Brake switch failure code P0571 blocking use of cruise control

Hi Citroen owners,
I have a problem that is blocking use of cruise control. I get error P0571 from time to time (it appears and dissappears randomly).
I saw in LEXIA that the problem is main brake switch. I made a screenshot when brake pedal was pressed.
Is there any post about braking electrical loops? Did anyone work with wiring to this pedal?
Best regards

C3PO_Furio wrote: ↑Thu Aug 24, 2023 7:28 pm Is there any post about braking electrical loops?
Best regards

Hi

Ignore the bit about the loop being closed, it's not relevant to the fault.

Change the redundant brake switch, or to be sure, change them both.

The brake switch has 2 sets of contacts in it.
One set powers the brake lights, the other goes onto the CAN BUS. The CAN BUS contacts tell the CAN BUS items (autobox, engine ECU, ETC) that the brakes have been applied.
When one set of contacts are open, the other is closed (and vice versa) which is how the BSI knows that there is a fault. If one set changes state but the other doesn't...then there's a problem.
For a right hand drive car the switch sits up under the glove box on top of the brake pedal torsion bar support.
You can get replacement switches from Ebay cheaply enough BUT you need the "white" one, NOT the "green" one.

Hi Ozvtr,
This is a wrong statement.

Ozvtr wrote: ↑Thu Aug 24, 2023 9:51 pm The brake switch has 2 sets of contacts in it.
When one set of contacts are open, the other is closed (and vice versa) which is how the BSI knows that there is a fault. If one set changes state but the other doesn't...then there's a problem.

The topic is a little bit more complicated.
The green element contains 4 contacts - 2 switches. One switch is for braking light - normally open switch (NO) and the other one used for cruise control is a normally closed (NC) switch.
The white element has 2 contacts - 1 switch. This switch is normally closed (NC).

The braking light switch is indeed a normally open switch. Braking light switch is part of green element.
I bought it under PSA number 453465 / 4534 65 / 4534.65.

Location of both braking switches is presented below: Real life location on LHD vehicle is preseted here:

My apologies.
My statement is for a Right Hand Drive car. I did not realize your car was Left Hand Drive. Sorry.
However most of my statement is still correct.
You can remove the switch and test it independently against LEXIA to check. You just turn it 90' and slide it out (if you have replaced the switch then you know that). Press on the brown plunger and monitor switch status in LEXIA (main brake switch and secondary brake switch). This will prove that both brake switches are in the one device.
The brake switch is identical in a RHD car but colour coded white. Again, both sets of contacts in the one switch are used for braking functions.
The "green" and "white" brake switches are not interchangeable. My son has the "green" switch in his C4 (RHD). Don't ask me why the green and white brake switches are not compatible when the function and operation is identical. (?) The keyways on the electrical connectors are different!

The "white" switch in your car (labeled 7306) is the clutch switch, this is not just dedicated to the cruise control. It also tells the engine ECU that you are disconnecting the engine from the drive line. It's actually a light grey colour. It is a completely different shape to the brake switch and clips onto the side of the pedal box. You can monitor that switch in LEXIA (clutch pedal switch status) just depress and release the clutch pedal. Of course the clutch pedal switch is only used in a car with a manual transmission.

EDIT: Added "main brake switch and secondary brake switch" to note in LEXIA fields.

Just as an aside, the second LEXIA box ("parameters") tells you WHEN this occurred. It's not much help as the parameters are only relevant as to what the engine was doing. But this is what it means;
The "Permanent fault, redundant brake switch switch signal Problem" is code P0571. The switch is redundant because there are 2 sets of contacts (a "redundant set" of contacts).
The engine was doing 1073 RPM. Marginally above idle.
The coolant was 70'C. So I would guess this was the first stop after starting the car that time. If the engine was fully warmed up it should be aprox 90'C.
You were only doing 16Kph, so I guess slowing for a stop (or something like that)?
Inlet manifold pressure shows the throttle closed engine running. Throttle fully open, about 1000 mBars.
Mixture adjustment state shows engine in closed loop mode and reading data from Oxy sensors.

Another interesting fact is; a failure of these contacts in the switch will cause the gear selector in an automatic car to lock in park. To get the selector out of park requires the driver to put their foot on the brake. This switch contact is connected to both the engine ECU (like a manual) and the auto ECU in an auto.

Hi Ovztr,
Thanks for your anwser, you are right, that I made a mistake and confused cluck and brake switches.
I looked inside brake switch (in my car it was green) and it is really straightforward design. It is surprising for me, that this switch failed.
And it sounds crazy for me, that LHD and RHD cars have different colours of switches... But it sounds like PSA design :p

I have a C3 RHD with an AL4 gearbox and the car is second hand.
When I first got the car the selector would some times lock in park.
I tracked the fault down to the brake switch (with the help of LEXIA).
The contacts of switches and relays must have a certain amount of current flowing through them or they will oxidize. This is called wetting current. Oxidization causes resistance. The 'Primary' contacts of the stop switch power the rear stop lamps and plenty of current flows through those contacts. However the secondary contacts have very little current flowing through them and so they oxidize.
It's possible to pull the switch apart and give the 'small' contacts a rub with sandpaper.