Externally regulated HOA on PCM controlled vehicle

[THEMERQ]

I have had a Brand X electrical 270 amp alternator installed on my 2015 2.5L mazda 3 and at times my voltage is dropping to low 12s and sometimes 11.5 while cruising at highway speed. I am running about ~2000 rms on the stock battery and have all 1/0 OFC throughout including a ground from the alternator case to the negative terminal on the battery. I spoke with Brand X and they suggested I turn on some extra accessories like the defroster or a/c to see if it makes a difference and I am still getting the same results. I think the PCM thinks it can only provide up to the stock amount of amperage. The stock alt is nominally rated at 100 amps and the service manual states it can only put out 70% of that when hot.

 

I did a load test on the high output alt a while in park and revving the engine with all accessories on and a 40Hz test tone playing and I clamped 120 amp coming out of the alternator charge wire but voltage was still low 12s. Voltage normally starts at 14 when cold and drops to 13.3 to 13.8 depending on how hot it is. In terms of voltage across the system I am only getting a 0.1 Volt drop from the battery to the amps.

 

I could go with an external regulator to maintain a constant higher voltage but it would reduce the life of the alternator and give me a battery light on the dash. The light might cause me to fail emission testing so I am unsure if I want to go that route. 

 

Is there a way to wire an external regulator to the alt without having a DTC light on the dash? I saw Mike Singer did some kind of mod for steve meade but I tried searching to see if he offered these for other people and didn't find anything.