Hi all.

 

The brake warning light is on in my Felicia. The brake fluid was a little low so I have topped that up but the light remains. I (well actually DaveRapid did!) unplugged the sensor from the brake fluid tank and the light remains on. What else could it be? 

 

The brake pads are okay for what it is worth, but don't have sensors on them anyway. 

 

Thoughts?

I though disconnecting the sensor will cause the light to come on because you have made the car think the fluid is low, it could just be a duff sensor.

Could a piece of grit or something have got into the reservior, and hence into a capillary level measure, or doesn't the sensor work like that?

the brake fluid level sensor is in the cap of the brake fluid reservoir, its basically just 2 electrical contacts which go to a plug, the brake fluid makes the circuit which makes the light go off..

 

try unplugging the cable from the sensor and bridging the contacts on the plug with a hair pin and check that the lamp goes off.

the brake fluid level sensor is in the cap of the brake fluid reservoir, its basically just 2 electrical contacts which go to a plug, the brake fluid makes the circuit which makes the light go off..

 

try unplugging the cable from the sensor and bridging the contacts on the plug with a hair pin and check that the lamp goes off.

 

according to you the schematic looks like in the drawing below.

the brake fluid acts as a conductor, right?

so how it's possible to have the warning light off with enough fluid??

or with the cap off and shorted electrodes??

the warning light should be on!

I'm not entirely sure what I have done but the light has gone off. Huzzah!! 

the brake fluid makes the circuit which makes the light go off.

not true.

brake fluid has low conductivity (high resistivity).

try unplugging the cable from the sensor and bridging the contacts on the plug with a hair pin and check that the lamp goes off.

wrong advice, see why.

on most cars (including Felicia) the brake fluid level switch is using a float tied to a vertical rod that has a copper disc at the top end (see drawing)

when there is enough fluid in reservoir, the copper disc is pushed up, away from the two contacts.

when the fluid level is low, the float goes down and the copper disc shorts the contacts, thus lighting the warning lamp.

 

the OP had a classic case of stuck float in down position due to debris.

the long term solution is a thorough cleaning of the float/cap assembly 

changing the brake fluid helps too.

yes you are quite right, i was thinking of the coolant level sensors, the brake fluid sensor is the opposite logic state, but some vw's use a resistive measurement where both side of the sensor is live and it attempts to measure the fluid resistance to check how clean it is by measuring the voltage drop.

i was thinking of the coolant level sensors, the brake fluid sensor is the opposite logic state

 

although Felicia doesn't have one, the coolant level switch is using the same principle of operation and logic as the brake fluid level switch.

although Felicia doesn't have one, the coolant level switch is using the same principle of operation and logic as the brake fluid level switch.

 

mines has one, its a retro fit from a 6k ibiza, i thought it was necessary seeing as i've popped hoses in the past. the vw ones are literally just 2 metal contacts moulded into the plastic expansion tank

 

the OP had a classic case of stuck float in down position due to debris.

the long term solution is a thorough cleaning of the float/cap assembly 

changing the brake fluid helps too.

 

 

Had this problem myself recently after new brake pipes were fitted. Fluid needed minimal topping up and the handbrake light was still on; back off with the cap, jiggled the float, and bingo!