Volvo VNL Highway Horn Not Working? Here’s How to Fix It
If your Volvo VNL highway horn is not working, don’t start replacing parts right away. Most of the time the problem is something simple like a blown fuse, a bad highway horn switch, or no power reaching the air valve.
Below I’ll show you exactly how I diagnose it before spending money on parts. Start from the first step and don’t skip anything because many times the problem is found within the first few minutes.
Step 1 – Check the Fuse
The very first thing you need to check is the fuse box.
Some Volvo VNL models have a fuse for the highway horn and some don’t. It depends on the model year and configuration.
Open your fuse box and inspect every fuse related to the horn. If you find a blown fuse, replace it and test the highway horn again.
Some Volvo VNL trucks don’t have a dedicated highway horn fuse, so don’t panic if you can’t find one. If everything looks good, continue with the next step.
Step 2 – Locate the Highway Horn Solenoid
Now go underneath your truck.
Right behind the transmission, close to the air dryer unit, you’ll find a Solenoid Switches. This switches controls several air-operated functions including:
- Highway horn
- Suspension dump
- Fifth wheel slider lock
- Differential lock
This is the solenoid switches we need to check.
Step 3 – Which Switch Is for the Highway Horn?
You’ll notice there are four or sometimes five electrical plugs connected to this solenoid assembly.
If you’re wondering which one is for the highway horn, don’t worry. We already marked it in the picture below.
Facing the valve assembly, the very first switch on the left is the highway horn switch.
Step 4 – Test the Steering Wheel Switch
Now remove the 1/4-inch push air line from the highway horn valve.
After removing the air line:
- Make sure both air tanks have at least 80 PSI.
- Go inside the truck.
- Press the highway horn switch on the steering wheel.
Listen carefully for air coming out of the solenoid.
If you hear air leaking loudly, then most likely your horn itself is bad.
The highway horn is located on top of the battery box. Find it and replace it if necessary.
Don’t forget to make sure both air tanks have enough pressure before doing this test. Less than 80 PSI may give you incorrect results.
Step 5 – No Air Coming Out?
If there is no air coming out when you press the highway horn, then the problem is somewhere before the horn.
Usually it’s one of these:
- Bad solenoid switch
- No electrical power reaching the switch
- Damaged wiring
Remove the electrical connector from the switch and use a test light or multimeter.
You’ll need another person inside the truck to press the highway horn switch while you check for power.
If there is no power, start tracing the wiring.
If power is present but the switch still doesn’t send air, then replace the solenoid switch.
You can’t replace only the individual solenoid switch. The switches are part of one complete solenoid assembly, so you’ll need to replace the complete unit.
Step 6 – Make Sure Air Supply Is Reaching the Valve
One more thing before replacing anything.
Use the suspension down switch on the dashboard.
If the suspension goes down normally, then air is reaching the valve assembly.
That means your air supply is good and you can continue checking the electrical side.
If power is coming there then replace the horn and it will start working.
Final Thoughts
Most Volvo VNL highway horn problems are caused by a bad switch, solenoid, wiring issue, or a failed horn itself.
Start with the easy checks first. Verify the fuse, locate the valve assembly, test for air, check for power, and only replace parts after you’ve confirmed they’re faulty.
Following these steps can save you a lot of time and money instead of replacing parts that aren’t actually bad.
Frequently Asked Questions
Why does my city horn work but my highway horn doesn’t?
The city horn and highway horn use different systems. If the city horn works but the highway horn doesn’t, the problem is usually the solenoid, steering wheel switch, wiring, or the air horn itself.
Where is the highway horn solenoid located on a Volvo VNL?
It’s located underneath the truck behind the transmission, close to the air dryer unit. This solenoid assembly also controls the suspension dump, differential lock, and fifth wheel slider.
Where is the Volvo VNL highway horn located?
The highway horn is mounted on top of the battery box. If air reaches the horn but it doesn’t sound, the horn itself is likely faulty.
Can I replace only the Solenoid?
No. The solenoid is part of the complete assembly. If the switch fails, you’ll need to replace the entire assembly.
How much air pressure do I need to test the highway horn?
Make sure both air tanks have at least 80 PSI before testing. Low air pressure can prevent the horn from operating correctly.
