Mysterious problems

Questions not related to the fuel type, like Manual Gearbox, Body Work, Lights, Interior trim and Seats, Steering, Brakes, Beeping, Wheels and Tyres to be asked in this topic only.

Audio has its own section - see further down the page.

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My Name: Ozvtr

Moderator
Posts: 956
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
Has thanked: 37 times
Been thanked: 256 times

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Andreasautumnus wrote: Wed Jul 28, 2021 3:35 pm Next step in my mind would be to move to harness and one wire in particular. Nr 12 (yellow) in engine fuse box 16 pin green connection leading power to cruise control brake (red) and clutch (grey). All the earths seem ok.
FYI. A problem with the brake switch will throw up a "coherence" fault. There are two sets of contacts that change over when actuated. One set open when the other is closed. Both open or both closed at the same time causes a fault. One set is monitored by the engine ECU (and the auto box), the other is monitored by the BSI (for the brake light circuit).
My Name: Andreasautumnus

Contributor
Posts: 13
Joined: Sat Jun 06, 2020 6:23 pm
Model: C3 2002-2005, Original shape model
Year: 2002 (02)
Engine Size: 1.6 i
Fuel Type: Petrol
Mileage: 125000
Trim Level: VTR+
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: LHD (Europe)
Been thanked: 2 times

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Was the power wire from engine fuse box to pedal switches that was in poor condition (copper exposed in multiple wires near it). Some readjustment of wires and electrical tape sorted it out. Runs smoother now also... weird issue thats hard to pinpoint but at least made me analyse all the sensors and other components and found even some unreliable ones.

I also heard some experiences where clutch pedal switchs plastic holdings were slightly broken giving similar issues.
User avatar
My Name: Ozvtr

Moderator
Posts: 956
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
Has thanked: 37 times
Been thanked: 256 times

Post

That should have thrown up a coherence issue but being transient maybe not? I'm not sure on that one.
My Name: Andreasautumnus

Contributor
Posts: 13
Joined: Sat Jun 06, 2020 6:23 pm
Model: C3 2002-2005, Original shape model
Year: 2002 (02)
Engine Size: 1.6 i
Fuel Type: Petrol
Mileage: 125000
Trim Level: VTR+
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: LHD (Europe)
Been thanked: 2 times

Post

I was suprised too that no error was present. Weirdness in wires was after the brake switch power supply so that was always getting power. Only clutch switch was affected. Also gave roughness in idle and at lower rpm while driving. Of which i am unsure what is the cascading failure there... most likely caused by ecu adjusting firing of coils in a slightly weird way. (Only weirdness found while looking parameters with lexia) was in a really painful place to sort out the harness issue..
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