C4 Grand Spacetourer Parking Brake Fault

[lambie413]

Hi all

2018 C4 Grand Spacetourer 1.5 Blue hdi

Before Christmas my car started displaying "Parking brake fault: Have the vehicle repaired". The car was booked in for repair. Mechanic said the battery was knackered so he would change it and that would hopefully sort it.

After the battery was changed the car was great for a couple of days. Stop/start worked and no faults. The fault, however returned and start/stop stopped working.

The fault appears as follows:
1. Stopping at a junction green A flashes but the car doesn't switch off.
2. This will happen for one or two more junctions.
3. After pulling away from the second or third junction the yellow A off light flashes then remains illuminated.
4. Next junction I stop at "Parking brake fault: Have the vehicle repaired" appears and Serviced light is illuminated

I have done a scan with diagbox and have found fault u1208 81 appears in the ESP module and it P0806 82 Clutch master cylinder position sensor appears in the engine ECU after this fault appears on the dash.

Cleared both codes and took the car for a spin.

Start stop still didn't work. It was 4 degrees outside and the battery's SOC was only 70% (seems low to me).

No fault appeared for quite a long time. In fact I thought it was sorted until I was on my way home and the yellow A started flashing again. At the next junction the parking brake fault appeared on the dash again.

When I returned home both P0806 62 and U1208 81 had returned.

Any ideas what it could be? Should I be suspicious of the new battery being faulty or is the fault likely to lie with the clutch master cylinder?

[PaulC5]

The low temperature might be a reason for the stop/start to not be working, have a look in your hand book for the required conditions for it to work.

[RichardW]

I might have replied to this on FB.... but you didn't have the other code. Looks like it needs a new master cylinder (or there is a wiring fault). This was a common issue on earlier cars, but I haven't heard about it recently. My guess will be that if you fix this the SS will work and PB fault will go away. Can you see live data, what does it say about the clutch position?

[lambie413]

I might have replied to this on FB.... but you didn't have the other code. Looks like it needs a new master cylinder (or there is a wiring fault). This was a common issue on earlier cars, but I haven't heard about it recently. My guess will be that if you fix this the SS will work and PB fault will go away. Can you see live data, what does it say about the clutch position?

You did indeed! I did another scan and was able to get the code.

When you say clutch position do you mean the clutch pedal position on the live data?

I had a look at this last night. With the clutch fully out it was around 88%. With clutch pressed it went to around 12%.

Thanks for your help!

[RichardW]

Don't know what the figures are supposed to be, but that looks a bit suspect. Can you see freeze frame data when it set the code, what does it say?

[lambie413]

Here is the live data logged when the fault occurred on the Engine ECU:


and on the ESP ECU


Under the ESP ECU its says 'Invalid value' under the Position of Clutch Pedal.

Think there's a fair chance that it is the master cylinder. Given it's location and the amount of stripping required I think I might leave the job to my mechanic!