C5 brake errors

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db1
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Joined: 07 Mar 2010, 09:07
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C5 brake errors

Post by db1 »

Had an oddity with my "German" C5 auto petrol yesterday.

Drove to the supermarket. Started car and could not get it out of park. Then when it did come out as I moved off I got a handbrake error followed by ESR and ABS errors.

Stopped and played a bit and found:

1) The relay that lets you get it out of park was not always clicking when the brakes were depressed. Hence not coming out of park.

2) With the ignition on but the engine not running, trying to release the handbrake gives a "must have foot on brake" message after several on/offs. I assume that pressure had gone and that the switch that tells the handbrake the footbrake is on is different from the one that tells the gear lever the footbrake is on and it can move. The pedal also goes
solid at this point.

Now this is about 50 miles *after* it had been in for service Hmm.......

As a WAG I checked all the fuses were seated in the big box behind the battery and in fact they all went down a fraction. I can't see any dangling plugs (On the assumption that the service disturbed something).

After all this the fault still persisted. With a running engine I had the ESR and ABS lights on and the dashboard "check" button showed the same plus handbrake fault and rollback fault.. However with the engine stopped it showed no fault so I assume it only shows faults that are apparent when pressed. ie no history.

Anyway after stopping and starting a lot of times *and* working the handbrake by hand including "maximum" pressure it suddenly started clean and stayed that way on several starts.
C5 III petrol auto
wheeler
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Joined: 21 Sep 2002, 19:07
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Post by wheeler »

Sounds like a faulty or poorly adjusted brake switch to me. do the brake lights come on & off normally ? dont take that if the do work there is no fault with the switch as there may be two.
I guess its still under warranty ?
db1
Posts: 6
Joined: 07 Mar 2010, 09:07
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Post by db1 »

Thanks for the suggestion. I take it they are up under the dash somewhere above the pedals?

Yes still under warranty :-)
C5 III petrol auto
wheeler
Posts: 6848
Joined: 21 Sep 2002, 19:07
Location: United Kingdom
My Cars:
x 717

Post by wheeler »

If its the same as the mk1 & 2 the switch(es) are on the brake linkage up behind the glovebox rather than at the pedal. Located where the pedal would be if it was a LHD version. It may be a dual function switch with 4 wires rather than 2 seperate switches.
db1
Posts: 6
Joined: 07 Mar 2010, 09:07
Location:
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Post by db1 »

Found it - before I read your reply :-)

Only looks like one switch. Did not think to count the wires :-(

Anyway, so far, still clean. Think it goes on the "wait till it happens again" pile.
C5 III petrol auto
db1
Posts: 6
Joined: 07 Mar 2010, 09:07
Location:
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Post by db1 »

Oh well :-(

Went again in the Customs shed at Folkestone! But good luck in that it did not fail on the shuttle.

Up till now the errors had only shown up after trouble getting out of park. But on the trip they just came on whilst driving. Took it to a dealer in Germany who plugged in a lexia and said "brake switch". Changed under warranty in a few minutes.

What a *totally* different experience to the UK!
C5 III petrol auto
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