Jmorgn

Hello esteemed LS400 enthusiasts,

I'm the owner of a 1999 Lexus LS400 and have recently encountered an intermittent overnight battery drain issue. To provide some context, both the battery and the alternator were replaced in February of this year. I've verified that the alternator is functioning correctly by measuring a consistent 13V output while the engine is running. Consequently, I decided to investigate potential electrical drains and discovered a notable amperage draw originating from the DOM (dome) fuse.

Despite extensive online searches and forum exploration, I've been unable to find comprehensive information on this specific issue. Admittedly, my expertise in automotive electrical systems is limited to basic knowledge, which makes deciphering a wiring diagram somewhat daunting at this stage. I'm hoping someone in this knowledgeable community could steer me in the right direction for diagnosing and fixing this issue.

A couple of additional notes that may or may not be pertinent:

1. My dashboard consistently displays a "tail lamp failure" message, despite the fact that I've replaced the bulbs in the affected rear passenger tail light with no success.

2. I'm also receiving a perpetual "trunk open" message on the dashboard, even though the trunk is securely closed.

These warning messages have been present for a few months and haven't significantly impacted the vehicle's drivability. However, I'm not ruling out the possibility that they may be related to the current battery drain issue.

Your insights and advice would be immensely appreciated. Thank you in advance for your time and expertise.

Thanks!

paulo57509

The DOME fuse feeds:

• Air Suspension ECU
• Airbag Sensor Assembly
• Body ECU
• Combination Meter
• Data Link Connector 1
• Diode (Rear Interior Light LH)
• Diode (Rear Interior Light RH)
• Diode (MPX Body No. 2)
• Front Personal Light and Garage Door Opener
• Ignition Key Cylinder Light
• Luggage Compartment Light
• Luggage Compartment Light Switch
• Noise Filter (Rear Interior Light LH)
• Noise Filter (Rear Interior Light RH)
• Power Seat ECU
• Radio and Player
• Rear Interior Light LH
• Rear Interior Light RH
• Rear Personal Light LH
• Rear Personal Light RH
• Rear Door Courtesy Light LH
• Rear Door Courtesy Light RH
• Step Light LH
• Step Light RH
• Vanity Light LH
• Vanity Light RH
• Wireless Door Lock Control ECU

The voltage you're reading across the DOME fuse can be in error depending on the way you're going about measuring it. This is a long video but quite informative.

Jmorgn

I appreciate it, that video was very informative.

I know back when I tested it, I used the second method. But i did not wait for the vehicle to “sleep” so I may have to revisit this method. It seems like I’m really going to have to just start testing each thing one by one. I hate electrical issues lol

thanks!

Edit: I realize one of my rear door locks do not work. Also, when I use the fob to lock the car, It sounds like the locks engage multiple times. Is it possible that could be the source of this issue? Maybe it’s trying to engage that last lock multiple times during the day? Idk just another shot in the dark