BMW 12317508054 Exchange Alternator, Water-Cooled

Do not disconnect the battery while the engine is running, as this may cause damage to the alternator or engine electronic systems. Only use a digital multimeter when testing charging system components. With the ignition ON, check that the battery warning light illuminates. If the warning light does not come ON, repair any bulb or wiring faults before proceeding with the charging system check. To check for battery voltage at alternator terminal 30 (B+), pull back the rubber insulating cover at terminal 30 at the rear of the alternator, then connect a voltmeter between terminal 30 and ground to check for battery voltage; if voltage is absent, inspect the wiring for faults. Battery voltage can also be verified between the B+ terminal on the left cylinder head and ground. Disconnect the harness connector from the alternator, turn the ignition ON, and check for battery voltage between terminal 15 and ground; if voltage is not present, examine the wiring and fuses for faults. Reconnect the connector to the alternator and locate the blue wire from terminal 61E of the alternator connector, carefully connecting the positive test lead to the wire using a piercing test lead end. With the ignition ON, check for voltage, which should be less than 1.5 v, and the charge indicator lamp should light. After ensuring all test equipment and tools are clear, start the engine; voltage should increase to 8.0 v or higher, and the charge indicator light should go out. If voltage does not increase and the system is not charging, the fault lies within the alternator. If voltage does not increase but the system is charging, interrogate the system for faults using an appropriate BMW scan tool and reset the fault memory. If a load tester is unavailable, a quick alternator output test can be performed by running the engine at about 2000 rpm and turning on electrical loads such as fans, lights, rear window defroster, and wipers; with all accessories on, battery voltage should remain above 12.6 v.

The water-cooled alternator is an enclosed unit mounted on the engine-block, within the circuit of the water jacket and is, therefore, an engine-cooled unit. For these reasons, it is a 'brushless' sealed unit and cannot be serviced: the temperatures need to be kept constant to prolong the life of the unit. It also has the welcome side-effect of removing the alternator cooling fan, which results in even less noise. Also incorporated in this alternator is the load start reduction which reduces the time to start an engine particularly in cold climate because during starting the current load is limited to only 20 amps to minimize the alternator braking torque on the engine and as the starter engages full output is progressively developed.