Hesitation Cured by Brake Switch

[GiveMeABreak]

Well another problem attributed to and cured by replacing the Brake Switch on our C3 1.6 HDi today. It's only done 38k miles in it's 9 years!

The car was occasionally hesitating whilst going up hill and spluttering over the last 2 weeks. I ran Lexia on it and it came back with the Glow Plug Relay fault - but I was told could be a ghost issue - and more likely to be the Diesel fuel filter. It was due for a service today at the Main Dealer - so went in for investigative on this issue at the same time. On the way to the garage doing about 50mph in 4th, I got a flat spot, which took a little while to recover.

It turned out that it was the good old Brake switch! So not only does this little box of tricks affect the ABS / ESP / Cruise/ Speed Limiter/ EBA / EBD systems (oh, and of course the Brake Lights!), but would seem to influence the injection system too! Driving it back the car was so much more responsive - no hesitation, and no flat spots. Overtaking made a heck of a difference too - just seemed so more responsive.

Although this was on a C3, I suspect could also be relevant on other models and thought it worth a mention for others - could save some time and money playing about with glow plugs, relays & injectors!

[white exec]

Just out of interest, how complicated is this brake switch?
Just one set of changeover contacts (make for brakes, break for cruise), or something more complex?

[myglaren]

At least on the C5, the fuel is cut off if the brake pedal is pressed and I imagine the same is true of other models in the range.
So it isn't really surprising to find a buggy brake switch interferes with the fueling.

[paultintin]

On the c4 grand picasso it's located under the glove box behind a little cover held in place by a couple of screws. It's really easy to change just twist 90° then unplug the electrical cable I paid less than £20 for a new one with a small extension cable as the leads are very short. Just remember to measure the length on the green part against the main body and push the new one in to the same length. I did have some pics if I can find them will put them up

[GiveMeABreak]

Just out of interest, how complicated is this brake switch?
Just one set of changeover contacts (make for brakes, break for cruise), or something more complex?

Well it's certainly the make & Break twin function switch, given that it has Cruise/Limiter - but looking at the Wiring diagrams, I'm at a loss to find what "Z013A, B or C" is as it isn't returning anything under the equipment or wiring for these codes - which I can trace to the Engine Fuse Box and the BSI - but from there on it's a mystery!

[GiveMeABreak]

At least on the C5, the fuel is cut off if the brake pedal is pressed and I imagine the same is true of other models in the range.
So it isn't really surprising to find a buggy brake switch interferes with the fueling.

Good point - never thought of that.

[frogdr1ver]

Out of curiosity how did they diagnose it was the brake switch if it wasn't showing up in lexis?

[GiveMeABreak]

Probably from experience, I've been using the same technician for 25 years, who is now the Service Manager and he knows all the quirks! Lexia can only go so far, if it was infallible, it would simply say "Replace the Brake Switch" . There's a lot to be said for experience.

[white exec]

Now I understand. So, effectively, the brake pedal switch is part of the fuelling system. Presumably diagnostic procedures for the fuel system will list it in the checks to be run.

[Paul-R]

Marc, where did you get the information that the brake switch has an input to controlling the fuel? I actually find that hard to believe as I can't understand the rationale. I can't comprehend a situation where that would be needed that isn't covered by, for instance, cutting off the fuel on the overrun.

[GiveMeABreak]

Direct from the Service Manager - they rang me up mid-day for permission to change it and that this was the fault - later on I caught him and he mentioned that this can affect the injection system if faulty. Don't shoot the messenger guys - here's an extract of the invoice with the problem and the fault:



So from a week ago when I ran a diagnostic on it, there could well of been another fault that developed or the existing fault worsened by yesterday. It was a bit hectic there yesterday and I was also solving another mystery as to why I kept being asked to book my X7 in for service when it has only done 4k since last July when it was serviced! - Turned out the last chap that booked it in mistakingly used my reg. number (private plate) - which I had transferred to my X7 from my 2005 C5 Exclusive! So they had my old car I no longer have down for the service that was done on my X7

[white exec]

Presumably brake pedal fuel cut-off/reduction is just one more means of slicing another whisker off the fuel consumption figures.
Can see the point Paul is making about cut-off on overrun, though. Interesting.

[xantia_v6]

It could be to cope with drivers who keep their left foot on the brake and operate both the accelerator and brake at the same time. I have seen a few of those, particularly in Asia.

[Gibbo2286]

It could be to cope with drivers who keep their left foot on the brake and operate both the accelerator and brake at the same time. I have seen a few of those, particularly in Asia.

I've seen a few of those here too, usually when they're crying that their auto box has died prematurely.

[frogdr1ver]

The reason I asked how they knew was it was something the local dealer suggested when my c4 started hesitating at pulling away which all started after a turbo replacement. The garage that did the turbo replaced it (I'd replaced it about a year earlier) and it didn't make any difference.