Brake fluid is hygroscopic and will accumulate water over time despite being in a nominally sealed system. Water in solution with brake fluid noticeably lowers the boiling point which leads to issues under repeated braking (e.g. down long steep hills) as the fluid boiling means you lose braking capacity in that circuit.

You should ideally be changing the brake fluid every few years (2-3 being the typical recommendation) and that applies even if the brakes are used less often.

You can use DOT 5.1 to significantly increase that wet boiling point, but it's expensive for normal car use. I usually use it in my motorcycle, since I've experienced brake fade on that before, and it's... Not fun.

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This is a reactionary response, you're just arguing, slow down a bit.

Do you see a value in a check engine light that tells you something is wrong in between full inspections? This is similar, this is telling you there isn't enough oil and damage is occurring before you get a chance to inspect the dipstick.

It's not planned obsolescence unless they also make it unreasonable to service. We already expect to routinely service engines, and they are already very complex and full of sensors, sure this is adding to the complexity but it's relatively pretty minor.

The argument being made, and I agree with it, is that the benefits of an additional long-serving sensor way outweigh the con of having one additional sensor in your car. You get early warning before damage occurs, you get built in fraud protection when you're changing your oil at a shady chain, you eliminate a direct access port for dirt to contaminate the oil.

DOT 5.1 to significantly increase that wet boiling point, but it’s expensive for normal car use

Huh? In here you can get DOT5.1 for the same price than DOT4. Roughly 10€ per litre, depending on brand and how big bottle you get.

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friend of mine had a ford like this. and it cost more than the car to fix after only 10-15ish years of use. its terrible.

Yeah, that's just how it goes as the engine becomes more complex, leaving a dipstick there is not gonna change that...

My wife has a 2016 Honda Odyssey, and having grown up working on cars because my dad was a mechanic, I was shocked to learn that there is no transmission fluid dip stick. It's considered a closed system and never needs to have the fluid changed, allegedly.