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dinkin ... 1/19/2013

2002 Lexus IS300 Base 6 Cyl 3.0L


My car will not hold a charge even after jumping it off. I bought a new battery several months ago, and now its dead.

How to tell if it has an altenator problem before taking it to Lexus to run a diagnostic?

2 Answers


Bill 1/19/2013

If battery new and all battery clamps are clean and tight, I would be about 99% sure it to be the alternator. It could be the voltage regulator but that is built into the alternator so, still alternator. If you have a voltmeter you can check by with engine running and voltmeter set to DC volts and probes across battery terminals , voltage should read 13.5-14.5 Volts DC, if below this then alternator bad. Hope this helps.


t.juncewicz 2/5/2013

If the alternator is putting out correct voltage then you need to determine what is discharging the battery and how long it takes between driving.
measure the voltage after driving the car (nice drive) 12.xx volts then measure the voltage the next day before driving
if its lower then 12.xx then you are drawing excesive current when its parked
then you need to determine how much its drawing
there some active components when the car is parked but there is a limit
extra draw will discharge the battery over a period of time
then you need which component is doing that


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