DS5 Semi Auto 1.6 13 Reg

[Citroenmonamor]

My DS5 had a number of problems I had to get the Clutch/Flywheel changed, the drivers front ABS ring and sensor changed..I used a Lexia with Diagbox to diagnose the faults. I need to program the gearbox now but I have a P171a brake signal fault and although the car drives in manual I can't get auto and the brake lights staying permanently on. I did previously change the brake pedal sensor on the passenger footwell with a gm part with same part number. I have tried deleting the error codes but it comes back with the fault code. We did change the Geatbox ECU as the old one was faulty. Any ideas please

[RichardW]

If you've got Diagbox then check the status of the two signals from the brake switch. They should be the same and change together.

[Citroenmonamor]

How do I do that please?

[Citroenmonamor]

With continuity on the switch itself unplugged or on the wiring plug ?

[RichardW]

If you go into standard parameter measurements then you should be able to see the status of the two switches, and they should change together. However, I did a bit of a search on this code and it may in fact be related to the signal from the alternator. Is yours stop / start? Where did the replacement ECU come from?