2014 RDX with 457k miles. My driver side low beam is not working. I moved the working bulb from passenger side. Doesn't work. Then checked the connector. it shows 0 volts. Checked connector on the passenger side. Shows 14.5v. Checked Fuse 23. It is good and shows 12.5v. So i am guessing a relay is broken. But relay is supposed to control both bulbs. I can't find where this relay is in the fuse box in engine compartment. I looked at the underside of the fuse box lid. Can't figure out which one if any is a relay possibly causing this issue. Does anyone know? Should I look elsewhere? Thanks.

 

Oops—did your driver's-side fuse box happen to get flooded?
Did you check what is missing—12 volts or ground?

You have LED bulbs in your headlights?

 

Wow! Is this the highest mileage RDX on these forums? That's a round trip to the moon!!

 

There was no flooding. About a year ago I did have to change the fender liner which was torn. So there may have been some water spray on to the engine bay from rain water. This time I saw that the headlight bulb cap came lose and was hanging when I looked to check the bulb. The engine bay sure is dirty. I don't know how to check 12v or ground. Not that handy. Bulbs are halogen.


Thanks.

 

I should clarify about the connector I tested. I removed the headlight bulb cap since it was filthy and cleaned it. Before I put it back on, I tested the connector which inserts into this bulb cap in the attached photo. It showed 0 volts. So there is no power to the bulb.

 

The driver-side fuse box is not the engine bay fuse box. However, if you do not know how to check for 12 volts and ground, or if you are unable to read wiring diagrams, you should consult an auto electrician before you burn something out.

 

Good point. No flooding. Can you please share diagram 2 of 2 for the headlight wiring? Thanks.

 

Oops, I just noticed that the diagram actually shows the high beams—LOL. But the fuse box under the hood looks so dirty, it’s as if it’s been sitting there without a cover.
It's a good thing the low beams use a relay rather than a MOSFET.
Swap the relays—the right one for the left—and see what happens.

 

Removed the bulb cap and put it aside. Checked the connector that goes into the bulb cap. The black ground wire connection shows 12.6V. The purple wire into the connector shows 0.00v. Ran the multimeter red probe up and down the wiring from connector. No spike in volts. I don't know where the connection is failing from fuse to the connector. I pulled gently on the purple wire. it didn't come out of the connector.

 

Got new relay. #15 is for the passenger side low beam. Figured that out by removing #15. The passenger low beam went away. Put it back and light came back on.
Next, swapped the relay from #14 to #15. The passenger side lowbeam still works. Driver side is still dead. So it looks like the relays are not the problem. I didn't see any corrosion in the sockets.
I did not check any other relays.

 

The next step is to check the voltage at the relay pins to see what is missing.

 

So I need to pull the relay out, check voltage on pins in the empty socket?

 

Yes, you need to connect everything, turn on the headlights, remove the relay, and then there should be 12 volts—supplied by fuse #23—at pins 1 and 3. Pins 2 and 4 should have ground.
And then you'll find out which side your problem is on.

 

I am not sure about the pin numbers. I tested all 4. The pin on the top right as I am looking into the socket shows 0v. The one below it shows 12.4v.
The pin on the very left shows 12.4v. And the pin the middle shows 0v.
These are the same readings with lights on and lights off.
And the same readings with socket 14 & 15.
i attached the bulb, it works!
I have no idea why and how. If you know what might have caused this issue and why it is fixed, please let me know.
I hope it is not temporary.
Thanks for all your help. Appreciate it.

 

Light is dead again. So much for that.

 

It sounds like there's a bad connection somewhere.

 

I'm thinking the same thing.

 

Worked on it just now. Replaced the relay with new one. I was thinking the wire from relay to bulb cap is the problem. When the problem started, I looked at the bulb, the cap was hanging. I can never get it to fully go in. So used gorilla tape today.
Scratched around the pins in the socket for good measure if there was any unseen rust.
The light came back on.
I was thinking of harness relay if this continues.

 

One of these terminals should have 12 volts, while the other should be ground. Additionally, when troubleshooting, you can bridge the terminals with a jumper to rule out any issues on the control side.

 

The one on the far left has 12.5v. the one in the middle always 0v. the two on the right also have 12.5v.

 

If you apply 12 volts to the middle terminal and the bulbs still don't light up, then the problem definitely lies somewhere downstream of the relay.

 

Replaced the headlight bulb cap with a new one. The light is now on. Hopefully this is resolved.