Electrical Problem - Round 2

[Musgofasta]

Morning everyone:

 

This morning, with the new alternator and battery, my in-dash volt meter suddenly reads about 16, maybe more. Not sure if this is bad yet or not.

 

The dealer said the alternator is not sending any signals to the truck PCM which results in the flashing battery light in the message center on the instrument display. I can understand this, but if this is true, shouldn't I get no reading on the dash volt-meter? Or is this meter registrering from somewhere else in the electrical system? I had to order a replacement alternator for the new, partially defective one I purchased yesterday.

 

I guess I'm still not completely sold that my new, albeit remanufactured alternator is the sole culprit to my truck's electrical problems. And I'll be very happy when she runs fine with no big flashing red lights on the dash right in front of me.

 

Feel free to read my post yesterday titled "Electrical Problem - Please advise" for some background info on my symptoms and course of action taken.

 

Thanks!

Musgofasta

[AirForceAngler]

Did you get the PCM problem fixed yet? I wouldn't keep guessing until I fixed what I knew was wrong first.

[Musgofasta]

not yet. Truck runs fine around town except for the now high reading on the dash volt meter and the blinking light. Should have replacement alternator later in the week. Fun stuff this is.

[AirForceAngler]

[Team ZR-1]

GM last year came out with a new Alt that outputs about 40 amps more then older one due to all the electronics in cars/trucks of today.

 

The PCM reads voltage from a different source off Alt so the dash gauge would be different.

 

15 volts is OK, it maybe more like 14.7 cold and with other modules on or A/C drop to around 14.5 volts.

 

The one issue with PCM is if voltage goes above about 15.3 then PCM would trip a high voltage DTC but dealer could program PCM to trip at a higher voltage then when using the 110 amp older Alt.

[99-2door]

The 140 amp alternators like Esclades and some Tahoes have doesn't cause a high voltage reading. I don't see why a higher output alternator would. Lot's of campanies sell HO alternators for these trucks and they don't have problems when they are installed.

[Musgofasta]

good to know. The replacement is a stock 105 amp unit. Having the significantly higher rating on the dash still makes me wonder. On startup, it reads at two full notches about the center "14" notch, then comes down to one notch about center after its warmed up. Fresh battery and alternator might be putting out slightly more volts into the system. Should know more tomorrow.

 

I might drop this alternator into my mom's yukon and see if I get the light to come on in the dash. That would seal the deal for a defective alternator.