Brake light on dashboard

Is that the red warning light? Does it actually say "Fluid Level" or does it just say "Brakes"? It sounds like the parking brake warning switch is not adjusted correctly.

Hold the phone! The yellow ABS light means the computer detected a problem, set a diagnostic fault code, turned the system off, and turned the yellow light on to tell you. That fault code may be able to provide a clue.

If you found the float "died" in the reservoir, don't bypass the switch with a jumper wire, as it sounds like you may have done. Simply unplug that switch. If the light goes off, turn the ignition switch off, then back on. If the yellow light goes off after six seconds, it was on because the computer saw the red light was on. It wouldn't know why but it knows whatever is causing the red light to be on could prevent it from operating the ABS function properly, and that would be the only reason the yellow light was on.

This video can help you get the codes.

https://youtu.be/rTtAnsOlZU4

If the float is the issue, you must buy a new master cylinder for some car models. On others you can buy just the reservoir. You can also just leave the low-fluid switch disconnected. A lot of cars don't even have that feature. You just have to check the level periodically.

As a side note, when the brake fluid is low AND there's no external leaks, it is because the front brake pads are worn and ready to be inspected. As they wear, the pistons move out of the calipers. That is how they constantly self-adjust. Most of the time new pads are just installed, but the pistons have to be pushed back into the calipers to make room for them. That pushes all that brake fluid back up into the reservoir. This is why no conscientious mechanic will ever fill your brake fluid reservoir during other routine service, like oil changes. To do so would create a big mess from fluid overflowing later when the brake pads are replaced.

Hi there,

see if a scan shows up any problem, as for the brake light, this may just be a case of the brake fluid being a bit low, check and top up if required.

Mark (mhpautos)

A connection seems to be loose somewhere and this requires proper diagnosis to get to the bottom of it.

The brake lights are not linked to the MCU and are only conttrolled via the brake switch so I don't see any reason for them to come on except for a failed or misadjusted brake switch.

Are you sure it is the brake lights that is coming on orare they the taillights? They uses the same bulb except different circuit.

Is your vehicle hatchback or sedan and what is the engine size?

After replacing the MCU and you are getting the same problem so it means either the replacement MCU is also bad or it is something else.

I would not rule out the instrument cluster for the problem. It is equipped with a CPU that can cause the indicator light to com on or go out.

Did you use a scan tool to test the instrument cluster and check for trouble codes?
How about swapping the instrument cluster with your frined for a test?

Check the brake fluid level in master cylinder reservoir. If it is too low, the symptoms described would occur.