For the past year and a half I've had trouble with the headlights on my 2004 Prius. It started when just the left headlight started randomly going out. I replaced the bulb, but that didn't solve the problem. A few months ago BOTH lights started randomly going out. When this happens, 99% of the time simply turning the lights on and off again will fix it. The other 1% of the time you have to flip them on and off multiple times before they'll come back on. It tends to happen in spurts. It'll go months without happening at all, and then all of a sudden it'll keep happening for awhile. The dealer told me I need to replace both bulbs, but this sounds suspicious to me because (a) the one bulb was replaced, and (b) they keep turning back on, which seems uncharacteristic of a bulb burning out. I've seen where there's a recall on other year's for what sounds like the same problem, but 2004 is not part of it. Has anyone else experienced this and found a solution? The dealer just wants to replace the bulbs, and if that really solves the problem I'll do it, but my husband and I are on an extremely tight budget and I don't want to waste money on things that aren't actually the problem.
Try replacing the bulb that wasn't replaced first. Bulbs are meant to be replaced in pairs. Also don't buy the same Brand bulb as you bought last time, try a different brand.
I don't know how common that is with other cars, but you read about it all the time on the threads here. Those bulbs seem to be very sensitive, you might even have a bad bulb on your replacement. I would try to replace both this time and see what happens.
Does your car have halogen or HID headlights? (A clue: if your car is equipped with factory fog lights then it has HID headlights.) If your car has HID headlights, where did you source a replacement bulb?
If you do not have HID your issue is most likely the same issue I had and that was burnt connectors. The plastic connector itself that plugs into the bulb. Take a close look at the metal connector itself inside the plastic housing and you may see some burnt areas. The final tip off is if the plastic housing looks deformed from heat. I replaced the connectors on mine and no issue since. I was quite a pain though. Mine was because I drive with the headlights on all the time.
I also drive with the headlights on at all times and am having the same problem with one headlight intermittently going on and off. If it is the connector, how did you replace it? Did you solder a new one in?
I have the EXACT same problem the OP has. Everything she wrote is exactly the same issue I have! It is always the left bulb which occasionally goes out. I flip the switch and it reignites. The left bulb burned out about a year ago and I replaced it. The right bulb was replaced around 3 years ago. Someone mentioned that it may be an issue with the computer that is responsible for the HIDs. Ironically, I too can go for months with no issues, then all of a sudden it will repeat happening for a few days. I won't even bring it to the dealer because I'm sure they won't be able to diagnose it. Something intermittent like this is very annoying. Since my car is 11 years old already and has 238,000 miles I tolerate it. The car has been extremely reliable and all I've ever done is normal maintenance and the associated recalls/TSBs etc.
