GS300newb

Hey everybody! I'm new here, new to Lexus ownership, and new to car maintenance. My partner was handed down a 2000 GS300 with 220k miles on it, and I've gotten a lot of great information here on how to get it back in fighting form. But this one problem has bedeviled me from the beginning and I'm at the frontier of my own resources.

I believe I have a parasitic battery drain. The car draws 90mA when it is off, and if the car sits idle for 5 days or more, the battery runs down. (I realize it's ideal to drive more than that, but we're in Brooklyn and we just don't need to drive every day.) I understand that 90mA is not totally crazy for more modern cars, but by pulling fuses with my multimeter connected to the battery, I've determined that the "DOME"/interior lights circuit is responsible for about 60mA of that draw.

According to the manual, the DOME circuit is responsible for the interior lights, personal (reading) lights, vanity lights, trunk light, and clock. I've confirmed that all of the interior lights, glove box light, and trunk light shut off automatically when they're supposed to. I've disconnected, in turn, the clock and the glove box light, and the draw happens regardless.

Any ideas how to home in on the problem? I talked to two local mechanics about the issue and it's clear they have no idea how to pin it down. Do I need to suck it up and go into the dealership?

UPDATE: I found the drain! After disconnecting literally every other component on the circuit, I realized that the stereo head unit was also connected to this fuse. Disconnected it and, sure enough, the stereo had been drawing those extra 60mA. As I understand it, it should be topping out at about 30mA, so it looks like I will be replacing it.

Mike246

If you have a 90mA draw, that's equivalent to 2 amp-hours over a 24 hour period. The battery (in mine, anyway) is 70 amp-hours. If your battery is flat after 5 days when you have taken 10 amp-hours it's time for a new battery.

I have not checked my quiescent draw but maybe 90mA is about right given that the clock, transponder receiver and security system are active. Have you overlooked the two small lamps on the underside of the dash when doing your measurement?

GS300newb

Thanks a lot for the reply. That math is really helpful. When this first started happening over this last winter, the first thing I did was replace the battery. Since it started happening again very soon after, I figured the problem must be elsewhere. But maybe I got a dud? My mechanic chose the battery (I only started tinkering in the last couple months) and it's entirely possible he gave me something cheap.

The security system and transponder receiver are on different circuits, according to the manual. Is it possible that they're still registering as part of the 60mA decrease when I pull the interior light fuse?

No, I didn't overlook them. The foot lights turn off automatically at the same time as the dome light. Thanks again for your help!

GS300newb

Update: I've also disconnected the keyless entry receiver and the CD changer, both of which are connected to the "DOME" circuit, and neither affected the draw. Would love any other ideas.