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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

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  • 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 at 23:35
  • Hi Paulster, the brake fluid reservoir is full and on his there is no e-brake.
    – John
    Mar 8 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 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 at 16:15

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