I’ve owned my Mazda 3 for just under 2 years now. On cold, damp days I often find that a number of warning lights come on, related to lane guidance (Lane Departure Warning System – LDWS), automatic full-beam (High Beam Control System – HBC) and automatic braking (Smart City Brake Support – SCBS). After a while, the warnings clear.

But, yesterday, I had the same warnings come on but the lights didn’t go out, even after stopping and restarting the ignition.

How to fix it

The usual cause of this problem is that the windscreen is wet, frosted over or just misted. In this case, once the windscreen is clear again, you’ll find the warning lights go off.

In the case of yesterday, it was none of those. So I panicked a little – an electrical failure of some kind? When was I going to be able to get it to the dealership?

As it turned out it was something really simply…

This is a splat of bird excrement at the edge of the camera. A quick wipe and the sensor issue was fixed.

Now, all of these solutions are specific to this group of sensors. I’ve read elsewhere that if you just get warning lights related to braking, for example, then it possibly means there’s an issue with your braking system somewhere and possibly doesn’t relate directly to the particular braking sensors that are being warned about.

Why does this happen?

The reason why this often occurs is because wet, condensation or, yes, bird poop can get in front of the sensors – these are situated behind the rear-view mirror, looking out towards the road in front.

All of these sensors require a view of the road ahead (when to brake, when to raise the high beam and when you’re moving across lanes) and so when their view is blocked, you’ll see the warning lights.

I’ve read that earlier Mazda models used radar for detecting objects, which wouldn’t have been prone to this problem, but this was changed to cameras for improved capabilities (I’m guessing radar can’t detect a road marking!).