Horn Don't Work

[JohnnyR]

05 GMC 2500HD Duramax. Horn quit working, both of them. Checked fuse and relay under hood. Both good. Pulled horns and they work on direct power. What am I missing? I assume theres a contact switch in the steering wheel. I've never had one fail before. Am I missing something?

[jbplock]

Johnny,

FYI .. here’s a snip from the service manual

“Horn CIRCUIT OPERATION: Battery positive voltage is applied at all times to the horn relay coil and the horn relay switch. Pressing the horn switch applies ground to the horn relay control circuit. The body control module BCM may also apply ground to the horn relay control circuit as described above. When the horn relay control circuit is grounded, the horn relay is energized and battery positive voltage is applied to the horn(s) through the horn control circuit. The horn(s) sound as long as ground is applied to the horn relay control circuit.”

I would check the horn input to the BCM (to find the pin# you’ll need the HELMs manual or access to alldatadiy.com). The BCM is under the dash on the drivers’ side. If the input doesn’t go to ground when you press the horn button it would point to the switch or a wiring problem. Also manually ground the BCM horn input to check that the BCM horn circuit is working. If wiring it could be the SIR coil (clock spring) on the steering wheel. The SIR coil consists of a coiled up flex circuit that routes wiring from the moving steering wheel to the harness on the column. ..had to replace mine .. I stated getting a “service air bag” message in the DIC and the radio buttons stopped working. To replace the SIR coil you have to buy the complete steering wheel harness .. not cheap – about $200 (300 list) – if you don’t have the steering wheel controls it may be cheaper. To replace remove knee bolsters, dash covers, airbag, and steering wheel.. GM steering wheel puller is also needed.

[JohnnyR]

Did a search on this site and found a post from DmaxMaverick in 2001 that told me how to pull the horn switch from the steering wheel to clean it, and that fixed it. Only difference was the airbag fuse is under the hood vs in the cab on a 2001.

[Mark Rinker]

My C4500 horn works, but illuminates the airbag warning lamp until the key is cycled, if pressed repeatedly...(DON'T ASK HOW I KNOW THIS)...I keep waiting for the bag to blow up in my face some Monday morning in traffic, as I'm honking at somebody to get the &^%$ out of my way...

[Heartbeat Hauler]

My horn just stopped working also and I was just about to post the question "Now what?" Now, I know what to do. Life is all about timing...
Thanks guys,
JP