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My wife's 2001 ES300 has had a slow battery drain that results in a low battery charge and inability for the car to start after several days of not being driven.  I first charged the battery to 12.7 volts with a battery charger, I checked the alternator and found charging at 14. 4 volts and took the battery to Pep Boys to conduct a load test and battery condition after 1.5 hour charge.  Battery checked out in good condition.  I then proceeded to finding what was causing the battery drain.   Using a multimeter set on "amps" I removed the ground connector from the battery and hooked one multimeter lead to the battery and the other lead to the disconnected battery ground cable connector.  After 3-5 min. with the ground strap disconnected, I took a reading of the battery drain.  The multimeter showed a 150 ma current drain.  At that point I started pulling fuses to see which would stop the drain.  When I pulled the 10a ECU-B fuse the drain immediately dropped to 20ma.  The question I have is what devices/circuits receive power through the ECU-B fuse?  Second, what further steps can I take to determine what device/circuit fed from this fuse are drawing current with the key off and the car sitting idle? 

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At this stage you need a wiring diagram, something that Lexus does not pass around cheaply. You might try finding a Camry V6 wiring diagram (possibly easier to locate) or go online to a site that allows downloads of sections of Lexus f-Factory Service Manuals for a fee. Here's a link to a site that may have what you need for a $7.50 one month charge:

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