2016~2023 Brake light on, smart city brake malfunction, front radar malfunction - solved

Recently the brake dash light would come on when the car was first started, followed by the smart city brake malfunction and front radar malfunction warnings. This occurred intermittantly over several days. The warnings worsened, to the point that they remained on throughout a drive. Checked the usual suspects - camera issues re fogged windscreen, etc. Problem soved by the dealer. My brake pads were worn to 4 mm. The wear of the brake pads causes more brake fluid to pass from the reservoir to the lines to the point where it was below the fluid sensor in the reservoir.
 
I have never heard of anything like this happening before due to brake pad wears. Hopefully someone with better knowledge of brake systems will chime in, but I feel like if the issue was really low brake fluid level, then the fluid level was either too low to begin with (improperly filled) or you have a fluid leak somewhere. I recommend you keep monitoring your brake fluid level to make sure it doesn’t go down and you don’t have a leak.
 
I had the same lights come on yesterday. I’m at about 72k mi on original pads & rotors. I know that I need to replace at least the pads very soon.

The Smart Brake System Malfunction light came on first. It went on after I parked, shut the car off & turned it back on. A few hours later on the way home that warning came back on with a low brake fluid warning in the infotainment screen warning guidance & Front Radar Sensor System Malfunction. It also said Smart Brake System Malfunction.

I’m thinking it’s a combo of worn pads and low brake fluid. It just struck me as odd that the radar system warning would come on with the other ones. It was especially cold at 9° or so. The radar light came back on after a car wash so I know it wasn’t road grime/salt causing that.
 

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Also, maintenance rookie question here…

Can I just add brake fluid to the Mazda without doing anything else? I plan to get the pads replaced soon. Adding brake fluid now doesn’t cause a problem for that service, right?
 
Yes, a problem. As the pads wear normally the caliper pistons extend farther out toward the rotor. 100% normal. As the pistons extend farther out more fluid moves out of the reservoir and into the calipers. When new thick pads are installed the pistons are pushed back into the calipers. This moves fluid from the calipers back into the reservoir. There must be room in the reservoir for this fluid.

If the fluid level is very low, add a bit and get the brakes fixed right now. It should never get very low. When you replace the pads also replace the fluid. Fluid absorbs moisture from the air. It needs to be flushed and renewed every few years.
 
Yes, a problem. As the pads wear normally the caliper pistons extend farther out toward the rotor. 100% normal. As the pistons extend farther out more fluid moves out of the reservoir and into the calipers. When new thick pads are installed the pistons are pushed back into the calipers. This moves fluid from the calipers back into the reservoir. There must be room in the reservoir for this fluid.

If the fluid level is very low, add a bit and get the brakes fixed right now. It should never get very low. When you replace the pads also replace the fluid. Fluid absorbs moisture from the air. It needs to be flushed and renewed every few years.

That’s about what I was thinking. Just top it up a bit now to keep things working and have the fluid flushed when I get the brakes done. Thanks for the reply!
 
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