Trailer Hitch Retrofit

A trailer hitch retrofit is not just a mechanical job, a variety of control units need to be adjusted to make the vehicle safe.

Gateway

Control unit 19 (Gateway)
Installation list
69 Trailer Control → Coded ✓

With OBDeleven you hit the plus button (+) in the bottom right of the Control unit overview and set a tick on 69 Trailer Control.

Engine – 01

Control unit 01 (Engine/Motorelektronik)
Coding (07)
(Trailer installed/Anhänger verbaut)
Byte 05, Bit 4 → Activate ✓
or
Byte 06, Bit 4 → Activate ✓

Brakes – 03

Control unit 03 (Brakes/Bremsenelektronik)
Security access (16): 61378 or 24990
Adaptation (10)
Trailer Recognition and Stabilization/Gespannstabilisierung → Activated ✓

With the Bosch ESP8 front-wheel drive, a coding is performed instead of adaptation.

Control unit 03 (Brakes/Bremsenelektronik)
Security access (16): 61378
Coding (07)
(Trailer Recognition and Stabilization/Anhänger - Erkennung & Stabilisierung)
Byte 01, Bit 7 → Activate ✓
or
Byte 02, Bit 6 → Activate ✓

Central electrics – 09

Control unit 09 (Central Electrics/Zentralelektrik)
Security access (16): 31347
Coding (07)
(Trailer Hitch Controle Module - installed/Anhängeranschlussgerät - verbaut)
Byte 01, Bit 1 → Activate ✓
or
Byte 13, Bit 4 → Activate ✓
or
Byte 14, Bit 5 → Activate ✓

For 2017 and younger models, an adaptation must also be carried out.

Control unit 09 (Central Electrics/Zentralelektrik)
Security access (16): 31347
Adaptation (10)
Vernetzung
- Anhängeranschlussgerät → Activated ✓

Parking sensors – 10/76

Control unit 10 or 76 (Parking Assistance/Einparkhilfe)
Security access (16): 71679
Coding (07)
Byte 03, Bit 0 (Manually removable/Manuell abnehmbar) → Activate ✓
or
Byte 03, Bit 1 (Pivoting/Elektrisch betätigt) → Activate ✓
or
For a 3-byte long coding:
Byte 00, Bit 0-1 (Trailer hitch - installed/Anhänger - verbaut) → Activate ✓

Exception for Audi A4 8K: Not possible from MY 2014, because the parking assist is integrated in the Central Electrics (09).

Adaptive cruise control – 13

Control unit 13 (Adaptive Cruise Control/Distanzregelung)
Security access (16): 20103 or 14117
Coding (07)
(Control module for trailer recognition/Steuergerät für Anhängererkennung)
For a 7-byte long coding:
Byte 02, Bit 3 → Activate ✓
or
For a 12/15/23-byte long coding:
Byte 03, Bit 3 → Activate ✓
or
For a 3-byte long coding:
XXXX8 → XXXX1 (53168 → 53161)
1 - with Trailer | 8 - without Trailer

Dashboard – 17

Control unit 17 (Dashboard/Schalttafeleinsatz)
Coding (07)
(Trailer assistant)
Byte 12, Bit 5 → Activate ✓
or
Byte 14, Bit 5 → Activate ✓

Comfort system – 46

Control unit 46 (Comfort System/Komfortsystem)
Coding (07)
(Trailer monitoring/Trailer control unit)
Byte 04, Bit 7 → Activate ✓
or
Byte 12, Bit 5 → Activate ✓
or
Byte 18, Bit 5 → Activate ✓

Infotainment – 5F

Control unit 5F (Multimedia/Informationselek. I)
Adaptation (10)
Car_Function_Adaptations_Gen2
- menu_display_trailer_assistant_after_disclaimer → Activated ✓
- menu_display_trailer_assistant_over_threshold_high → Activated ✓
Car_Function_List_BAP_Gen2
- Trailer_Assistant_0x36 → Activated ✓
- Trailer_Assistant_msg_bus_0x36 → Klemme 15

Chassis control – 74

Control unit 74 (Chassis Control/Fahrwerkssteuerung)
Adaptation (10)
Trailer/Anhänger → Activated ✓

Driver assistance – A5

Control unit A5 (Driver Assistance/Frontsensorik)
Coding (07)
(AAG/FW_AAG/Trailer recognition/Anhängererkennung)
Byte 16, Bit 1 → Activate ✓
or
Byte 14, Bit 1 → Activate ✓
or
Byte 11, Bit 0 → Activate ✓

Lane-Assist – 3C

Control unit 3C (Lane-Assist/Spurwechselassistent)
Coding (07)
(ECU for draw bar)
Byte 00, Bit 4 → Activate ✓
or
Byte 02, Bit 6 → Activate ✓

Rearview camera – 6C

Control unit 3C (Rear View Camera/Rückfahrkamerasystem)
Coding (07)
(Equipment AHK/equipment_ahk)
Byte 04, Bit 0 → Activate ✓

Trunk lid – 6D

Control unit 6D (Deck Lid Control/Heckdeckelelektronik)
Coding (07)
(Trailer/Anhänger)
Byte 01, Bit 7 → Activate ✓
or
Byte 04, Bit 0 → Activate ✓

Small note: If the car already has module 69 (Trailer Control), which is possible for cars with trailer preparation, it is necessary to enter that module and check if the connection diagnostics is active. Usually it’s in Byte 01.