Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Trailer Recognition Control Unit, Basic Function - GF31.19-P-9890A
Model All (4xWD)
with code E43 (Socket, 13-pin, 12 V, external at rear)
Model All (CAR)
with code 550 (Trailer coupling)
Overview
This document contains information on:
- General
- Function
General
The trailer recognition control unit is located on the right in the trunk/load compartment.
Function
The trailer recognition control unit is connected to the network architecture of the vehicle.
The trailer recognition control unit controls the lighting system of the trailer and the swiveling of the ball neck (vehicles with electrically-driven ball neck). To implement the functions, the trailer recognition control unit processes, among others, the following information:
- Circuit status
- "Switch on light function on trailer" request
- Request for trailer socket emergency shutoff
- "Swivel ball neck" request (vehicles with electrically driven ball neck)
- Trailer tightening angle request (vehicles with trailer maneuvering stabilization)
The trailer recognition control unit processes these input factors and sends, among others, the following information:
- "Trailer detected" status
- Status of light functions on trailer
- Position of ball neck
- Status of ball neck lock (vehicles with electrically-driven ball neck)
- Trailer rotation angle (vehicles with trailer maneuvering stabilization and articulation angle sensor)
- Show display messages request
| Component descriptions | |||
| Component description for trailer recognition control unit | Model 223 | GF31.19-P-4050A | |
| Model 243 | GF31.19-P-4050B | ||
| Model 206 | GF31.19-P-4050C | ||
| Model 297 | GF31.19-P-4050D | ||
| Model 295 | GF31.19-P-4050E | ||
| Model 296 | GF31.19-P-4050GG | ||
| Model 254 | GF31.19-P-4050H | ||
| Model 464 | GF31.19-P-4050J | ||
| Model 214 | GF31.19-P-4050K | ||
| Model 118 as of model year 2023 Model 177, 247 as of model year 2022 | GF31.19-P-4050L | ||
| Model 294 | GF31.19-P-4050N |
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.