2005 TB Lowbeams gone, not fuses or relay

[Charles Austin Miller]

Both lowbeams went out on my 2005 TB LS EXT a couple of nights ago. Halogen bulbs are okay. Left and Right Low HDLP fuses (#3 and #5, I think) are okay. Headlamp Relay fuse (#53) is okay. Headlamp Relay (#46) tests okay, but I replaced it anyway.

Still no lowbeams. What's next?

 

[Matt]

Did you check the sockets for signs of arching or melting? It happens.

 

[Blckshdw]

If the fuses tested as OK, can you confirm you're getting power to the sockets? How about the relay socket, power getting there too?

 

[Charles Austin Miller]

No signs of arcing, all fuse and relay posts are clean, like new, although I haven't tested individual sockets. Then, again, if a socket is dead, what is behind THAT?

PCM or BCM failure?

 

[budwich]

get your meter out and check for voltages along the "path" of components and also check the operating electrically conditions at the relays .... as in "are they operating" when they are supposed to?

 

[Drec]

You might take a look at the dimmer switch. It could be almost anything, but will take some troubleshooting with a meter and wiring schematic.

 

[mrrsm]

 

[budwich]

??? not sure how the dimmer impact the headlights... maybe I am missing something.

 

[Drec]

??? not sure how the dimmer impact the headlights... maybe I am missing something.

On simpler automotive designs that I'm used to, the high and low beams are controlled by the dimmer switch. A hot wire from the light switch goes to the dimmer switch, allowing you to select either high or low beams.
That said, looking at my 2002 Service manual, I would suggest looking at the applicable Service Manual for the vehicle in question. My 2002 Service Manual has a section on "Lighting Systems", "Headlights Inoperative-Low Beams"; which has a step by step diagnostic.

The more I look at the Service Manual, for these vehicles, I'm glad I bought a Tech2 Clone.