Starting and Charging: Testing and Inspection

Perform Troubleshooting In The Case Of Overvoltage

This document provides the necessary information and instructions for troubleshooting on vehicles where overvoltage has occurred.
In the vehicle electrical system, the control units are configured in such a way that they should withstand short voltage peaks above the maximum supply voltage of 16 V without functional limitation. However, if voltage peaks while the vehicle is being driven exceed times of more than 300 ms, typically the following possible sporadic symptoms can be observed by the customer:
- the on-board computer goes dark.
- the interior lighting becomes brighter or flickers.
- failure of the ASC/DSC system and ASC+T/DSC indicator and warning light lights up in the instrument panel.
- failure of the steering column switch cluster: problems with windscreen wipers, turn indicators, etc.

The possible causes for sporadic occurrences of overvoltage are:
- a load shedding on load-current consumer units or high-current consumer units due to loose contacts.
- a faulty alternator.

Procedure
- Allow read out of all fault memory with a vehicle test and display additional information such as kilometer reading and voltage values of all stored fault entries "overvoltage".
- Check battery contact at the positive and negative terminals: Are the connection terminals tight enough?
- Check earth points and earth connections.
- Check plug connections and contacts of the high-current consumer units of the vehicle:
- Electric auxiliary heater based on PTC principle, if installed.
- Combustion preheating control unit (diesel-engine car).
- electric fan.
- other high-current consumer units that might be installed in the vehicle.
- Check the alternator using the alternator diagnosis: function, plug connections and contacts, BSD line, etc.
- Try to find out whether the vehicle wasn't jump-started or charged by a 24-volt battery (e.g. lorry).