DS3 electrical problem

[KamenovKamen]

Hi guys, new to the forum.
I need some help please.
Ds3 2012 1.6 e-hdi 90 hp
Does someone know what is this cable for ?(pictures attached)
Long story short- the car has an “engine fault “ showing on the small radio display- no engine management light on the dash.
ECO mode deactivating as soon as I start the engine and won’t go active no matter what.
On the next morning the car couldn’t start cos the battery was flat and I found a parasitic draw from the cable on the pictures. I found out the alternator won’t charge the battery then I’ve changed alternator + battery( battery was dead- probably shorted) - the car now starts and runs normal but “engine fault” on display still there and ECO mode won’t activate same as before.
This cable needs to stay disconnected otherwise it drains the battery overnight.
The cable goes to F3- 40A fuse on top of the battery.
I suspect short with whatever is on this cable, but can’t find where is the cable going to. Diagnostic not really helpful. Showing BSI sometimes but it clears and stays clear and the faults are still there.
Any idea?

Thanks in advance!

[GiveMeABreak]

The BCP3 (Relay 3 protection switch unit) has three fuses, F1, F2 & F3. All these Fuses are 40A and are for the heater protection - Air Conditioning.

[KamenovKamen]

The BCP3 (Relay 3 protection switch unit) has three fuses, F1, F2 & F3. All these Fuses are 40A and are for the heater protection - Air Conditioning.

Hi, thanks for the fast reply!
I don’t have 3x40A there. Only 1x40A, then 30A,70A and 2x80A as shown on picture.
Or maybe I didn’t understand what you mean?
Thank you !
EDIT: these are the fuses on top of the battery.
Picture for location attached.
I guess you already know that but worth mentioning.
The fuses there are F7,F3,F6,F4,F8(unused) and F5 in the same order left to right.

[GiveMeABreak]

No, that's not the same place. What you are showing are the main Maxi Fuses, which is not the same as the BCP3 unit.

If you have your VIN, (please post your VIN in full without spaces - it will be automatically masked from public view after submitting your post & will only be visible to staff), I will be able to look at the specific diagram for your vehicle, but the BCP3 unit is separate to the maxi fuses:

[KamenovKamen]

The VIN number is: VF7**************[VIN obfuscated, can be read by forum staff]
Thank you

[GiveMeABreak]

Here's the Fuses:



PSF1: Engine compartment fusebox panel
1021: Reversible alternator
BFDB: Fuse box at the battery outlet
BCP3: Relay 3 protection switch unit
1031: Battery charge status unit
1012: Centralised voltage maintaining system

Here is the BFDB (Fuse Box at Battery Outlet):

[KamenovKamen]

Thanks a bunch! You guys are amazing!

[KamenovKamen]

I’ve read the car again today with different diagnostic tool. I get code U1134. What could that be ?

[GiveMeABreak]

Here you go:

Fault Code:	U1134
Description of Fault:	LIN: Voltage retention device confirmed absent. Faults in communication between ECUs on the LIN.
Conditions for Fault to clear:	Ignition switched on
Downgrade Modes whilst Fault is active:	Automatic restarting impossible following stopping of the engine (Requires restarting of the engine using the key).
Symptoms:	Problem with automatic restarting of the internal combustion engine Absence of automatic stopping of the internal combustion engine Malfunction of the Stop and Start switch or its LED
Suspect Areas:	Supply of the voltage retention device Reversible alternator supply Electrical harness