Hi guys,

I recently noticed while driving that my glowplug (MIL) light blinks after driving for some time and when I press brake pedal, light goes away and returns after about 15 minutes without touching brakes.
I scanned for fault codes and I got this code:

 

1 Fault Found:
00741 - Brake Pedal Monitoring 
            27-10 - Implausible Signal - Intermittent

After a little bit of research I learned how to test both of the switches using VCDS.
As per THIS page, fields should read 000 when pedal is not pressed. My problem is that second bit always reads one like this:
 

0 1 0

When I press the brake pedal, the state changes to 0 1 1 but when I let go of the pedal, the state changes back to 0 1 0, which is incorrect. I tried unplugging the connector on the blue switch above the brake pedal but the state does not change, it still reads 0 1 0. Could my switch be faulty or is this a wiring issue ? 

Edit: switch looks exactly like this:

 

Edited 19 October, 20223 yr by LoOdaK
Edited picture

Okay so I got some free time and disassembled the switch. I cleaned the contacts in it and I think I figured out how it actually works and fixed the problem. I drew two illustrations to show inner workings and hopefully help someone in the future.

First of all, this switch is an NO (normally open) switch type which means when it is not actuated, switch contacts are open and do not close the electrical circuit.

 

 

After I assembled the switch I tested it with a multimeter and found out that the switch closes (shorts) it's contacts when the switch plunger is pushed almost to the end. This is actually logical because if you take a look at the first diagram and take a look at the contact strip, we can see there is a bulge of copper at the end of the switch. Switch actually works by sliding main contact above ridges which we can see on the front view illustration. Those ridges keep main contact from closing the circuit, but when the plunger is pushed all the way to the back, main contact closes the circuit.

Now to the fault code. What I found out is those switches need to be synchronized, which means when we press the brake, both readings inside VCDS should read 1. In the second illustration, I tried to illustrate how both of those switches should be mounted. I was adjusting my F47 switch and taking look at the VCDS to see when both switches will output 1. After some time I got it working, when brake pedal is pressed, both bits inside VCDS read 1 at the same.

I hope it will help someone in the future.