Auxiliary battery?

[woodardl08]

I’m being told by a service manager that because I have an auto stop start feature on my 21 3.5L ecoboost that I have a second auxiliary battery. My auto stop start has never worked, so if I have one I think it is dead. I have watched videos and it says it was behind the passenger side rear seat. All that is there is an inverter…. Do I have a second auxiliary battery??? If so where is it??

Sponsored

 

[DadBald]

It would be under the passenger rear seat, not behind it. Its only used to power the vehicles 12v systems when the main 12v battery is preoccupied with the engine starter, so very briefly and not frequently at all. I don't think your auto start/stop would be affected by it, rather everything else would flicker when the starter was engaging. This is speculation tho. Otherwise the two batteries are connected in parallel all the time.

Edit: here's a good summary video

 

[Ricksc]

My 2017 did not have a second battery. I would think your battery is weak. That would cause ASS not to work. Any other weird electrical issues? Deep sleep? ASS was deleted on my 22. I did have a bad OEM battery. My truck would go into deep sleep regularly. I updated to a H7 and reset the BMS no issues after that. Measure your battery voltage after about a hour of shut down see what it reads

 

[Ricksc]

I believe that aux battery is on power boost models. Never had one on my eco boost

 

[woodardl08]

My 2017 did not have a second battery. I would think your battery is weak. That would cause ASS not to work. Any other weird electrical issues? Deep sleep? ASS was deleted on my 22. I did have a bad OEM battery. My truck would go into deep sleep regularly. I updated to a H7 and reset the BMS no issues after that. Measure your battery voltage after about a hour of shut down see what it reads

It’s reading 12.4 volts after about an hour.

 

[Ricksc]

That’s not too bad. Have you driven a long drive and see if it works? Have you tried turning it off and back on? Honestly I would be happy it doesn’t work. I found in my 2017 if you didn’t hold the brake peddle all the way down it would not work too.

 

[woodardl08]

It would be under the passenger rear seat, not behind it. Its only used to power the vehicles 12v systems when the main 12v battery is preoccupied with the engine starter, so very briefly and not frequently at all. I don't think your auto start/stop would be affected by it, rather everything else would flicker when the starter was engaging. This is speculation tho. Otherwise the two batteries are connected in parallel all the time.

Edit: here's a good summary video

 

[Ricksc]

The power inverter is for the power outlets in the truck. AC power outlets

 

[Fox146]

The aux battery is powerboost only. The stop start not working more than likely because of a low voltage issue. Willing to bet if you charged or changed your battery it will work

 

[DadBald]

Ah, I see. Powerboost has the inverter under the truck I think, and an aux battery in that spot where your inverter is. Maybe you don't have an aux battery.

 

[Ricksc]

Only power boost has the auxiliary battery. No power boost no battery

 

[Kanuck]

I’m being told by a service manager that because I have an auto stop start feature on my 21 3.5L ecoboost that I have a second auxiliary battery. My auto stop start has never worked, so if I have one I think it is dead. I have watched videos and it says it was behind the passenger side rear seat. All that is there is an inverter…. Do I have a second auxiliary battery??? If so where is it??

A second battery is only on the powerboost trucks. ASS not working is a sign of a low SOC on the main battery or if you bought it used, the ASS maybe turned off with Forscan by the previous owner.

 

[Ricksc]

ASS can not be turned off with forscan. There could be an after market bypass installed. It plugs in to the switch

 

[Kanuck]

ASS can not be turned off with forscan. There could be an after market bypass installed. It plugs in to the switch

Yes it can...do the research.


Check the common page on this spread sheet...lines 9 and 10
https://bit.ly/3cJnYMS

 

[jhelrey]

Go to your screen settings in front of you, toggle to MPG data, then scroll to ASS. It will tell you why it's not working.

I bet $ on your main battery.

Sponsored