I have a 96 LS400. A few weeks ago my battery randomly drained overnight. Jumped it and didn’t have the issue again until today. Battery was dead after work. The gauge cluster is staying on when I shut the car off. Pulling the gauge fuse in kick panel fuse box shuts it off. Eventually it shut off like normal, after checking some fuses and relays. After about 20 minutes of being parked tonight, the headlights came on. They were on auto, turning them off worked fine. Just checking to see if anybody has had a similar issue or any ideas of what could cause this.
For background, car has 363k miles, ECU has been rebuilt, newer alternator and battery.

 

Sorry for your problem. I myself have no exact experience with your problem, but the MPX body computer may be related. Because your 2 separate symptoms of the gauge cluster and the head lights on are commonly controlled by that computer. One idea is to disconnect all connectors from it to distinguish the problem.

 

I will have to try this tonight. Do you know of a rebuild service for the BCM? Or if they have a common failure point? Thank you.

 

Sorry that I don't know about the current situations of the rebuilding service agents in your country since it's been a long time after I came back to Japan. If I were you, I'd try to fix the problem using equipments such as an oscilloscope, a logic analyzer, a DVM, signal generators, good soldering tools and my skills. I am a guy who enjoy doing it. Local dealer managers and shop owners often call me for a help when they encounter electronics related problems that require deep skills to fix. I just fix units just for my curiosity and it's free.

The MPX body computer has electrolytic capacitors which contain QAS and they often fail when aged just like capacitors in the ECU although those survive a bit longer due to the lesser stress and smaller ripple currents. See the photo below. Those capacitors are already removed. Other than those capacitors, relays (white square box ones) sometimes fail too caused by the worn contacts which show one side convex and the other side concave. It would be smarter to replace these parts before problems happen.

 

Thank you for the insight. Didn’t have time to try unplugging the unit to see if it turned the gauges off today. After looking through wiring diagrams, I’m hoping it’s a short in the junction box but we will see once I have time to dig into it. If it turns out to be the capacitors or relays in the
body computer, I may try contacting you to help me identify which parts I will need to fix it. If that is alright with you. Thank you again for the help.