I currently have a 2010 Prius 4 with the , the stock, what I think is halogen headlights. About two days ago both headlights went out and it does not appear to be that the bulb is bad or that the fuse is blown, I am getting about 14.1v volts to each connection. I am kind of a loss and don’t want to go pay someone a few hundred dollars just to tell me they need to pop in a relay or replace a switch. Any help would be greatly appreciated. Other info: High beams work, running lights work, when I hit the switch for the lights the dash lights dim and the navigation inverts its color it always does when the headlights are working.
If you are measuring at the right spot and getting 14.1 v with the light switch turned on, and 0 V when turned off that would suggest the switch and fuse are okay. It would also implicate the bulbs. Granted, strange that both would go out at the same time. If you take the bulb out and measure the continuity across the bulb terminals, you will get zero ohms if it is good, and infinite (no connection) if it is bad. (as always do not handle a halogen bulb by the glass or when inserted and lit, it might pop.)
You said you were getting voltage to the connections, did you mean the connector at the back of each headlight assembly? If so, as Big Steve said, you have eliminated everything except the bulbs and the ground connection. But it is unusual for both bulbs to go out at the same time. The only fuse I can find on the wiring diagram for the low beams is #19 in the under hood fuse box but if you have voltage to the headlight assemblies on low beam that fuse would have to be good. Check the ground connections and make sure they are OK, I don't know if both sides use a common connection or not. I guess if it were me I would buy a couple of new bulbs, if it turns out to be something else you will have spares.
I was measuring from the terminals that connect the bulb to the harness, when you said ground connection what exactly do you mean? I am with you the only fuse I can find is #19, I found a few places on line that mentions the relay going bad but I can’t really find where said relay is as I would just rather try a known good one to rule that out. I will go out at lunch and see if I am getting any continuity across the bulb, though visually they looked fine when I pulled one out. Where would you recommend finding the part number for the new bulb, or where would you recommend my buying them from?
The bulbs are usually marked on the base as to what model they are. You can usually pick them up at the local auto parts store.
Most auto parts stores have an application guide that will recommend the correct replacement bulb for your vehicle. If you don't want to troubleshoot- just get a spare bulb and replace one of your old ones- if it illuminates- it's probably a bad bulb. If the new bulb doesn't illuminate- then you have a ready spare in your roadside breakdown kit. Remember to wear clean gloves and don't ever touch the glass on halogen bulbs.
Don't forget, the manual also tells you which bulb type it is as well if you're ever in doubt. If the auto parts store isn't convenient, Walmart also carries bulbs, as does K-Mart, Target, and probably some other retail stores that I'm not familiar with.
My first bulb just burned out at 80,000 miles. I went to a local auto parts store and paid $12 for a new bulb. It took 60 seconds to replace. I would give a new bulb a chance to see what happens. I have a backup in the trunk. The other one will go soon.
While it's unusual for two bulbs to fail at the same time, it's not unusual to not notice the first failed bulb. When the second one fails you think both went out at the same time. Tom
To check the ground use an ohm meter on a low setting (or auto range) and check continuity between the ground connection on the plug that goes to the headlight assembly and a good ground such as the engine block. Should be close to zero or maybe a tenth of an ohm or so. If the bulbs fix it don't worry about checking the ground though.
I always park directly behind my pickup, which has a chrome bumper, so I can easily verify my headlights and parking lights are working every time I start up the car in the morning by looking at the reflection in the chrome. I favor the idea that both bulbs didn't go out at once, but once the second one went out it became obvious that both were dead.
But only do this test with headlights turned off, otherwise you can damage the ohmmeter. You can also do this test with a voltmeter set to read 12V. Attach one lead of the voltmeter to a good ground, like the engine block, and then measure the voltage on the ground connector of the headlight assembly with the headlights turned on. If everything else is good but the ground is bad you will read around 12V on the ground connector. If you read zero something else is wrong. Tom
Though none of them looked blown, i replaced the fuse and both the lamps to resolve the issue. I guess it just seemed so odd that both would go out at the same time that i just assumed that it had to be some thing bigger then just a fuse or lamp issue.
