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Help! 1997 ES300 Parasitic drain on battery and tracked it down to the ECU-B 10A fuse

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Old 08-19-13, 08:20 PM   #1
Ickey
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Default Help! 1997 ES300 Parasitic drain on battery and tracked it down to the ECU-B 10A fuse

I just purchased a new battery 3 months ago. I left my car off for 3 days and next thing you know, the car is completely dead, no lights, anything. I had the autoparts store check the battery and they said the battery is fine. So I did some troubleshooting myself...

My battery was drawing about 85 milliamps when the car is off. I basically went through and pulled each fuse and found that when I pulled the 10A ECU-B fuse, it dropped down to 15 milliamps.

Anyone know exactly what the ECU-B fuse controls?? Also, is there anywhere else down the circuit I can troubleshoot to figure out exactly what's going on? Do I need to just replace the ECU (the one located behind the glovebox??

I have googled and searched multiple forums for a couple hours and I can't seem to find any answers regarding this specific fuse and what it controls or how to fix.

Any help would be appreciated. Thanks in advance!!
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Old 08-19-13, 10:59 PM   #2
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Originally Posted by Ickey View Post
I just purchased a new battery 3 months ago. I left my car off for 3 days and next thing you know, the car is completely dead, no lights, anything. I had the autoparts store check the battery and they said the battery is fine. So I did some troubleshooting myself...

My battery was drawing about 85 milliamps when the car is off. I basically went through and pulled each fuse and found that when I pulled the 10A ECU-B fuse, it dropped down to 15 milliamps.

Anyone know exactly what the ECU-B fuse controls?? Also, is there anywhere else down the circuit I can troubleshoot to figure out exactly what's going on? Do I need to just replace the ECU (the one located behind the glovebox??

I have googled and searched multiple forums for a couple hours and I can't seem to find any answers regarding this specific fuse and what it controls or how to fix.

Any help would be appreciated. Thanks in advance!!
I have the same problem on my 98 es300. I never found out what it was but i just pulled the fuse out and car runs fine with it. I did get a funny feeling it might have some connection to the airbag system and stuff based on a diagram I once saw. Hopefully someone knows what this is , as I am sure it is not the main ecu
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Old 08-19-13, 11:02 PM   #3
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I have the same problem on my 98 es300. I never found out what it was but i just pulled the fuse out and car runs fine with it. I did get a funny feeling it might have some connection to the airbag system and stuff based on a diagram I once saw. Hopefully someone knows what this is , as I am sure it is not the main ecu
I found another post that says it is related to the anti theft, door locks, security system.

But lets just wait for others to confirm this
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Old 08-21-13, 10:02 PM   #4
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Thanks for the replies. Yes, I've also read that it has something to do w/ the anti-theft system.

But when I read the book (Haynes Repair Manual) and look at the electrical system diagram, I only see two circuits that use the ECU-B fuse: Cruise Control and the Power Seat.

I could be completely wrong. Hopefully someone can chime in.
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Old 08-22-13, 08:23 PM   #5
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Try removing the charge wire from the alternator and check for a draw there. Sometimes jump starting a car with a dead battery can overheat the diodes in the alternator and cause them to leak. Also the car doing the jump starting should not be running for the same reason. Try getting an alternator to run a starter in a car all by it self... you will let the magic smoke out of it.
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Old 08-23-13, 12:56 AM   #6
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when looking at a current flow chart for the 1998 es300, it seems like a/c control assembly, airbag sensor assembly, the srs warning light, combination meter, cruise control ecu, data link connector 1, and seat position control ecu are reliant on the ecu-b 10a fuse.

hope this helps, i haven't done much electrical work aside form reading diagrams, so hopefully someone else can give you some ideas on how to possibly fix this.
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Old 08-23-13, 02:35 PM   #7
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Yes most of those systems are active when the key is off and can backfeed a bad diode in the alternator.
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Old 08-23-13, 11:42 PM   #8
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Thanks for the replies and the extra work on finding out what circuits go through the ECU-B fuse.

I'll definitely start w/ testing the alternator. Also, my AC unit has been iffy lately, which may be causing it. The AC unit in the car will flash green and after 15min, it will start blowing cold air.

I'll try a couple things. Probably start w/ the alternator first, then work my way around to different areas.

For now, I have my battery unplugged so it should still have pretty much a full charge. Been unplugged for about a week now, so this should help w/ the testing.
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Old 08-24-13, 07:39 AM   #9
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I

My battery was drawing about 85 milliamps when the car is off. I basically went through and pulled each fuse and found that when I pulled the 10A ECU-B fuse, it dropped down to 15 milliamps.
Hi Ickey. How did you determine this ? Did you touch the two leads of your volt meter to the postive and negative terminals of the battery ? Once before and once after you pulled the 10A ECU-B fuse ?
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Old 08-29-13, 11:07 AM   #10
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Hi Ickey. How did you determine this ? Did you touch the two leads of your volt meter to the postive and negative terminals of the battery ? Once before and once after you pulled the 10A ECU-B fuse ?
I disconnected the negative terminal from the battery, then touched one of the volt meter leads to the neg terminal on the actual battery, then touched the other volt meter lead to the neg battery terminal connector (car side), then noticed the drain. While connected, I think removed each fuse individually to find the one that is causing the drain. When I pulled the ECU-B 10A fuse, the drain dropped dramatically.
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Old 07-19-14, 08:45 AM   #11
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I had what sounds like the same problem on my 1998 ES300: dead battery after returning from 9 day trip: seems OK after jump starting except current drain at negative battery terminal was about 88 ma with ECU-B fuse in & 24 ma with it out; found stuck seat set switch (mentioned in another post) & now get about 24 ma with all fuses in.

Did Ickey find his problem (85 ma with ECU-B, 15 without)?

Any other comments or suggestions, other than waiting a few days to see if problem returns?

I've seen a few posts about intermittent problems & am trying to sell the car, so I'd like to know as much as possible about it ASAP (don't want to wait 9 days without driving it again). I had the alternator & battery replaced recently so I'll take it back there to re-check the alternator in case jumping it damaged the diodes.
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Old 07-19-14, 09:54 AM   #12
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ECU-B is the ECU 's (constant) memory power connection. The ECU learns each time the car runs, it saves what it learns. If you disconnect the ECU-B fuse, the car will still run fine, but it will be back to re-learn mode each time you drive it. It takes about 5 minutes for the ECU to learn the engine, and it needs some highway driving to complete it.

15 milli amps, out of an 85 milliamp drain is not a considerable drop. a 70 milli amp drop (the real power drain) would be a huge drop. Car's use the battery power when they are just sitting around, that's normal.
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Old 07-20-14, 04:49 PM   #13
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ECU-B is the ECU 's (constant) memory power connection. The ECU learns each time the car runs, it saves what it learns. If you disconnect the ECU-B fuse, the car will still run fine, but it will be back to re-learn mode each time you drive it. It takes about 5 minutes for the ECU to learn the engine, and it needs some highway driving to complete it.
That's good to know, thank you for sharing.

Seems like the seat memory switch is a common issue, as I noticed it on my car as well.
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Old 07-20-14, 04:49 PM
 
 
 
 
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1997, 2003, 97, ac, battery, car, control, discharge, drains, draw, drawing, ecu, es300, fuse, fuses, lexus, parastic

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