Retractable Towbar. Part 2 ― Connection and Coding

Electric diagrams

I had to use German ELSA, as it was the only source to find diagrams of 2017+ cars.

SD fusebox placement


As I mentioned in the previous post, I decided not to add additional fusebox (SD) but to insert the fuses in the main one: SC27, SC28, SC38, and SC44 slots were available.

Matte fuses from the Skoda kit look different

I disassembled the left side of the trunk, removed plastic from the steps, and lay down new wirings for the towbar and PLA3 sensors (more on this in the next post).

Skoda uses different points to connect to the network (easier to reach!), but in general, everything is identical to Volkswagen and Audi cars – 4 wires to plug in the units:

  • CAN-Comfort bus (5 / 15 pins in the Gateway, or A16 / A17 pins of the BCM)
  • A14 pin of the BCM
  • Stop signal indicator (Skoda diagram: BCM C58 pin. Audi uses the red square connector near the footrest, T17c/7)

Towbar wiring goes out of the cabin from the second technical hole in the left side of the trunk. It is covered by the rubber cap and a wax. The control unit should be snapped inside the plastic housing 8V0 907 333, but it didn’t arrive in time and you see zip-ties mount in the photo below.

Skoda wiring kit has 4.8mm mass wire splitted into 3 contacts in a big connector, Audi gets it with only one 2.5mm wire. I cutted out Skoda solution and replaced it to the original 191 972 711 connector.

I’ve cut the plastic and added button to the center of the left niche:

The button of the Audi does have an icon backlight and this is why the 5th wire is needed. This distinguishes the “premium” brand from Skoda and others. I decided not to worry about the icon and didn’t connect it, since the backlight is white – like any other facelift car.


The central section of the diffuser requires some remodeling: the original opening is only on the left, but the hook swings from the right – I had to cut out everything from the other side too. I did so in two steps:

The first (green) piece was not enough


Gateway 19 — add Trailer 69 to the list of installed devices.

Engine 01 enable:
Byte 5 Bit 4: Trailer installed

ABS 03 enable in adaptations:
IDE04774-Vehicle and Trailer Stabilization: activated

BCM 09 enable:
Byte 1 Bit 1: Trailer Hitch Control Module installed

Park Assist (PLA) 10 enable:
Byte 3 Bit 0-1: 02 Trailer Hitch installed (electrically operated)

АСС 13 enable:
Byte 2 Bit 3: Trailer Recognition Control Module installed

Side Assist 3C enable:
Byte 2 Bit 4-7: 20 Trailer Recognition Control Module installed

Rear view camera 6С enable:
Byte 4 Bit 0: Trailer Recognition Control Module installed

ALA А5 enable:
Byte 16 Bit 1: Trailer Recognition Control Module installed

Trailer 69 enable:
Byte 4 Bit 0-7: 02 Terminal 30 Output switched (Pin 10) active while Trailer connected

After all the coding is done, the car should disable rear parking sensors and Side Assist when the trailer is connected. The rear view camera switches to the 3rd mode with a center line to make docking easier. ABS is also additionally involved in trailer stabilization while driving.

In use

I installed towbar mostly because of the bike rack. I became very interested in this type of mounts after this Audi commercial. Roof racks are much harder to use, and more likely to scratch everything around. My personal fear is bikes swaying in the wind.

4H0 071 105 – original Audi rack for two bicycles from this advertising

The load on the ball from above should not exceed 75kg because of the swivel mechanism; static options usually have 100-120kg. According to the manual, the car can drag a regular trailer weighing 750kg, and up to 2000kg for the trailers equipped with their own brakes.

Until the hook is locked in one of the positions, the red indicator on the button is flashing. But the light is always red in a locked state, so it’s not clear why the icon even needs a backlight. I saw that indicator changing colors in other cars, but this is not the Audi case.

The towbar is equipped with a modern 13-pin socket, but many trailers still use the old one – I bought 13 → 7 adapter.

Diffuser cover locks in with two knobs


Next →  
Park Assist PLA 3.0
  ← Previous
Retractable Towbar. Part 1 ― Parts and Wires


temp temp

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