4 phillips screws.

5) Push in on this tab and remove the cover wiring connector. As you can see from where the silver braided cover comes out, there isn't much room there.

6) To get the ballast out you need to remove this big black plastic connector....

This pic is just for reference. Part #85967-24010 is original and in there. Note that it says D4R, D4S 2000H, so a multi-car part used in many Toyota & Lexus models. My personal opinion is that the 2000H means, 2000 hour life but hey, I could be totally wrong (if someone knows email me). It just seems as though these things start to die after miles and that would make sense with high hours. Also note that my connector is cut, that's because I didn't know of the following trick yet. You will most likely be doing step 6 with the ballast wiring still running through the headlight assembly as the previous picture shows.

6a) Use a thin flat-head screwdriver or needle nose pliers to bend these two metal tabs up as shown.

6b) There are a couple of small plastic tabs you where you'll need to bend the metal casing outwards so it can be removed. With the metal cover off, pull the metal braided sleeve back so you can see the plastic. Pic #6 shows the metal casing removed with the braided sleeve still on.

6c) Use a thin flat-head screwdriver to bend these two plastic tabs up while pulling up to separate the two pieces of this connector. We're just taking it apart so we can remove the wires.

Here I've separated one side, repeat on the other side.

6d) Now flip it over and use your thin flat-head screwdriver to separate the two plastic hooks by the wires and it will come apart in two pieces as shown.

6e) Now that the connector has been separated the two wires easily pull up and out. WARNING: I have no idea what may happen if the two wires touch or how long these ballasts retain voltage. To not take any chances remove one wire at a time and cover the exposed metal connector with electrical tape. There is a high voltage warning sticker on this thing after all.

6f) With the bulky connector removed you can now easily slide the wires out of the headlight assembly.

7) This step varies depending on the replacement ballast you get. Pictured on the right is the original ballast (don't pull the braided sleeve back like I did, it makes it extremely difficult to put back on), part #85967-24010. On the left is what I bought off ebay (for my first Prius ballast replacement), part #85967-52020. The seller claimed it would work but as you can clearly see, the wire lead is short by 3-5 inches or so and that matters. Not having anything else I just cut and spliced a longer section in so it matched the original part length. I then took the original metal braided cover (some type of ground maybe?) and installed it on the new ballast to correspond to the longer wires. So this step has two methods...most of you will likely use method 1 since it's much easier and cleaner.


Method 1
Replace the ballast with the original ballast part #85967-24010 or this OEM replacement.

7a) Repeat steps 6a-6e to remove the bulb connector on the new ballast.

7b) Feed the ballast wiring through the headlight assembly taking the shortest path to the bulb and then reassemble the bulb connector reverse of removal 6e-6a.

Method 2
Use a different part # like I did such as part #85967-52020 (there are others too) and harvest the braided shield from the original ballast and then cut the wires and splice in longer ones so it will fit the original length, install harvested braided shield.

7c) Remove the 3 phillips screws circled in red.

7d) Remove the cream colored plastic cover that shields the circuit board.

7e) Pull up by the blue arrow to separate the braided shield's clamp.

7f) Use a thin flat-head screwdriver to release this clamp. Before you pull this shield off slide something in thin like a piece of metal wire (coat hanger, single piece of electrical wire). Once this thing gets bent out of shape it's almost impossible to get it back to form - learn from my mistake.

Remember that high voltage warning sticker on the casing? Maybe that's why all these circuits are covered in this strange goo?

7g) Repeat steps 7c-7f on the replacement ballast so the original braided shield is off.

7h) Here's where my pics just won't match up exactly, this one is the closest I have. Now that the 2 braided shields have been removed you should just have the 2 ballasts with wires coming out of them (uncut), 1 original and 1 replacement. In this step you want to cut the wires of each to match the OEM length. You can lay them out like this to make it easier. As you can see I staggered my cuts a bit and moved the longer wires to the new ballast. You can either use butt-connectors and electrical tape or solder the connections and use heatshrink tubing or electrical tape to cover it. Now you just install the braided metal shielding and assemble the ballast reverse of removal. Remember not to install the bulb connection until you've fed the wiring through the headlight assembly!

8) Now you can reassemble the headlight bulb connector and put everything back together reverse of removal. Before putting the headlight assembly back in completely I'd recommend hooking up the wiring harnesses and testing to make sure the headlight turns on. If so you can put it completely back together and congratulate yourself on the hundreds of dollars you just saved!

Here's the second ballast I replaced, this one clearly died due to water.

Many components fried!





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Last revised: Sunday, 29-Oct-2023 16:36:56 EDT