When servicing vehicles with a 48V system, you should pay special attention to occupational safety. Additional electrical licences are not required to operate this type of system, but you should follow appropriate safety procedures to eliminate the risk of accidents. On select vehicle brands, it is a basic safety procedure to deactivate the 48V system before performing specific operations. The deactivation procedure is required, among others, when replacing auxiliary system components. To carry out the disconnection procedure, use a suitable diagnostic device with this function. You should follow additional maintenance procedures for vehicles with a damaged system or 48V battery, such as in an accident.Service challenges in 48V systems that can occur in accident vehicles relate not only to mechanical damage, but also to blocking of the 48V system for safety reasons. As an example, we will use a Volvo vehicle, the 2021 model XC 60, with a 2.0-litre diesel engine delivering 145 kW. In this vehicle, when an event impulse is detected by the airbag controller, the system operation algorithm may decide to disconnect the auxiliary battery from the 48V system. The algorithm makes this decision regardless of whether the pyrotechnic elements for the protection of the driver and passengers, i.e. seat belts or airbags, have been activated. After disconnecting the auxiliary system as a result of detecting, for example, a collision, an appropriate error code is saved in the memory of the controller that supports the 48V system battery. Example below:
5. Memory error
B16527F Crash detected
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Component disconnected
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Fig. 2 Error code of high-voltage disconnection as a result of a collision read in the 48V system battery controller [BOSCH KTS diagnostic tool]
The disconnection of the system is carried out by the disconnecting relay, which is located inside the auxiliary battery, and its status can be verified by analysing the actual parameters of the controller. Reactivation of the relay is impossible while the error code B16527F is stored in the controller’s memory. Usually, it is impossible to remove the defect in question; when it is registered, in accordance with the manufacturer’s recommendation, you should replace the 48V system battery controller. On this particular vehicle, the battery controller is located inside the auxiliary battery and is replaceable with the entire battery.
48V Battery, Disconnect Relay: switch status
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Status: component open
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Fig. 3 Status of the 48V system disconnecting relay read out in the battery controller [BOSCH KTS diagnostic tool]