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Horn works intermittently

My horn works in park but not drive… specifically when auto door lock engages at 15mph the horn stops working. Any ideas on a fix?



It’s a 2011 tundra

There’s a customer interest bulletin on the horn, involves the radiator/horn mounts cracking. SB 32-12, 2.2.2012. Good idea to check if that has been done.

It appears to be a pretty simple design, the switch you press grounds the coil of the horn relay via some sort of spiral cable assembly, that coil energizes and closes a contact which powers the horn with 12 volts from the battery. There’s actually two horns, one for low pitch, and one for the high pitch. If you can locate the contact which ground the relay coil, your shop could probe that as you pressed on the horn to see if it was getting grounded or not. Pin 7 of the unit E integration relay from what I can see. If that wasn’t being grounded solidly, for example the horn switch was corroded, such a symptom could result if some other circuit was turning on & slightly lowering the voltage to the coil circuit.

There’s also an alarm horn relay, but seems unrelated to your symptom. If you can disable the car alarm, worth trying to see if it makes a difference I guess.