Mercedes-Benz W204 turn signal fault messages
Mercedes-Benz W204: the instrument cluster reports a turn signal fault or the signal ticks fast even though the turn signals work. What is the cause?
The cause varies, but often the fault is poor contact in the lamp connector or in the tail light ground wire, which can corrode or come loose from the connector. The connectors can be cleaned and the wires repaired. There is no separate turn signal relay; the turn signals are controlled by transistors.
Mercedes-Benz W204: how is a bad ground told apart from other faults?
Switch on the tail lights and the brake at the same time as the turn signal. If both affect the turn signal, the shared ground wire is in poor condition. The lowest wire, usually brown, is the ground and fails most often. An extra ground does not always help.
Mercedes-Benz W204: can an LED tail light cause a turn signal fault?
Yes. If LED parts of the tail light are broken, the turn signal can light dimly, drop out or the car can use the brake light as the turn signal. Replacing the LED light's wiring harness or the bulb holders does not necessarily help; the fault was fixed by replacing the whole tail light.
Mercedes-Benz W204: what if the turn signal also blinks on the other side when turning while cold?
The fault is usually in the multifunction switch, that is, the steering column stalk unit, and it is not repaired without replacing the switch. Replacement is easy, but the new switch must be set in exactly the right position so that the position sensor does not get confused.