This guide provides instructions on how to replace the auxiliary battery relay (K57/2) on Mercedes-Benz vehicles.
The Mercedes auxiliary battery relay is typically mounted at the top of the firewall, right below the windshield wiper motor.
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If you have replaced the auxiliary battery and are still getting the message, "Auxilary battery malfunction," there is a chance that the auxiliary relay may be the culprit. See our video where we explain the Mercedes-Benz auxiliary battery problem.
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