C4 Grand Picasso B78 2015 lock wiring fault INFO

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C4 Grand Picasso B78 2015 lock wiring fault INFO

Post by citroenguy »


Just wanted to share my experince with my father's car, someone might find it useful..

He's had an issue where the drivers door (LHD car) wouldn't lock unless you locked it mechanically. And subsequently would unlock all doors when pulling the handle of the drivers door.

He had already tried a new lock actuator, so, since it has 278000km's we wanted to check the "bendy wires" in the door jamb. Common issue on older cars.

So i dissassembled the door and found a corroded off thin green cable (ground?) (probably pin hole in manufacturing of 1000's of meter of wires), but no other cracked insulation och broken off wires.
Fixed the that wire, but the symptom persists..

Now i muttered some well chosen words :evil: and broke out the multimeter and bought 1 hr of servicebox time to get wiring diagrams.

So, after "mesauring" signals backprobed on lock or unlock and main ground in the connector. OK, so we have unlock signal but no lock signal from BSI (no door ECU) nowhere in the door.
So next i check on the car side in the A-post, nothing... Um hmm, so check at the BSI conncector -not possible. So i removed the BSI (a bit of a faff) and ohm-checked the circuit, Bingo! 7.1 Ohms in the lock circuit. I don't even need to load check that, which would hav been annoying since im only working out of my tools in the boot..

Might be a "hack" solution but i spliced in an extra wire from the lock circuit. But about here i saw that the boot shares the lock circuit with the drivers door, bugger!
So now there is still 7 Ohms to the boot (still connected to original wire), but the drivers door locks with the fob! But the boot never locks, not 100% if it locked before.

Ah well now we know what the fault is..
I have various repair handbooks and wiring diagrams for C5 mk1, Xantia, XM, Berlingo and C3 mk1.
I have Lexia/Diagbox (Sweden) and Servicebox/sedre