Figuring out parasitic drain

Hello, picked up a 2016 TRD OR recently that is getting a dead battery after a week or less. Recharged it and it drained again. Tried a second battery and still saw voltage dropping overtime. Before I start modding it I want to address this drain. Looks like previous owner had a lightbar on the front and a tow light.

Stuck a multimeter between the negative terminal on battery and measure around 500ma draw when the truck is off and the keyfob is far away (and the hood and doors closed). Started pulling engine fuses and found the ECU-B no. 3 fuse drops the amps so did more searching and saw ECU-B is used by a bunch of components so put fuse back in and pulled fuses in the cabin and eventually removing AM2 no. 2 and MPX-B fuses brings the amps down to about 40ma (AM2 no. 2 removes 95% of the draw).

Checked wiring diagram to see these are connected to the certification ECU with the smart key and when pulling the C29 wiring harness on the ECU, almost all the amps drop. Checked voltage on pin 10 and was within range (~12.6v) and then tried checking resistance on pin 11 but got values between 1-4ohms so I'm not sure if there's an issue or my dvom probes are just not well.

The truck seems to function properly for the most part from what I can tell. Sometimes the driver handle doesn't unlock when touching it after a night of being parked until I unlock the truck with the keyfob, then I'm able to lock and unlock with the handle.

Trying to work with dealership and address the parasitic draw under CPO, but looking for any other ideas. Thanks.

 

Are you waiting at least 2 hours after 'power down' before checking?

https://www.tacomaworld.com/threads/ma-draw-w-truck-turned-off.644085/

 

Is there a remote start module or a drone remote start left in there? The older ones could cause the drain.

 

The other possibility is that you have a bad alternator that is causing consequential damage to both batteries.

You seem on top of it though, so while not likely, worth adding to the thread for posterity.

 

Thanks all for suggestions. I had pulled all the fuses in the cabin before my first message then it rained so I waited till today to put them back. Now I tried another inline amp test and note that the draw was still around 500ma initially then after 15s or so it drops to about 250ma, then after a minute drops to 60-70ma which is acceptable. I'm not sure why this didn't happen before, but its likely when I tested with keyfob far away, I must not of been doing the inline test. Can the amps come back up within that two hour timeframe? I think at most I was measuring amps for about 30min, but after seeing the drop to acceptable levels I stopped after a few minutes now.

Every time I moved close to the driver door the amps went up which was due to me having the key fob in my pocket, and moving to the front of the truck started the amp drain again back to 60-70ma so I might not have a parasitic draw. I tried seeing if the truck would remote start with the three lock presses but it didn't, though I haven't checked for any added wiring under steering column yet (only junction box area).

I then checked DC voltage a couple times when engine was on and off. Started around 12.36v which is low, then 13.94v turned on. I never saw over 14v when on or revving the engine and when off after an hour, dropped to 12.42v. I swapped in the original battery that has been sitting in the garage for 3 weeks that had a voltage of 12.82v before I put it back in, and turned on was around 13.9v. I turned on lights, fans, and radio and the volts only dropped to around 13.87v. Then checked AC voltage and was getting ~360mV AC which means the alternator appears to work(?) (I'm not sure). I was following the alternator test suggestion from https://www.toyotanation.com/threads/best-way-to-test-alternator.330026/#post-3063176.

I'll check DC voltage again in the morning to see how low it's gone.

 

Are you sure the batteries yo are swapping are 100% OK (i.e. new?). Another thought ... When buying a new battery the shops usually have a tester they use to ensure battery, charging etc. I assume these check for Drain as well ???? Might be worth having this done ??? Just asking / My opinion ... But, you sure seem to have checked everything !!

 

I don't think you mentioned that you completely disconnected the previously installed light bar and tow light? If not, I would.

 

Ya I unplugged everything connected to the batteries. The new one was manufactured 01/20 and the original was 11/19. The original one is still holding at least 12.6v each morning but I should drive my other vehicle and see what happens over 2 days of sitting.

 

I usually start by confirming it, which you did, then second step, capacitive discharge for at least a few minutes. Sometimes ya get lucky and everything falls back into place hah

 

Hi, did you ever figure out your problem? I also have about 500 mA draw on ECU-B NO.3. I just installed a new stereo and a remote start. I think it's the remote start.

 

Not really, but it ended up going away after I unplugged all the offending cables and wiggling them around and let the system drain.

Now I have remote start and its working fine.

 

Ok thanks for the quick reply.
Is it this one by chance?

$160 Start-X Remote Starter Kit for Tacoma Push to Start 2016-2019 || 3X Lock to Remote Start || USA Brand

https://www.amazon.com/Start-X-Toyo...rds=tacoma+remote+start&qid=1610319372&sr=8-3

 

Yes, same one.

 

Hey bhamham, did you find the cause of the parasitic loss? I'm dealing with this too. I have a Viper remote start alarm as well. Should I focus there?

 

I did get rid of the parasitic draw but not really sure what was causing it, just what I mentioned above for testing. Since then I haven't had any issues with leaving the truck parked for a week or two. If the alarm connects with the other OEM wiring connectors under the dash, testing without it would be useful.