I have a '97 Maxima SE that appears to have a parasitic battery drain
problem. My wife drives the car short distances, leaves it for several
hours, then the engine won't turn over when she tries to start it. I
replaced the battery; it worked for a few days before the problem
The battery does appear to be getting charged by the alternator.
Measuring AC volts from the alternator, I get about 330 mV of ripple
output; I've heard that this should be less than 500 mV, so this
reading seems fine. Measuring voltage from the battery while the
engine is running, I get about 14V. After shutting off the engine the
battery at first reads about 12.5V, then drops slowly, by about 10 mV
every 15 seconds or so. About 8 hours after making the 12.5V
measurement, the battery reads about 12.1V. If it drops to 11.98V the
car won't start.
An ammeter connected in serial with the negative ground cable shows a
fluctuating 85-95 mA current with the vehicle shut down, doors closed,
etc. I pulled each fuse while checking this leak in order to determine
what might be causing it. Removing the BCU fuse drops the leak to
about 10 mA. The interior lights and trunk light only add to the
baseline drain. When the BCU fuse is left in place, the only fuse from
the interior that affects the reading is "Room.L" which drops it to
about 75-85 mA. There's also a fuse in the engine compartment, "FL.30A
Power Window" that drops it by about 3 mA. Other than that, no other
fuses appear to affect the baseline leak.
Is there anything I can do to further diagnose the BCU current drain?
Is this amount of drain normal? I've heard that most modern cars
shouldn't draw more than 30-50 mA at rest. The car is completely stock
with no added electronic components, no phone charger, etc. Are there
any components connected to the BCU that I can test? Pulling all the
fuses I could find with the BCU fuse in place didn't seem to change
anything much; is there anything else I can disconnect?
I know that a faulty alternator diode can cause battery drain, but
because most of the drain stops after the BCU fuse is removed, I don't
think the alternator is the source. Is it worthwhile having the dealer
check the alternator? There is a recall for the alternator on this MY,
but I don't think my VIN corresponds to the recalled vehicles.
Any comments or suggestions would be appreciated -- thanks!