Mercedes SL500

Into our workshop was this Merc that had problems with the aux battery under the bonnet not charging. This battery is used when cranking to help give extra amps. Also it is isolated from the main battery when ignition is off, so if main battery goes flat the vehicle can use this battery to in essence jump start the car.

The battery symbol was lit on the lcd panel on dash and the aux battery had gone flat.

There is a split charge relay that controls this along with a battery stabilisation module. We gained access to these components (not easy being a cabriolet, having to remove part of the roof mechanism) and checked wiring associated with this system all checked ok. On gaining access to components a burning smell was noticed but no burnt wiring was seen. With the battery disconnected the relay and module were removed and checked

The battery stabilisation module was burnt. We replaced this with a new O. E part and replaced charge relay to be safe reset fault codes and checked. Job correct first time and no unnecessary parts fitted.


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