Powertrain Control Modules will usually shut down below 10 volts for self-protection but that is unlikely the problem this time. Low cranking voltage can disturb electronic throttle control calibration and cause closed throttle engine stalling.
Like I stated it’s my sons car but I checked with him again this morning.
To summarize : Three low speed stalls and immediately started up all three times. Two at low speeds around town, parked it and checked the things I told him ( battery cables, etc. ) to check . A few days later stalled at a stop light on the way to dealer.
He told me again today all three starts the battery/starter sounded normal/ strong.
P.S…everything is fine since new battery replaced the supposedly undersized (i.e. amps) and weak rental company replacement battery.
A vehicle should be able to start at 7.2 Volts. The engine sensors and fuel injectors operate at 5 Volts for this reason. When cranking in cold weather a 12V battery’s Voltage drops down a lot. 800 cranking Amps on the battery sticker means 800 Amps at 7.2 Volts after 30 seconds of cranking. I wonder if the non essential for starting things like oxygen sensors and transmission control need more Voltage to function.
I’ll have to try this out on my car!
No it will not.
They do not operate at 5 volts. Neither do the ignition coils, fuel supply pump, engine management computer, or anti-theft systems. All of which are needed to successfully start and run an engine.
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You forget the SNOWMAN knows it all. 
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When cranking your car at -15F in the winter, your battery certainly isn’t going to be putting out 12 Volts.
A 2017 Kia probably uses an electric-motor operated throttle valve. This is unlike my 90’s Corolla, which just has a cable from the accel pedal to the throttle body actuating lever. The problem with the cable throttle system is that gasoline engines have to be able increase the rpm in certain extra engine-load situations to avoid stalling.
- Turning headlights on, or rear window defroster, both increase alternator load
- Turning the steering wheel increases steering pump load
- Engine compartment fan turning on increases alternator load
And an increase in rpm is required for low engine coolant temperature .
On my Corolla each of those is handled by a separate gadget. On a 2017 Kia, the electric motor that actuates the throttle valve probably handles all of them via instructions from the ECM. In other words the ECM is what prevents idle-stalling. And that algorithm is very complicated, b/c of all the things that can cause stalling. Furthermore, the anti-stall algorithm that worked last year may not work this year, b/c some engine parameter has changed with engine use.
To address all this anti-stall complexity the ECM maintains a list of parameters it knows will keep the engine running. If something in the engine changes, the ECM just updates that parameter. Then the next time the engine is started, it idles good as new. The problem however is that if the battery gets too low, the ECM “forgets” these updated parameters and reverts to the parameters it used when the car was new. I expect that’s the reason for the stalls you were experiencing.
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When you are cranking your car at any temperature your battery is not putting out 12 volts.
A modern era car is not going to start at 7 volts. It won’t even crank over. It might blip 11 something for a few milliseconds but by then the engine is up and running. Might hit 10s if the battery is on shaky ground.
This is kind of an “out there” thought, but does this car have a start/stop function that turns the engine off at stop lights/signs? My Cherokee does and there is a sensor on my battery that kind of lets it know when it can and cannot function. Mine has acted up before (not like you describe; it just stopped working completely) and was finally fixed when the battery itself was replaced. But I suppose it’s possible the sensor on your son’s car thinks the car is stopped at 15mph. If that is the case, replacement of the battery (including the attached sensor) may in fact be the correct repair.
No stop start feature.
A FOLLOW UP on the 2017 Kia Sedona occasionally stalling without notice and immediately starting up afterwards.
Even though the battery had plenty of power to start the car immediately after each stall, it was replaced.
Nothing else was done to the car and the stalling has not occurred since then after many miles and one year.
Lesson learned……with computers and the myriad of sensors on modern cars the slightest voltage / amperage variation from normal can cause gremlins.
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That battery was already living on borrowed time, if it was the original one. I like to replace my batteries proactively, and I begin load testing them when they are 3 years old. Even if it still tests “okay” at the 5-year point, I replace my battery, rather than winding up stranded, or with weird electronic problems.
This was my sons vehicle, bought used, it was a replacement battery of unknown age.
I’m with you I continually load test my batteries and replace by five years.
I didn’t always do this but just thinking of “no start” situations give me anxiety now as an old man. Even though I also carry a jumper pack.