200ma parasitic drain ECU-B

[jupiterxing2044]

First, thanks for the amazing community. I've accomplished a ton of DIY work on my truck thanks to all of you.

This one has me stumped.

Vehicle:
05 Lexus GX470 w/ 147k

Notable mods:
1) Replaced air suspension w/ coils and struts front and rear at 80k
2) Using the secondary air injection bypass

Situation:
Battery goes dead after about 7 days (battery is 18m old Panasonic from Toyota)

What I've done:
Took battery to Toyota and they tested it on their bench with no faults

We narrowed down a draw on the 10A ECU-B fuse that measures between 1.3mv and 1.5mv across this fuse while truck is at rest. Using a voltage fuse draw chart that equates to 175ma to 200ma draw. All other fuses in the engine bay measure 0mv at rest.

I want to start troubleshooting but am unsure the best way to go about it as this fuse seems to "operate a lot of electronics" according to Toyota.

1) Where can I find a wiring schematic for this fuse?
2) Any recommendations on how to go about troubleshooting?

Thanks again in advance!

 

[tom4416]

What is your total parasitic draw as measured at the battery? There is always some draw in today's vehicles to maintain computer settings, radio settings, clocks, etc.. 200mah sounds high but I'd be interested in what it actually reads at the battery in total. Friend has a RAV4 that draws 140mah and Toyota tells him that's within the normal limits for that car but it also doesn't kill his battery in anywhere near 7 days - he's parked it at the airport for three weeks without coming home to a dead battery.

 

[metramm]

I would love to know where you got a 18 month old (new) panasonic battery for your lexus from.

I'm sure lots of folks on here would be interested as well!!!!

 

[jupiterxing2044]

I would love to know where you got a 18 month old (new) panasonic battery for your lexus from.

I'm sure lots of folks on here would be interested as well!!!!

I stand corrected. It's a "Toyota Truestart" battery. At some point I thought I heard those were made by Panasonic so that must have stuck in my head.

Still open to suggestions from anybody that has had a similar issue on ecu-b drain.

 

[RivMan]

They seem to be correct about operating a lot of electronics, see below. I can't find a good schematic of everything it runs, but it looks like it's pretty much any White / Red stripe wire in the car.

I'd start by disconnecting components one by one until you find the offender. Alternately you could take a current clamp, and find any white / red wire with current flow to find the offending circuit.

Good luck!

-Rob

 

[jupiterxing2044]

They seem to be correct about operating a lot of electronics, see below. I can't find a good schematic of everything it runs, but it looks like it's pretty much any White / Red stripe wire in the car.

I'd start by disconnecting components one by one until you find the offender. Alternately you could take a current clamp, and find any white / red wire with current flow to find the offending circuit.

Good luck!

-Rob

Wow! Thanks for posting that. My initial reaction is :yield:

I was hoping for a handful of things to check but this list is pretty wide ranging

I need to think about this a bit. I haven't used a current clamp but understand it in principal. Somehow I'd have to find the different wiring looms that branch off of this fuse to the different subsystems. :frusty:

 

[RivMan]

I would start at the other end. Find the Red / White wire at it's endpoint, and check the current.

I'd start with anything that may have an aftermarket accessory tapped into it.

I bet you find the issue fairly quickly. I have access to the factory service info if you need any specific questions answered.

-Rob

 

[jupiterxing2044]

I would start at the other end. Find the Red / White wire at it's endpoint, and check the current.

I'd start with anything that may have an aftermarket accessory tapped into it.

I bet you find the issue fairly quickly. I have access to the factory service info if you need any specific questions answered.

-Rob

Thanks Rob. The only two things I can think of that are modifications to factory are:
I removed the air suspension and replaced w/ standard suspension
Secondary air bypass

Maybe it's related to the air suspension? I found this blurb:
" Three fuses and one relay protects the AHC electronics. These components need to be checked and replaced when necessary. There is a 50 Amp compressor fuse, and 10 Amp air suspension fuse located in the main under hood fuse panel, with the AHC relay located in a sealed box attached to the side of the panel, and a single 20 Amp TEMS fuse under the dash."

So I'll check those out.

 

[jupiterxing2044]

I was hoping that it was something with the air suspension. I did find that only the relay was removed and not the other 3 fuses. Removed those and still have the drain on ecu-b.

There is 22 subsystems that run off of this fuse.

I just looked at the driver's side fuse panel on the inside:
Lexus GX470 (2003 - 2004) - fuse box diagram - Auto Genius

and noted that many of the fuses have same/similar description to what is listed in ecu-b image posted above.

silly question, is the ecu-b a master fuse for the systems on that indoor panel?

If that's the case, maybe my next step is to lock the vehicle down with the door open (but with the switch held shut) and check for any voltage across the interior panel fuses?

 

[truckhigh]

you probably hooked up the bypass to a constant instead of an ignition. some thing is probably just grounding maybe something with the vsc wires when you did the swap. Its the only related things to what you have done from the chart above. good luck because i hate these kind of problems.

 

[RivMan]

I was hoping that it was something with the air suspension. I did find that only the relay was removed and not the other 3 fuses. Removed those and still have the drain on ecu-b.

There is 22 subsystems that run off of this fuse.

I just looked at the driver's side fuse panel on the inside:
Lexus GX470 (2003 - 2004) - fuse box diagram - Auto Genius

and noted that many of the fuses have same/similar description to what is listed in ecu-b image posted above.

silly question, is the ecu-b a master fuse for the systems on that indoor panel?

If that's the case, maybe my next step is to lock the vehicle down with the door open (but with the switch held shut) and check for any voltage across the interior panel fuses?

Looking through the circuit diagrams, this does not seem to be the case. The ECU-B fuse feeds a White/Red wire that splits though a number of junction boxes and splices to feed individual circuits.

-Rob

 

[jupiterxing2044]

Looking through the circuit diagrams, this does not seem to be the case. The ECU-B fuse feeds a White/Red wire that splits though a number of junction boxes and splices to feed individual circuits.

-Rob

My test over the weekend confirmed that there isn't any measurable current flowing through the interior fuse panel.

 

[jupiterxing2044]

My test over the weekend confirmed that there isn't any measurable current flowing through the interior fuse panel.

**Found the problem**

I was finally able to figure out the problem by putting the truck in the garage, shutting off all lights (normally it's outside). It's my master window control switch - the lights on the master switch stay lit even after the vehicle goes to sleep. They are very faint so I just completely missed it up until now.

A few years ago that I had my master window switch control go out.

I ordered another one from a place called "switchdoctor.net" and installed it, never looking back as the switches worked.

Unplugged the switch and there is no longer a measurable drain across ecu-b :clap2:

Checked the plugs - no corrosion at all, everything is clean.

So I'm unsure if it is the switch or something up stream. I'm going to see about getting another switch from switchdoctor as they offer a lifetime warranty.

Any good way to remove the light while retaining the switch (maybe the red/white wire) while I get a replacement?

thanks to all those that helped!

 

[RivMan]

I believe the illumination circuit is separate from the power circuit causing you problems, and that the issue is probably an internal short inside that switch module. If the illumination is on when it shouldn't be, and no other modules are lit up, I'd open up the module and see where the lights are getting power from.

Glad you found it!

-Rob

 

[jupiterxing2044]

I believe the illumination circuit is separate from the power circuit causing you problems, and that the issue is probably an internal short inside that switch module. If the illumination is on when it shouldn't be, and no other modules are lit up, I'd open up the module and see where the lights are getting power from.

Glad you found it!

-Rob

Thanks Rob - switchdoctor is going to replace it for free and hopefully that will solve the issue. They said it was an old part #. And thanks for your help earlier as well! It definitely helped me in troubleshooting.