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Prius headlights - worth the cost to fix?

Our 2005 Prius has about 163,000 miles and we have had it serviced regularly. Recently, the left headlight, both low and high beams, failed. Later in the day, both high and low worked. The next day the right headlight did the same thing. Now the right mostly fails and the left is fine. If we turn the switch on the steering column on and off a few times, sometimes they will both work. The dealership did a diagnostic check and said that the computer (microprocessor) on each headlight probably needs to be replaced. The cost is $750 to do both plus $250 for labor. Why would both microprocessors go out in the same weekend and sometimes work if the switch is turned on and off? Does this make sense to you? We figure the Blue Book value of the car is about $2000 or so and are debating whether to buy a new vehicle. We were hoping to get to 200,000 miles. The car works well otherwise except we have to add oil more frequently than in the past. We bought the car in Philly but moved to Helena Montana shortly after. It gets dark early here now!!! Thanks!

Why, they don’t give awards for that. I myself would not put 1000.00 in this thing. You are in Montana and I would be looking at a new something that is more suitable for the extreme cold and snow now before stranded becomes a possibility.

how long will it take to drive 37k miles? 1yr? 2yrs?

What kind of headlights require their own computer and cost a thousand dollars to repair? wow!

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I’d try and find a shop that specializes in auto electrics. It could be just the switch, or it could be a loose/corroded connector, but some time with a voltmeter would clear this up.

What kind of headlights are these? LED? HID?


Yes, the dealer’s diagnosis should be questioned. A close study of the wiring diagram will probably lead to a single common factor that is working intermittently. Has the dealer looked up TSBs or other info from Toyota that could apply?

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I’d also go to a Pruis forum like Pruischat and look for posts related to this problem. It’s unusual enough that others may have had the same thing happen.


The dealer’s statement that the microprocessors “PROBABLY” need to be replaced is a big red flag for me. A second diagnosis is definitely in order.


Your car needs new HID bulbs. When the HID bulb reaches the end of its service life the operation becomes intermittent, they stop working when they get hot.

When a headlight ECU fails they don’t start working again.


I agree with @Nevada_545 above. Sounds like your HID bulbs are failing. They both have yhe same hours of use, so concurrent failure isn’t that rare. I would have an independent shop replace the bulbs for a couple hundred bucks and drive on.


Yeah probably bulbs but when my HID light went out, they said it also could be the exciter or whatever it’s called and that was about $700 (under warranty though). At any rate gee, you want to go another 37,000 in a Prius in Montana with winter coming? I think I’d just call it a day and trade early and be done with it. What are ya gonna save going another 37K?


For myself 37,000 miles would mean 5 more years of use, how much did your $50,000 vehicle depreciate in the last 5 years?

Sell/Trade a car because the headlights are broken? what is this world coming to?

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I find it hard to believe that there are “computers” controlling each headlight, and if there really are, I find it even harder to believe that they both could have failed simultaneously. It sounds like even this dealer isn’t too confident in the “diagnosis”, as they said “probably”, not “confirmed via test equipment”.

I suspect the problem is either with the headlight switch, the bulbs themselves, or a loose connection/damaged wiring harness. It should be possible to replace the bulbs for a lot less than $1000, especially if you DIY.

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my coworker used to own Prius of similar vintage and mileage, he’s also developed an “intermittent left headlight drop-off” symptom, similar to the OP description

he usually maintained his old Prius at a nearby Toyota dealer, but to their credit, they were always more or less reasonable in their fixes and maintenance

his repair was around $200 and the root cause was identified as a faulty ground wire or headlight wire, I do not remember, but they definitely fixed him us for much less than $1000

The HID ballast on a Toyota is called a “Headlamp light control computer sub-assembly” or sometimes headlamp ECU. There is also a headlamp leveling ECU.

In most cases the HID bulb has failed, I replace about 25 HID bulbs for each ballast ECU. Perhaps in small town Montana they have little experience with HID headlight repairs.

I also find it somewhat amusing to get rid of a car due to headlights. This might be a first.

I am sure the prius chat website mentioned above has a DIY on how to change the HID bulb and Ballast. Might even have a DIY on LED conversion. I just put LED’s instead of my regular halogen fog lights. It was an easy swap and they are superb.

Find an independent shop or even a car stereo shop and see how much they will charge you.

You have to remember that the voltage for an HID bulb is about 20,000 or some where around there. Even with the factory manual, I left that job to the dealer. These are not like dealing with a normal halogen bulb.

how do you drive a car with nonworking lights?

That’s the strike voltage. That’s only present for a brief period when they start. After starting, the voltage drops to around 90 volts. Regardless, there is no need to fear these lamps/ballasts. Just like a halogen lamp, you shouldn’t be replacing them while they are illuminated…