The van (iveco daily, sorry don't know the type anymore) of my father has a brake warning light on. Once I removed te cover I saw it was a single wire that was disconnected from the switch. I thought ok easy fix but when I connected it back the light was still there. Also a strange thing was ... when the switch is open I only have something like 3 volts which seems very odd. Could it be that the brake fluid sensor is faulty? I don't have any wiring diagrams so not sure if those are in series. However 3volts is odd maybe a break in the + cable?

So to conclude the wire was not connected and the brake warning light was on. Once I connected it it was still on no matter if I pressed the switch or not. If I push the sensor (open circuit) I measure only 3volts.

A subquestion (sorry for that) is how does the signal of a brake fluid sensor actually looks like? Is it also like switch or does the sensor acts more like a variable resistor? The sensor is a two wire sensor. And can I bypass it with a small resistor to check if the sensor is faulty?

Thanks in advance

  • Welcome to Motor Vehicle Maintenance & Repair! Is there enough brake fluid in the master cylinder? Did you check the e-brake as well? Any one of these can cause the brake light on the dash to come on. Mar 7, 2021 at 23:35
  • Hi Paulster, the brake fluid reservoir is full and on his there is no e-brake.
    – John
    Mar 8, 2021 at 18:15
  • Letting us know what the year/make/model of the vehicle in question could surely go a long way. If there is a sensor in the master cylinder for fluid level, make sure it is not stuck in the down position, which would show there's less fluid than actual. Mar 8, 2021 at 20:03
  • Sorry for my late respone Paulster it is an inveco daily 35s15 from 2011. There is a two wire sensor on top (integrated on the cap). Didn't had the time to check the float yet. I was wondering how the sensor works actually
    – John
    Mar 12, 2021 at 16:15


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