BMW 5251 Service Manual page 380

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/Battery, Starter, Alternator
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Check for battery voltage at alternator terminal 30 (B+)
(ar-
row):
Pull back rubber insulating cover at terminal 30 at rear of
alternator.
Connect voltmeter between terminal 30 and ground and
check for battery voltage. If voltage is not present, check
wiring for faults.
NOTE-
On V-8 engines, access to the rear of the alternator is limited.
Check for battery voltage between the jump start post on the
left cylinder head and ground.
r Disconnect harness connector from alternator. Turn ianition
on and check for battery voltage between terminal l g a n d
ground. If voltage is not present, check wiring and fuses for
faults.
Reconnect connector to alternator.
Locate the blue wire coming from terminal 6 1 E of the alter-
nator connector. Carefully connect the positive (+) test lead
to the wire using a piercing test lead end.
Turn ignition key on and check for voltage. Voltage should be
less than 1.5 VDC and charge indicator lamp should light.
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Making sure all test equipment and tools are clear, start en-
gine. Voltage should increase to 8.0 VDC or higher. The
charge indicator light should go out.
If voltage does not increase and system is not charging,
the fault is in alternator.
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If voltage does not increase, but system is charging, inter-
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roaate svstem for faults usina an appropriate BMW scan
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tool and'reset fault memory.
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If a load tester is not available, a quick alternator output test
can be done by running engine at about 2000 rpm and turn-
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ing on electrical loads (fans, lights, rear window defroster,
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and wipers). With all accessories on, battery voltage should
be above 12.6 V.