Volkswagen Golf Quiz
Guide for using trailers

Trailer detector control unit -J345-

In this manual: Guide for using trailers
General body repairs, exterior — 230General body repairs, interior — 279General information, paint — 133Vechile- specific paint information — 27Heating, air conditioning — 156Auxiliary heater — 58Air conditioning system with refrigerant R134a — 1297- speed dual clutch gearbox 0CW — 544- cylinder injection engine(1.4 1 direct inction. turbocharger) — 182Fuel supply system - Petrol engines — 59Running gear, axles, steering — 221Brake system — 92Wheels and Tyres guide — 12Guide for using trailers — 11Wheels and Tyres Guide - General Information — 121Brake system (hybrid) — 73Electrical system — 326Communication — 65Electrical system, general information — 111
~1min read

General description:

The trailer detector control unit -J345- detects a power consumption of at least 5 W → Remark when “towing a trailer” and passes this information to various control units via the CAN data bus. The trailer detector control unit -J345- receives information (regulation of lights) from the onboard supply control unit -J519- and the convenience system central control unit -J393- via the CAN data bus.
  1. The turn signal system or the side lights must be switched on to detect the “trailer”.
Information concerning checking the control unit, fault displays and fault finding is located in the workshop manual → Electrical system; Rep. gr.97.

Retrofitting trailer detector control unit -J345-

Retrofitting a trailer detector control unit -J345- is possible in essence but not easy because it has to be connected to the CAN data bus of the vehicle. The control unit then has to be coded with the aid of “Guided fault finding” → Vehicle diagnostic tester. Note It is recommended that alternative control units available on the open market and not approved by Volkswagen are avoided without exception. If equipment of this type is installed, the guarantee will become void. Generally, these are connected to the tail lights and not integrated in the electrical system of the vehicle, which makes far more sense. The consequence is that faulty diagnoses in the bulb failure warning system or malfunctions can occur, among other things. Furthermore, dimmed bulbs (combined brake and tail light) cannot be actuated.

Coding trailer detector control unit -J345-

Coding is described in → Electrical system; Rep. gr.97.

Test yourself

A quick Volkswagen Golf quiz: every answer comes with an explanation and a link to the manual page.