Peugeot 406 Brakes

Avocet said:
Yes, it absolutely should. However, to do it properly, you need to exhaust the servo first. With the engine not running, press the brake half a dozen times. The servo itself (and the tubing to it) will store some vacuum for a while after shutting the engine down. The intention is that if your engine stalls, you will still get a few brake applications before you run out of servo assistance. Pressing the pedal half a dozen times without the engine running, will use up all that vacuum and the pedal should end up feeling pretty hard.

At that point, rest your foot on the brake pedal gently and start the engine, within about a second of startup, you should feel the pedal sink under the weight of your foot.

That indicates that the servo and the vacuum pump (if it's a diesel) are working correctly. However, it doesn't confirm anything about the state of the master cylinder. In days gone by, you used to be able to press the brake pedal really hard, and a slow sinking of the pedal meant either master or wheel cylinder problems. However, on some ABS-equipped Peugeots, (and other marques), I have noticed that the pedal will sink slowly under those conditions anyway - even on a new car.
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Thank you for that. The principle makes sense, so I'll have a go. I'll do it on a cold start tomorrow.
 
Bit of an update on this problem (car slowing down and brake lights coming on). I have been told that a faulty brake light switch can cause this issue and since searching the issue with different keywords, I have found a multitude of different contemporary cars from the PSA group with the same problem.

Basically, as the throttle system is a 'fly by wire' set up, the BSI will lower the engine speed if it detects braking. This is to prevent the a dangerous situation should the car's throttle 'run away' and the driver need to stop the car. I think fuel cut-off is also connected.

I am going to source the right switch (mine field of different types out there) and hope this solves it. I have noticed that whenever it has happened, taking my foot off the throttle and then back on again has temporarily relieved the problem. It makes me think the servo is okay as the brakes are generally fine otherwise.
 
If anybody is interested, I solved this problem.

Took the drivers seat out and lay down in the footwell to get to the switch. The mechanism in the old one was a little worn and when the brake pedal was returning to its 'home' position, it wasn't always engaging with the switch. A new one put properly into position has solved this problem and the car no longer slows down on its own!

Great with a pending drive to Devon and back next week.
 
Absolutely! It was a big relief to have finally solved it. That and a now non-leaking thermostat housing gives me plenty of reason to keep the car working and being serviced!
 
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