Where is the headlight relay on a 2006 Honda Civic DX?
 

Hi, both my headlights stopped working at the same time. I've check the fuses for the headlights, (21, 13 and 12) and they are not blown.

I get voltage to one side of fuse 21 (21 to ground), but I do not get voltage at 13 or 12 when I flip the headlight switch. My guess is that either the switch or relay are not working.

I cannot find in the manufacturers manual where the headlight relay is located. Does someone know where I can find this relay?

Thanks

Have you checked the bulbs? You're discounting that it might be bulbs because you think they both went out at the same time-- but reallly whenever something on a car doesn't light up, always check the bulb first and go from there.

The diagram suggests the relay is attached to the interior fuse box. With the light switch on (low) you should have power on both test points of fuses 16 and 17. Measure voltage from the test point to ground.

Thanks for the response. I checked fuse 17 and 16 to ground with the low beam headlight switch on and did not read any voltage. In the first post I incorrectly wrote fuse 12 and 13 instead of 17 and 16.

For comparison the high beams work and I get 12V when I turn the high beams on and check fuse 12 and 13 to ground.

I have not tried changing the light bulbs. I bought a spare set but don't want to open the package and install until I'm sure I get voltage across fuse 17 and 16.

A co-worker of mine thinks that under-dash fuse/relay box contains a part called the MICU. The MICU likely contains the low beam headlight relay. I'm investigating this.

Is there voltage on both ends of fuse 21? This feeds the relay for low beams. You can check the combination switch by looking for a voltage change on the pink wire. But if you can leave it pushed forward to the high position and turn the high beams on and off by twisting the switch, it seems the switch must be working.

On 2001 - 2005 models the MCU was replaced by changing the whole fuse box. It was not sold separately.

There is voltage on only one side of fuse 21.

I confirmed that the headlight switch turns off the high beams. I'm wondering if I can switch the connections out of the fuse box so when I turn my high beams on I get low beam lights. I live in the city and rarely use my high beams. This would at least let me temporarily drive at night until I can get the fuse box switched by the dealer.

If I switch the white and green wires and then the purple and pink this might work?

Voltage on only one side of a fuse means that the fuse is blown, or defective. Replace it.

mk378, you're first response was correct. It was the bulbs. To try and save a buck and because I believed that both bulbs went at the same time I did not replace them but jumped straight to the fuses and switches. This was a big waste of my time.

However, I still don't understand why:

1. With burnt out bulbs, I remove fuse 17 and 16 with needle nose pliers and check the voltage to ground (to the chassie) on both sides of fuse junction 16 and 17. I get no voltage to ground on any sides of the fuse junctions. I checked this multiple times and I'm sure of it. To confirm that I was using the voltmeter correctly I removed fuses 12 and 13 with pliers and checked fuse junctions 13 and 12 to ground and got 12V.

2. With functioning bulbs, I remove fuse 17 and 16 with needle nose pliers and check the voltage to ground (to the chassie). I get 12 V from one side of the fuse junction in both 16 and 17.

Based on the wiring diagram I don't see how this is possible. Any thoughts?

Thanks again for your help. You had the right advice from the get go.

That doesn't make a lot of sense. Are you sure you're measuring properly? Set meter on DC volts and put the black probe on ground. Finding a good ground is not as simple as it sounds. Inside the car the metal shell of the lighter socket is a good place. Under the hood use the battery minus terminal.

It is not necessary to pull fuses out for testing. Since it's a low voltage system without a significant shock hazard, car fuses are designed with two exposed metal nubs on the top of the plastic (where the amp rating is marked) which are live-- they're connected directly to the two pins on the bottom. Touch those test points with the probe of the meter. It is better to learn as much as you can by passively probing than by actively disturbing the circuit.