Brake servo on Yaris hybrid 2014

[barnonline]

I have a rather strange problem on my Yaris from 2014 TOYOTA YARIS (_P13_) 1.5 Hybrid (NHP130_) (75Hp)

The brake warning lights began to light up on the dashboard.

I could feel no difference on the brakes, -I have not tried to activate the ABS with a hard braking.

The brake fluid level is fine, and it is not leaking.

I took the car to an authorized workshop that told me it was the brake servo that was the culprit and that I would cost me 5600 Euro to get it fixed, and approximately half, if it was a used spare part. That seems excessive.

I had to give that some consideration….

Here comes the strange part: It is only a problem if the temperature is over approximately 5C, if it is colder than that, the lights turn off.

I have confirmed this with many observations, it is 100% certain that it have something to do with the ambient temperature.
This makes me suspect a sensor malfunction. Does anyone have a clue or hint?
 

[APS]

Might be a wheel speed sensor. I'd try braking hard to see if ABS activates as it should.

Also, did the garage read any ODB codes? That might give further clues. 

[flash22]

You need the exact code to pin point the issue, when was the 12v Battery last changed or is still on its original ?