LS - 1st and 2nd Gen (1990-2000) Discussion topics related to the 1990 - 2000 Lexus LS400

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Old 01-24-19, 08:52 PM
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Ryancucf20
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hello. I’m new here but have had my 99 ls400 for about 8 months. Recently I have had a problem with a voltage drop and parasitic drain that was found to be from the MPX-B fuse. What is the best way to go about finding my problem with this fuse. As I know it is conected to a lot of systems in the car. My driver rear window does not have the automatic function as it should. The pass window has a typical Toyota issue of rolling up some then going back down when using the auto up. any suggestions???
Old 01-24-19, 09:35 PM
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Yamae
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Before I write, I need to know the parasitic current level of the MPX-B fuse. Depending on the level, this is going to be a tough work to complete.
Old 01-24-19, 09:36 PM
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Ryancucf20
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The draw was 1.05 amps
Old 01-24-19, 10:35 PM
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Yamae
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Originally Posted by Ryancucf20
The draw was 1.05 amps
Sounds like one or more of following computers are always working, MPX body computer, MPX door computers ( each door has it's own computer and there are totally 4), tilt/telescopic computer and seat position control computer. Disconnecting one by one would be the way to troubleshoot. Remember that all these computers are getting power from the battery without any switch. Every time when you disconnect any of these, you need to remove the negative terminal of the battery. I'd start with the door computer which has the up/down problem.
Old 01-24-19, 10:36 PM
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Ryancucf20
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Originally Posted by Yamae
Sounds like one or more of following computers are always working, MPX body computer, MPX door computers ( each door has it's own computer and there are totally 4), tilt/telescopic computer and seat position control computer. Disconnecting one by one would be the way to troubleshoot. Remember that all these computers are getting power from the battery without any switch. Every time when you disconnect any of these, you need to remove the negative terminal of the battery. I'd start with the door computer which has the up/down problem.
got it! Thank you. I’ll take a look into it ASAP. Cause this whole thing has been an ordeal.

I dont think it would be my tilt tilt as it hasn’t worked the whole time I’ve had the car
Old 02-28-24, 07:10 PM
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PinnySkenis
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Originally Posted by Ryancucf20


got it! Thank you. I’ll take a look into it ASAP. Cause this whole thing has been an ordeal.

I dont think it would be my tilt tilt as it hasn’t worked the whole time I’ve had the car
Did you ever find out what the problem was? The MPX-B fuse is causing 600mA of draw for me and I’m grasping at straws trying to find a place to start. Thanks!
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