Hesitation Cured by Brake Switch

[BX]

Most makes that have fly by wire accelerators sense the brake activation and use it to limit fueling and or rpm. This is in the interests of safety. You do not want the vehicle to be trying to accelerate due to a faulty or stuck accelerator pedal whilst you are trying to slow down and applying the brake.
The fuel cut off on over run is a separate and is an economy measure. Fuel delivery is stopped if rpm is over a threshold figure and the accelerator pedal is released.

[Paul-R]

Now that makes sense.

[AviSa]

Marc,

I'm having similar problems with C5 2L 2005 RFJ. Can I verify the problem you described by monitoring the break lights?

i.e. does the brake lights remain on even when the brake paddle is not pressed with a faulty brake switch?

Thanks

[GiveMeABreak]

Marc,
I'm having similar problems with C5 2L 2005 RFJ. Can I verify the problem you described by monitoring the break lights?
i.e. does the brake lights remain on even when the brake paddle is not pressed with a faulty brake switch?
Thanks

No, that certainly wasn't the case with ours. The brake lights worked fine - but relatives have a Xsara Picasso 1.6 HDi and that has started hesitating whilst running a few days ago, mostly in 5th, but now in all gears. It is booked in tomorrow as they suspect that that also might be the brake switch issue (it has the cruise too).

I've seen you other post - so I'll respond there regarding that.

[BX]

As far as I can see all vehicles with fly by wire accelerators use a brake switch input to the ECU. It fulfils a major safety function. Should there be a fault or spurious signal from the electronic accelerator which causes the car to accelerate, the drivers natural reaction is to press the brake. Fuelling and therefore engine power is limited, helping the brakes to slow the vehicle. Also the maximum rpm is often limited. I first encountered this on VW cars.
Secondly cruise control is no longer implemented as a separate physical system but is incorporated into the body, engine and transmission ECUs. The brake input suspends the cruise control. Often both outputs from the brake switch are connected to the ECU in the interests of safety.

[Paul-R]

OK, that does make sense. Ta.