Technical Park assist wiring loom puzzle

[siwalker]

Hi,
Can anyone shed any light on this? This is the wiring loom running from the factory-fit sensors in the rear bumper up to the control unit in the rear light cluster. Tucked away in the corner of the bumper is this main connector plus a 2-pin connector with nothing connected to it. I have a sneaking suspicion this is a connector for parking sensor deactivation. The control unit apparently has a connector pin that if tied to chassis earth will deactivate the sensors. The wires into this unused connector are black and red/white.
I'm trying to find a solution to the problem of the sensors not being deactivated when there's something attached to the towbar. The towbar was recently installed by Towsure, who claim there is no solution to this, despite supplying a 'vehicle-specific wiring kit' at astronomical expense. The FIAT manual asserts that the parking sensors are deactivated when towing - presumably if a FIAT towbar is installed, but the capability is there.
The towbar is primarily used for a bike rack and this is a van conversion motorhome (Carthago Malibu), so reversing is not infrequent.

I can unplug this loom and the sensors stop working, with a dashboard reminder that they're off, but it would be nice if I could fit a switch to do it.

Supplementary question - can anyone identify the connector type here?

Thanks,
Simon

 

[Anthony489]

Hi siwalker

I can only give you extracts from elearn for the X250 (2006 to 2014), so if your van is newer then they are only a rough guide to the Fiat way of doing things. They were prone to change things (especially wire colours) so no guarantees !

For this era of van, Pin 6 of 8 Pin Connector B of the Reversing Sensor Control Unit M084 is used optionally to deactivate when a trailer is fitted. If you are lucky, this is now wired out to your unused 2 pin connector with a white/red wire along with a ground (black) wire. I would expect the towbar fitting harness to link these to the 13 pin trailer socket to exploit its inbuilt "trailer plugged in" function, see 13 pin trailer numbering picture.

The same connector B is populated with 6 pins (Nos 1,2,3,4,5,8) for the wiring to the sensors. The colour codes are:

BZ White/Violet
NZ Black/Violet
HR Grey/Red
BN White/Black
BV White/Green
BM White/Brown

The other connector on the control unit is 12 Pin Connector A, which is populated with pins 1,6,7 and 12, and is used for power, ground and Bus connections.

More information about trailer connectors and trailer sensing here: https://caravanchronicles.com/guides/iso-11446-13-pin-trailer-connections/

Good luck

 

[Anthony489]

Hi again

Just to add another thought. If your vehicle is new-ish it might use the Canbus system to detect the presence of a trailer, by sensing the loading of the various light bulbs on the 13 pin socket. If your trailer board uses LEDs, its just possible that they don't present enough loading for the system to recognise. If so, a quick check with a borrowed "old fashioned" trailer board with conventional bulbs might tell you one way or another.

Even MOT testers have been led a merry dance by "approved" trailer test sets using LEDs that give odd results with some vehicles.

 

[siwalker]

Hi again

Just to add another thought. If your vehicle is new-ish it might use the Canbus system to detect the presence of a trailer, by sensing the loading of the various light bulbs on the 13 pin socket. If your trailer board uses LEDs, its just possible that they don't present enough loading for the system to recognise. If so, a quick check with a borrowed "old fashioned" trailer board with conventional bulbs might tell you one way or another.

Even MOT testers have been led a merry dance by "approved" trailer test sets using LEDs that give odd results with some vehicles.

Hi Anthony,
Many thanks for this and your earlier reply. I should have said the van is a 2018 X290 Ducato. The bike rack in question has LED lights. I'll see if I can find a filament bulb board to borrow for further testing.
It seems likely on the face of it that closing the connection between those two pins on that trailing socket would give the parking sensor ECU the message that a trailer is connected. Unfortunately the conversion is such that the ECU is inaccessible to check where that red/white connector goes to on the ECU. I think the ECU might be accessed once the rear light cluster is dropped out but even that is nigh-on impossible due to the tiny access panel provided by the converter and the water filler pipe occupying most of the space. I can release the upper retaining nut but the lower one would require smaller hands than mine. I need to see if I can remove some internal trim panels to get proper access. Whoever makes it so hard to get to light units should be shot.
Does anyone know what that connector type is on the 2-pin trailing socket? I must have looked at 5000 images of automotive connectors yesterday and can see nothing like it!
Simon