I have a amp draw question...and the "short" jumper in the fuse box - SOLVED!

UPDATE 4-20-2022
SOLVED!!!!
the body control module is awakened if the hood lacth is open OR something is plugged into the OBDII port!!! It the EUC-DDC is on, it pulls .5 amps!
If it is "off" (AKA times out and falls asleep) normal draw is .05 to .07.

Why did I missed this? I checked the OBDII port and I checked the hood latch but not at the same time! The Toyota tech did not tell me this - he just said I unplugged the OBDII without opening the door and the current went away! But I figured during his routine he must close the hood latch as a procedure.


So why do I have something plugged into the OBDII port? The android tablet Tesla style radio I have plugs in to the truck for system information.






I just bought a 2018 Tundra and the owner had a battery draw down issue when truck is sitting.
He said that after a week or two the battery would be dead.

I bought this one - https://www.tundras.com/threads/kino-the-tundra-the-more-we-explores-2018-toyota-tundra-build.32826/

what I have found.....
I put my amp meter in series between the battery and the power lead going to the under the hood fuse box and found a parasitic draw of .7 amps. It looks like the ECU is drawing .5 amps (I pulled the ECU 20 amp fuse). When I do this I see the amp draw go from .7 dc amps to about a .2 dc amps. Any ever have an issue, or know what the normal ECU draw is? Or what is the normal system amp draw when the truck is not in use?

BTW - to the common truck owner, if you disconnect this cable, you will see an arc of electricity with the draw.

 

For any additional equipment I put on my truck I run straight off the battery and put a relay to power that circuit and lately I use one of these

$15 Time Delay Relay 10 Seconds 5 pin 12V 30A 5 pin SPDT

https://www.amazon.com/gp/product/B0744HSF8P?ie=UTF8 which gives it a 10 second delay to protect, in my case, a ham radio from any voltage spikes at startup.

 

Good info…. All of my accessories have be tested and are pulling zero amps. They are tied to the fuse box 150 amp aux bolt on connection point.

 

Congrats on the buy! That sale didn't drag out at all....

Maybe @RainMan_PNW can help you as he seems pretty good with wiring etc

 

Ahhh, never realized the guy who did the WNOR slider install video was a member on here. Looks like you got a great truck!

sorry I can’t be of help with your parasitic draw, but .7 amps sounds like quite a bit. Sounds like you have good electrical experience.. I’m sure you’ll figure it out

welcome!

 

Have a 2018, there is definitely a parasitic draw by the ECU due to the EVAP system etc., but never measured it so not much help. Do know that having the hood open causes a draw though, can lock the latch with a screwdriver to eliminate if need in case you haven’t.

 

Hopefully my neighbor will let me test his truck to compare to mine. I will keep you all posted. Anyone have the time to check theirs?

 

My 2018 sometimes sits for 6 wks. w/o starting or battery tender. Still starts right up w/ 2018 factory battery. Only has 9,100 miles on it, maybe that is why I have not had problem. 34ford

 

Just checked mine, was between .5 - .6 dc amps.

 

Can you clarify exactly how you checked the amp draw? It would be best to use a clamp style probe you hook over all of the wires coming off of the positive post. If that’s what you did I’m sorry I didn’t understand.

 

If one uses a meter in-series with the circuit, that is much more accurate than a clamp on dc meter. I have both.

EDIT: did not mean to be an ass here, but when searching for tiny current draw its more precise and high resolution - .1 amps vs .01 amps

 

Thanks a million guys!!! I will keep and eye on it. The issue may be a bad battery.

BTW- One can looses current via a dirty battery top. If there is excessive dust and moisture it will conduct across the top. You can prove this theory with a meter. Connect the (-) to the negative battery post and poke around the top with the positive . you see voltage? you are losing energy.

here for the clamp on guys.... note the wire that I am on. This is the wire that supplies energy to the fuse box. The second cable reads 0.0 - I am sure that feeds the start relay. No issues with current draw (leakage) there.


Checking the balance and proving the current draw via ONE of the chassis grounds - there are two.

 

Other than checking against a few other rigs, I don’t have any real feedback.
I’ve read various places that if you’ve got an OSB scanner/gage/reader plugged in, you’ll experience parasitic draw. Going through the EWDs you will definitely see things on various systems (including main ECU) that use BAT power - your immobilizer and and security systems all need it. But what that actual draw is, no idea

 

A few other things to think about, pretty sure once the key is turned off the truck goes to "sleep" after about 15 minutes. I remember reading about people accidently turning the cargo light "ON" and noting it only went off 10-15 minutes after parking the truck. Might be worth checking the draw after the timeout 15ish minutes and seeing how much it drops. This reading would be move of an accurate long term draw value. When the truck goes to "sleep" the only systems still running should be security, key fob recognition, and a few other things to save memory data in computer chips. (Fuel mileage data, radio presets ect)

What the acceptable value is from Toyota I am not sure, however I would think you only want a few hundred milliamps (.2-.4 Amp) of draw long term. I could measure mine sometime to just to see for fun. I might also look in the repair manual to see if Toyota gives any values.

I keep an added on microcontroller powered 24/7 in my truck. It draws an additional 100 milliamps (.01 A) on top of the factory wiring. I have left it a full week or more with no problems starting this is a relatively decent load added on.

Even with a steady .5 Amp drawn a good battery should be able to sit for a week or two if not more and still be able to start the vehicle.

 

^^^^^^^^
A decent battery should be able to sit a couple weeks with even a little draw. I'd check the battery!
Cheers

 

I think the sleep mode is a good theory - that the .5 current should drop after a timeout function. If you think about it, with a .5 draw on a 100 amp hour battery at 100% efficiently it would be dead after 200 hours. 8.3 days. I will open the hood, to disable the hood switch, close the truck door... come back in during the day and check every few hours...
Learning as we go!

 

I went through this same issue. Battery would not start the truck after sitting 4-5 days. I still had the original battery in the truck at the time. I had heard a lot of negatives about Toyota batteries so I just replaced it. The OEM battery was only two years old but I never had another issue after I changed it.

 

well first test this morning current draw .5 / Battery voltage 7.5. Installed a new battery draw is constant after hours batter voltage a 12.44

 

found this..... I have been leaving my hood open.... but I have no lights on under the hood. I have been leaving it open to not activate the dome lights, also thinking that a door switch could activate or "wake up" the ECU. Some diesel do this, open the door and it turns on the glow plugs.

Also someone said it could be a bad diode in the alternator.... unplug and see what happens.....

 

OK update.... I force closed the hood latch (there is a switch in it) , ensured no lights on in the truck.

Its the ECU pulling all the amps (confirmed by removing the 20 amp under the hood relay box fuse). Average .5 with the battery at 12.3.

an assumption... the ECU 20 fuse powers the ECU and the ECU-B . So....Also pulling the "SHORT" (transportation (disable radio, dome light, etc) fuse) stop my current draw. I think the ECU powers the ECU and the ECU-B and some I aftermarket item in the truck is drawing on the ECU-B (body control module).

I totally disconnected the aftermarket android dash radio - still a draw. Afetr market light bar? it ties to the harness I think??

 

Any one know what the "short" Pin feeds power to? I read the radio and the Dome light? and ECU-B? I wonder if there are down stream fuses I can pull to isolate the issue?

note to self...

 

see this below.... if the is correct for my 2018....
looks like the "SHORT" feeds the "ECU-DDC" pin right below it..... when either is pulled the current draw problem goes away.


follow the diagram and it feeds these 3 fuses....

 

I literally just answered this question here. Read the last few post but this was from a 2014-2017 diagram

https://www.tundras.com/threads/fuse-not-getting-power.105988/

The short pin is designed to be removed for long term storage or shipment. It kills things like dome lights, door locks and wireless receiver ect.

I can pull up the 2018 diagram tomorrow and see exactly what the short pin links power too

 

I see you are in my deep and are very close to isolating the draw. I would wire brush the inside of your battery terminals and do the same on the chassis ground. Remove everything and clean it first then tighten it all up. Make sure the door switch is "off" and hood latch is closed. Try and locate the ECU's ground point and double check that too. Any chance there was any onboard monitoring or connected services, remote start? Also double check all bulbs and lights, if you have anything out or possibly shorted, it may cause a draw.

 

Been reading along and was reminded of a battery drain issue common to the VW new Beatle. My Mom had a '06 that would arbitrarily kill the battery seemingly just for the fun of it.

VW had a procedure of checking for a voltage drop across a fuse in order to isolate which circuit was passing current through the fuse. It had good sense but does require a VOM substantially better than your average Harbor Freight offers.

I was still working then and had access to goid Fluke so some probes were modified in order to poke inside the test holes on the fuses. Mind you the readings you are looking for are in millivolts but I was able to isolate which circuit was causing the problem. It turned out to be the Monsoon radio amp and if she left the radio on when the car was turned off the amp remained on. Turn the radio off first, no problem.

Anyway, I have long since deleted the troubleshooting info since she sold the car but with a little Google-Foo you should be able to find the procedure.

 

Here is the entire circuit controlled by the "Short Pin" on the 2018+


Short Pin >>> 20A ECU-DDC >>> 15A Radio, 5A ECU-DDC NO. 1, 5A ECU-DDC NO. 2

The 30A AMP fuse is also on there but I dont think it is your issue as its parallel to the 20A ECU-DDC




As stated above checking for a milivolt drop across these 4 fuses could help isolate which is your problem. You could also just pull them one by one and see which one removed causes the Amps to drop significantly. That will tell you which circuit to focus on. Unfortunately I would lean toward the ECU-DDC No. 2 which controls a large amount of things interior wise. Could be hard to narrow down which it is exactly.