Battery change causes default mode??

03 gmc 2500HD4x4 LB7 bought used 1 yr ago
Had a no start today, 5 degrees out and windchill of -15. truck was plugged in for about an hour, but batteries did not have enough juice.
here is the problem
Put 2 new matching batteries in, started out to return the cores and could not get more than 2000rpm and check engine came on. Dropped the cores off and on the way home power returned ran like always, but still have a light.
can't get it scanned till mon, to see what is stored.
has anyone heard of a problem when disconnecting both batteries at the same time with it going into default and setting a light?

I have replaced a few batteries on the DMAX, but never had your problem. Just for grins, disconnect both batteries for 1/2 hour, reconnect and try again. This is not a fix, but may clear the dtc's since you do not have a scanner available to you.

Just had it out again, light cleared itself. I'll have it scanned Mon and see if it set a code. definitely scratching the head on this one:confused:

Finally got a chance to post codes:confused: too many

P0087A fuel rail pressure low (twice)
P0404 EGR open pintle
P0650 MIL control circuit
P0700 TCM MIL request
U1041 ??
P1093C Fuel rail pressure out of range
U1152 ??

This is the order they were in, would the fuel rail fault be the reason for the default? Don't know why it happened with the battery change

planning on doing a service to it and changing the fuel filter.

any ideas?

Purely timing and coincidence...

Change fuel filter, reset codes, repeat every ~15K miles.

Thankyou, I've had just a year and never checked for codes,some may have been there when I bought it! I've put only @5000mi on it, it was supposedly gm certified when i bought it

Make sure you clear the codes - after changing the filter.

OOPs maybe cleared the codes when we read it the other day. Not a problem I have acess to the scanner so i'll check after the filter change, just too cold here right now to mess with it

I just replaced both of my batteries last night on my '03 GMC (original Delco's went 6+ years!!). One of the old bats (right side) had a dead cell, so when I pulled the left side bat, there wasn't enough juice to run keyless and my radio clock reset, even though I was doing one bat at a time to avoid stuff like this. Anyway, I didn't have the problem with the codes that you experienced. My truck was driven to the auto parts place where I did the battery swap in the parking lot. If your truck never started (but cranked slowly) when the old bats were dead, maybe the low voltage caused the codes and it just needed a complete ign. cycle to say 'all is good'?

BTW, I apparently had a dead cell on the right and a lame left battery for a while because I don't remember the motor ever cranking as fast as it does with the 2 new bats!!

Unfortunately, new Delco's were $126 ea and new Autolites were $85. Delco's had a 50 month full replacement (compared to 24 mo for the Autolites) but the Delco's overall warranty (pro-rated portion) was a year or so shorter than the autolite. I couldn't justify 50% more $ for the delco's even given the longer full replacement warranty and that the OEM units lasted so long. Hopefully I won't live to regret this.

What I realized when changing the batteries is, the dealer I bought it from changed only 1 battery and the otehr was original!
Bought 2 NAPA 78 month batteries, cold crank at 0 degrees at 900.
now even my son can not get over how fast it starts