Parasitic Draw (ECU-B)

[HeelsFan72]

Hi all, need some help with a parasitic draw I’ve been having on my 2018 SR5 Premium. This started with a struggling 2 year old TrueStart battery this winter. Realllly sluggish to crank especially on cold mornings. Replaced with a X2 power group 24F AGM battery. Figured 2 years was too short of a lifespan for a battery so went looking for a draw.

I’ve consistently found 180 mAmp draw on the vehicle. This is present from ~30 min after shutting the vehicle off all the way til the next morning. Consistent with all aftermarket electronics removed from battery power and everything unplugged. I’ve got no remote start, smart key, aftermarket anti-theft, or anything of the sort that should be drawing.

We isolated the majority of this draw to the ECU-B circuit, as it drops to ~40-60 mAmp when the 10A ECU-B fuse is removed. Here’s where it gets interesting.

I have a friend with a 2016 TRDOR and his neighbor has a 2020 SR5. On all 3 vehicles that had sat for 2 hr+ we found a 120-180 mAmp draw, and the draw dropped by ~120 mAmp when the ECU-B fuse was removed. That would lead me to believe that was normal… but it seems like a lot of draw for the computer to be pulling on a shut off vehicle. It’s also producing noticeable drop in my battery voltage (13>12.5V overnight vs no drop with battery disconnected).

So I still feel like there’s some inappropriate draw here, but I can’t make sense of why we replicated it on 3 separate T4R.

So I guess a couple questions:

- Does anyone have hard data on their draw with their 5th gens? Is the reported ~50 mAmp draw actually normal? Or are all our vehicles pulling ~120 mAmp on the ECU-B circuit all the time?

- Does anyone have a list of the electrical components on ECU-B. I already know it’s going to be a bear, but I need an exact list before I start tracking it down.

- Does anyone have advice on how to go about hunting this down on the ECU-B circuit. It feels a daunting task.

Thanks in advance!

 

[HeelsFan72]

So update… not surprisingly, when you connect the leads in-line with the negative cable and post, it turns the computer back on. What IS surprising (to me at least) is how long the computer stays active. I figured it would be a couple minutes, but turns out it’s nearly 20. After taping the leads on the cable and post, sometime between 15-20 minutes after that my draw drops to 50-60 mAmp.

So I don’t appear to actually have a draw from the ECU-B fuse. Now I need to decide if 50-60 mAmp draw is problematic and worth tracking down. Thoughts?

 

[fkheath]

So I don’t appear to actually have a draw from the ECU-B fuse. Now I need to decide if 50-60 mAmp draw is problematic and worth tracking down. Thoughts?

A typical car battery has 50 to 75 amp-hours capacity. A draw of 50 ma of current will take 1000 hours to deplete the battery, or 42 days. (50 amp-hours ÷ .050 amp ÷ 24hours/day).

 

[rwrobs777]

Hi all, need some help with a parasitic draw I’ve been having on my 2018 SR5 Premium. This started with a struggling 2 year old TrueStart battery this winter. Realllly sluggish to crank especially on cold mornings. Replaced with a X2 power group 24F AGM battery. Figured 2 years was too short of a lifespan for a battery so went looking for a draw.

I’ve consistently found 180 mAmp draw on the vehicle. This is present from ~30 min after shutting the vehicle off all the way til the next morning. Consistent with all aftermarket electronics removed from battery power and everything unplugged. I’ve got no remote start, smart key, aftermarket anti-theft, or anything of the sort that should be drawing.

We isolated the majority of this draw to the ECU-B circuit, as it drops to ~40-60 mAmp when the 10A ECU-B fuse is removed. Here’s where it gets interesting.

I have a friend with a 2016 TRDOR and his neighbor has a 2020 SR5. On all 3 vehicles that had sat for 2 hr+ we found a 120-180 mAmp draw, and the draw dropped by ~120 mAmp when the ECU-B fuse was removed. That would lead me to believe that was normal… but it seems like a lot of draw for the computer to be pulling on a shut off vehicle. It’s also producing noticeable drop in my battery voltage (13>12.5V overnight vs no drop with battery disconnected).

So I still feel like there’s some inappropriate draw here, but I can’t make sense of why we replicated it on 3 separate T4R.

So I guess a couple questions:

- Does anyone have hard data on their draw with their 5th gens? Is the reported ~50 mAmp draw actually normal? Or are all our vehicles pulling ~120 mAmp on the ECU-B circuit all the time?

- Does anyone have a list of the electrical components on ECU-B. I already know it’s going to be a bear, but I need an exact list before I start tracking it down.

- Does anyone have advice on how to go about hunting this down on the ECU-B circuit. It feels a daunting task.

Thanks in advance!

Unless the max draw is spelled out in Service Info you can use the RC of the battery in minutes divided by 4....100 minute RC max draw 25 milliamps.