Why is my Maruti Brezza's horn behaving erratically at 40+ km/h speeds?

Since the horn works fine when the car is stationary, the guys at the authorised service centre said everything is in order.

BHPian BoneCollector recently shared this with other enthusiasts.

My Brezza turned 6 on 4th May. Lately, I've been facing an extremely strange issue with its horns.

Brezza has a dual-tone horn setup. One of the horns was changed in January 2021 post accidental damage. Both were working fine since then. For a couple of months, one of the horns is working on and off. I thought it was some connection issue so removed the bumper and secured it again. The issue persisted.

Then I started noticing the peculiarity. The horn would behave normally in city limits but then switch to a single tone once on the highway. Then I started to keep an eye on it and noticed that once the car would cross a speed of 40kmph, the horn would turn to a single tone.

Yesterday I tried crossing the yellow rumble strip at around 60kmph and kept pressing the horn pad, the second horn did sound for a second but then it was again single tone.

The workshop guys had also checked but since both the horns work when the car is stationary, they said it's fine. I've informed them again and will get it checked when I take it for service sometime next week.

The battery of the car was changed in December last year.

What could be the reasons for this behavior?

Here's what BHPian vigsom had to say about the matter:

Stock horns on most cars (except famed Densos on older Toyotas) start acting up after 3-4 years of use. I've seen this on a 2010 Altis (stock Roots horn), my own Versa (Padmini make MGP horn), and on the 2008 and later Honda Citys to name a few. Between the low tone and the high tone, it is almost always the high tone that packs up.

The issue is most likely due to contact points have gotten worn out. However, there is also an adjustment screw on the outside of the horn which can provide some relief. In stock horns like MGP, this screw is sealed using silicone sealant so that someone doesn't disturb the setting. In aftermarket horns, the screw is not sealed.

Adjustment screw (circled in blue) to make a non-functional horn work

I faced the same issue with aftermarket horns on my car. These horns cost no more than ₹700 a set, but me being me, decided to just open the erratic horns to see what was wrong. After spending approx. 45 minutes servicing the horn and putting it back, the issue resurfaced after two days and then I decided not to spend any more time on it.

The high tone horn

Horn opened up - diaphragm, body, and the "paam paam" air path

Horn diaphragm

Horn internals with the contact points shown - upper contact on the adjustment strip and lower contact on the horn

Horn internals - note the adjustment strip on the top

Horn adjustment strip contact pitted

Lower contact point inside horn carbonised due to sparking/long use

Horn contact after cleaning - note the pitting

Horn internals after cleaning

Here's what BHPian SS-Traveller had to say about the matter:

The contact point of one of the horns has likely pitted and almost burnt out. Replace the horn and the issue should disappear.

Here's what BHPian scorpian had to say about the matter:

Seems like a contact issue in the wiring. It would be best to trace all the way from the start point to the horn relay in the fuse box, somewhere there is a loose connection.

Another way out is to buy a hella horn wiring kit and bypass your existing wiring kit totally, this will sort out your wiring related issue plus you will have independent relays to use higher capacity horns.

Check out BHPian comments for more insights and information.