2018 2.7L, new batt, 12.7v with truck off. occasionally won't start after short trips

running, voltage is 13.25 at batt, regardless of load, understand it is supposed to be 13,5 to 14.8 .. no indicator lights. Any other diagnostics? do i need an alternator?

 

Will not start, as in no cranking at all or slow cranking?
13.25 vs 13.5 could be a the meter accuracy.
Did you test it with the headlights on?
Last thing is these trucks do use a battery monitoring system which I think can throttle back the charging.
I'm not sure of how to get around that for a test.

 

My friends ‘15 has this issue, but does have warning lights and a P0620 code. It seems damage to the wires from the alternator to the plug near the battery is pretty common. You’ll find good videos on YouTube about troubleshooting if you search that code.

 

I would suspect the BMS not asking for enough current in that case before I'd suspect the alternator.

Have you added any electronics that pull current while the truck is parked? I'm fairly sure my dashcam doesn't help my case, and it's only a real issue when I do a lot of short drives.

Also, is the new battery the same chemistry and capacity as the factory one? Did you reset the BMS when installing?

 

Probably need a new starter.

 

I keep a cheap volt meter plugged in to the power port inside the cubby in front of the console so I can monitor the voltage. It may or may not be perfectly accurate but it gives a good indication of what the charging system is doing. The voltage will vary from 12.8v to 15v depending on the state of charge and condition of the battery.
If your battery is new and fully charged, and the BMS is functioning properly the 13.25v would be inline with what I see on mine so I think your alternator is good. I would think your slow/no start problem is somewhere else.
Bad or corroded battery connections or bad starter.

 

Thanks all, I should have explained that when truck wont start, it does try to turnover, almost seems like "vapor lock" on old cars 40yrs ago
- Newbie, digital multimeter shows charging V l3.25 consistently, V drops initially under load and compensates quickly
- Gus, I'll check the videos.. is this the ground?
- KBroderick, not add-ons. has stock tow package, wondering if this has beefier alternator. New interstate batt is same specs as stock. I did not reset BMS, I guess I need to figure that out
- 52Merc, Tvanpool, I thought about starter and wear due to autostop/start, but don't understand why it would just occur on short trips... wife tends to have everything on when she starts, so assumed battery wasn't recharging for some reason, but new batt should still hack it

 

When I installed a new OEM copy H7 with engine off last October it read 13.05V and 14.70 running new. My OEM battery was showing 'signs' with engine off @ 12.05V which is about 50%. It would recharge itself with a good interstate 50 mile run to about 12.6V then drop after 24 hrs to 12.05V. The engine would start but with winter coming I replaced it (5yrs 2 months old). I firgured it was time. All checked with a good DMM.

 

Not the ground. It might be the sense wire to the PCM. He’s using the PID section of Forscan light

 

How are you measuring 13.25 at the battery? Your own meter? It's possible the meter is slightly skewed.

If the alternator is putting out exactly 13.5 then it may be operating in default, error, mode. If there is a comm issue between the PCM and alternator then the alternator will self-excite when RPM exceeds approximately 2000RPM and then maintain a set 13.5 charge voltage as a fail-safe mode. Normally, the PCM commands the alternator voltage and it will vary based on factors.

If there is an error with comm between the PCM and alternator then you should see a Check/Service Charging System along with a trouble code. The trouble code is not engine/emission related, so it may not turn on the check engine light or the code be readable without an advanced scan tool.