Toyota Sienna horn not working — Diagnose and fix
To fix a Toyota Sienna horn not working you work the problem just like any other horn issue, staring with the fuse and horn relay and the power feed to the horn switch in the steering wheel. Then things get a bit tricky.
Most horn circuits supply power to the horn switch and when you press the switch, you complete the circuit to ground with activates the horn relay. The problem with the 2000-range Toyota Siennas, is that they didn’t use a traditional horn switch ground wire connection. The horn is grounded through ball bearings in the combination switch which is mounted on the steering shaft. Over time, the grease in the combination switch bearings can dry out and the ball bearings can corrode. That’s when you lose the horn ground connection to the steering shaft. I’ll show you in the diagram below.
Toyota Sienna horn wiring diagram
Power flows from the horn fuse to the input side of the horn relay control coil and the horn relay contacts. From there, power flows to the horn switch. In a properly operating system, pressing the horn switch completes the circuit to ground through the ball bearings and then to the steering shaft to ground. That energizes the horn relay control coil which moves the contacts to supply power to the horns. The horns are ground at the center portion of the engine compartment.
Toyota Sienna horn diagnostic procedure
Power comes to the horn switch on a green/black wire. It should have battery voltage at all times. Backprobe the horn switch wire with your multimeter set to DC volts to check for battery voltage. With the meter still connected, press the horn switch. In a properly operating system, the voltage should drop to around .3 volts. If yours stays above that, you have a grounding problem with the ball bearings in the combination switch. You now have three options; replace the switch, clean and regrease the bearings, or install a hard wired ground connection for the horn switch. All three options involve removing the airbag steering wheel, clockspring and combination switch.
Follow a shop manual for proper airbag depowering procedure and steering wheel disassembly.
The Toyota combination switch is Turn Signal Switch Combo Switch #84310-08060 costs about $400.
Clean combination switch bearings
Once you get access to the combination switch, use a light rust penetrant solvent like WD-40 to dissolve the old grease and clean the rust off the ball bearings. If you get the bearings clean, you can regrease with white lithium grease and reinstall. Check for ground again. If that works, you’ve fixed the problem.
Jury rig a hardwired ground connection for the horn switch
Find the horn switch to combination switch wire and splice an additional length of wire to it. Route the wire down the steering column and locate a clean metal grounding screw under the dash. Test. If it works, reassemble.
©, 2020 Rick Muscoplat
Posted on by Rick Muscoplat