The brief
Mr An's C180 wouldn't start and he was referred to us. A no-start has a few causes, but when a check finds the drive belt has given up, the chain becomes clear: the belt drives the alternator, and once the belt's gone the alternator stops charging, so the battery quietly runs flat until the car won't crank. The drive belt at the front of the engine runs the alternator, the power steering and the air conditioning compressor off the crankshaft, over a tensioner and idler pulleys. Over the miles the belt hardens, cracks and glazes so it slips, and the tensioner loses its spring and the idler bearings get rough. A slipping or snapped belt kills the charging, and a proper job does the belt plus the tensioner and the idlers as a set, with the battery checked and brought back to charge.
The diagnosis
A check found the drive belt past it, glazed and cracked and no longer driving the alternator properly, and the battery flat as a result, not a fault in the battery itself. The tensioner had lost some of its spring and the idler bearing was rough too. So it was a full drive belt set plus a battery recovery: the belt, the tensioner and the idlers together, and the battery recharged and load-tested to confirm it was sound.
The work
The old drive belt was removed, then the tensioner and idler pulleys, and a new genuine Mercedes-spec belt fitted along with a new tensioner and idlers, the routing checked against the diagram and the belt seated properly. With the belt back driving the alternator, the battery was given a proper charge and load-tested, and the charging voltage checked across idle and load to confirm it was holding. A road test confirmed a strong crank, steady charging voltage, no belt noise, and everything the belt drives working as it should.
The outcome
A strong start, steady charging, the belt running quiet and true, and the no-start sorted at its source. The C180 went home starting properly again. A worn drive belt that gives up kills the charging and flattens the battery, so renewing the set and bringing the battery back fixed the cause, not just the symptom, the kind of repair that beats a quick jump-start that leaves you stuck again.
