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I have been noting a parasitic battery drain and referenced the thread below. To give you a frame of reference the battery fully charged with a PulseTech unit showed 12.68 volts on 9/12/18. Before this test started it was reading 12.41 volts (both positive and negative leads connected). So in four days time it lost .27 volts. I had previously disabled the smart key but that had no effect on the parasitic drain rate. Although I purchased a fuse buddy I ended up looking for parasitic battery drain by simply measuring the voltage across the fuse. The only fuse which showed any amperage was in the trunk and its labeled 7.5 A RR ECU-B. The one caveat is that I was unable to determine how to power down the two rear trunk lamps. My multimeter was set to 2V DC and it read .005. Unfortunately this multimeter didn't have a convenient millivolts setting so I am unsure how many millivolts (or volts) the fuse is drawing and then where to go next to follow the fuse to RR ECU-B to see if I can isolate the issue. Thanks for your assistance.
Here's the electrical schematic that shows circuitry downstream of "7.5 A RR ECU-B". I have also attached the PDF if the schematic below is not legible.
I found your earlier post and it seems that the trunk lights were causing the amperage draw. If that was the only power draw (and I tested all fuses but not relays) then I am not sure what I should do next? Help.
Also, the Lexus battery is 3 1/2-years old but since it will pass all of the tests that the PulseTech charger has and charges up to 12.68 volts (and the alternator is working correctly) I wonder if the battery is simply losing its ability to maintain a charge?
Please note that it takes time for the LS430 to "go to sleep". Most of the systems on the LS430 do not turn off immediately when you turn off the ignition. Some lights will stay on after you turn off the ignition, and continue to be powered up several minutes after you close all the doors. Keep the above conditions in mind when you perform the parasitic battery drain test. For example, if you measure current draw by the trunk lights with the trunk lid open, you will always get a reading because the trunk lights are designed to stay on.
Thank You. Since I couldn't get the two trunk lights to turn off I knew there would be some amp usage. Unfortunately, the RR ECU-B is where the current flowed. Given that and noting that I couldn't find any other current draw in any of the fuses; what do you recommend that I do?
Just to add some real world and non-Lexus specific info...my uncle had an issue with his 2007 Acura RL that the dealer could not find (car dead after 3 days in garage, repeatable). Indie traced it to a faulty bluetooth module, which was then disconnected since uncle does not talk on phone anyway while driving...
If I leave the key off and bring my cell phone in and enable Bluetooth it doesn’t connect. If I were to start the vehicle the Bluetooth will connect. I’m not sure if this indicates that Bluetooth isn’t a parasitic power drain. Is there a way via a menu to disable Bluetooth?
I have been noting a parasitic battery drain and referenced the thread below. To give you a frame of reference the battery fully charged with a PulseTech unit showed 12.68 volts on 9/12/18. Before this test started it was reading 12.41 volts (both positive and negative leads connected). So in four days time it lost .27 volts. I had previously disabled the smart key but that had no effect on the parasitic drain rate. Although I purchased a fuse buddy I ended up looking for parasitic battery drain by simply measuring the voltage across the fuse. The only fuse which showed any amperage was in the trunk and its labeled 7.5 A RR ECU-B. The one caveat is that I was unable to determine how to power down the two rear trunk lamps. My multimeter was set to 2V DC and it read .005. Unfortunately this multimeter didn't have a convenient millivolts setting so I am unsure how many millivolts (or volts) the fuse is drawing and then where to go next to follow the fuse to RR ECU-B to see if I can isolate the issue. Thanks for your assistance.
FYI these cars seem to drain the battery quickly. I know if I leave my 03 LS430 for two weeks without disconnecting the battery it will be dead. I would not be surprised if you don’t find a smoking gun.
After testing the battery after it has been disconnected it only dropped .02 volts in two days and a load test showed the lowest voltage was 10.88. As soon as I hooked up the battery the parasitic drain started again. That got me to thinking that maybe the alternator diodes were failing and allowing a small drain. The alternator put out good voltage but is it feasible to pull the 140 amp alternator fusible link to determine if the drain is coming from the alternator? Has anyone done this test and have any results they could share?
Have you figured out what the source of your drain was?
Came to a dead battery on my car after 5 days of being parked and i just did a multimeter test and it shows about 3.3 amp draw.
I removed every fuse and relay and still had the same draw. Only ones that didn't budge were the big fuses next to the battery, i think those are bolted down if i recall correctly.
09-16-18, 02:25 PM
Parasitic Battery Drain-7.5A RR-ECU-B
