Mercedes SL 550 Battery Light on After Starter Replaced
Vehicle: 2011 Mercedes-Benz SL 550 (230.471), V8-5.5L (273.965), Automatic Transmission/Transaxle
Mileage: 39,453 miles
Problem: After the technician installed a new OEM starter motor, the battery light came on. There were no diagnostic trouble codes (DTCs).
Case Details: After installing the new starter, the technician reconnected the batteries. As soon as he started the engine, the battery light appeared. He load-tested both batteries. The main battery failed, so he installed a new one, but the battery light remained on.
A quick call to ALLDATA Tech-Assist shed some light on the problem. The batteries were disconnected/reconnected in the wrong sequence. When disconnecting the batteries, you need to disconnect the main battery first, then the starter battery. If you don’t follow this sequence, then you need to disconnect the starter battery first, then the main battery, wait 20 minutes, then reconnect the starter battery and finally the main battery. NOTE: The SL550 has two batteries: a main battery under the hood (for starting) and an auxiliary battery in the trunk (for electronics).
Confirmed Repair: After following the battery disconnection/reconnection sequence correctly, the battery light did not reappear. Easy fix!
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