Which fuse is for HID?

I suggest you look for and test the following, which are all within the main relay/fuse box near the inverter:

1. 40A HEAD MAIN fuse
2. H-LP Relay
3. DIM Relay

There are four other fuses involved:

1. 10A H-LP HI RH
2. 10A H-LP HI LH
3. 15A H-LP LO RH
4. 15A H-LP LO LH

However those probably are OK since you say that both headlights went out at once.

If you do not know how to test the relays, just ask. You'll need an ohmmeter and a source of 12VDC power.

 

A very important clue. HID has only one lamp within the headlight assembly. High and low are produced by a motorized mirror within the headlight assembly.

Since both headlamps remain in high beam, the DIM relay is the most likely culprit. When the car is IG-OFF and the lights are turned off, remove that relay.

This relay has five pins and is single pole, double throw.

Pins 1 and 2 are for the relay coil. Use your ohmmeter to find those pins, there should be some resistance value like 100 ohms or so.

Identify pins 3, 4, and 5. You should find close to zero ohms when measuring between pins 3 and 4, when the relay coil is not energized. You should also find infinite resistance between pins 3 and 5 at that time.

Now, apply 12VDC to pins 1 and 2. You should find close to zero ohms resistance when measuring between pins 3 and 5; and infinite resistance between pins 3 and 4.

If you don't obtain these measurements, then you can feel comfortable that the relay is the problem and buy a replacement from your Toyota dealer (probably cost $50 to $75.)

If the relay is good, then you would have to suspect the body ECU or the headlamp switch mounted on the steering column. Both are much more difficult to get to, so I hope the relay will be your problem. Good luck.

 

Patrick,

I read your posts, as I have had the same issue noted above by imagesetc. I purchased a new DIM relay and installed it and it did not correct the problem. Would the HL relay need to be tried as well? Are there any other steps to take to get the headlights working again?

Thanks

 

"same issue" means that your headlights work in the high beam position only. Please confirm whether this is the case.

 

Apologies, yes, the "same issue" means that my headlights work in the high beam position only.

 

If you swap the HL relay with the DIM relay if the lights do not come on at all the DIM relay is faulty. Mark the relays H & D before swapping to avoid confusion.

 

The DIM relay is single pole, double throw while the H-LP relay is single pole, single throw (at least this is true for North America models.) Hence it will not be helpful to swap them.

I suggest that if the DIM relay has already been replaced, then check the 10A H-LP HI RH and 10A H-LP HI LH fuses. If those are good then it is possible that the dimmer switch on the steering column is bad.

 

Yes I agree but looking at the wiring diagram what I said still stands as the relays are mounted with the same base configuration. The DIM relay does not even need to be fitted to make the HI work and if changed to the HI position will make the HI lamps work if the relay is ok. Just simpler than checking with an ohm meter and geting a 12v supply to the relay.

 

I cannot swap the relays on my 2007 Prius. Well, I should say that I cannot insert the 5-PIN DIM Relay into the 4-PIN HL Relay slot. I can, however, insert the 4-PIN HL Relay into the 5-PIN DIM Relay slot. I am skeptical to mess with the 4-PIN HL Relay though, since I can only drive at night with my high beams currently and if something additional goes wrong, I wouldn't want to be in the situation of having no headlights at all. I guess I will order the 4-PIN HL Relay to replace the current and confirm that there is or isn't a problem with that Relay.

 

The H-LP relay is not the problem and you will be wasting your time and money to replace that. Proof of that is you say the headlights work under high beam. If the H-LP relay had failed, there would be no power to the headlights at all.

I suggest you check the two fuses cited in my post #9 and if they are good, then seek professional assistance as it is likely that the headlight dimmer switch has failed. This is not easy to get to since the steering wheel hub has to be disassembled which involves handling the driver's side SRS airbag.