So I drove 2 long highway trips this early week, and decided to give the car a full wash this morning.
After that, drove the usual 3 km uphill, then 5 km downhill back home.

During the downhill, I decided to perform some stronger braking, just to build some heat, and to clean the disks / pads from built-up from the normally relaxed and soft braking I do.

It went all well, brake performance came back after 3 times, only to have a 'low brake fluid' warning in the dash the 4th time.
But no drop of brake performance, no weak pedal, nothing.

I stopped, couldn't find a thing, and on the (slow) way back home, the message never came back.
Not even after some further heavier braking.

As it is the brakes, I kind of wonder / worry what the heck happened, and what I will need to do to either replicate the problem, or prevent it.

PS. No wash water in the engine bay or electrics, I am sure of that.

 

Tilt angle in the reservoir?

 

Have you got rubber flex lines to the caliper? Go braided if so.

 

I have never looked at it, but is it a float, or a contact kind of sensor in the reservoir? Do you know?

Ha, that makes sense ... maybe ...
I know braided lines from sportbikes, never thought about it for this car.
Guess they are still the original OEM.
I googled a bit for sets, but supply seems limited or out of stock.
Any suggestion for a set of 4?

 

I don't remember, but I think they are typically a float.

Don't see how a bulging brake hose is going to cause a low fluid alert, but those hoses do go bad overtime. My wife's Maxima failed an inspection a few years back; inspector said it was a bad caliper. So I buy a new caliper, bust some wrenches and hands getting the old one off, and while bleeding the system (wife is a real pro at pump, pump, HOLD), noticed the problem was a bulging hose . . .

 

Here's one
https://www.mtecbrakes.com/jaguar-xj...xoCS7oQAvD_BwE

 

Yup, that seems to be the set I saw 'Sold Out'.
Will order a set, guess changing some 20 yr old brake hoses is an healthy idea anyway ....

 

New set on the way, thanks for the replies!