Intermittent CEL / P0700 / Battery Tender

Tomato · February 26, 2021

I have been having intermittent CEL issues, and I am now pretty sure it is caused by low voltage at start up. Truck sat for 6-days this time, and the CEL came on at start up - like several times in the past. I shut it down right away and checked the batteries - 11.9 volts. iDash shows only P0700, but I usually get U0100 as well. I think this thing has a significant vampire draw when sitting.

I am going to put it on a trickle charge going forward. Question for those that do this with dual batteries. Are you just connecting to one or the other or using a double charger of some sort?

Thanks.

Njmurvin · February 26, 2021

I haven't used a charger on my Silverado yet. But I used it once on my Ram 3500 which also had dual batteries. I left the ignition on one night and drained the batteries pretty well. Next morning it wouldn't start (surprise!!). I connected the charger to the driver side battery only and in a few hours, the truck started right up.

I would also try to find out where the parasitic drain is. I have left my truck in the garage for at least 2 weeks on multiple occasions and had no problem firing it up.

Edited February 26, 2021 by Njmurvin

redwngr · February 26, 2021

20 hours ago, Tomato said:

I have been having intermittent CEL issues, and I am now pretty sure it is caused by low voltage at start up. Truck sat for 6-days this time, and the CEL came on at start up - like several times in the past. I shut it down right away and checked the batteries - 11.9 volts. iDash shows only P0700, but I usually get U0100 as well. I think this thing has a significant vampire draw when sitting.

I am going to put it on a trickle charge going forward. Question for those that do this with dual batteries. Are you just connecting to one or the other or using a double charger of some sort?

Thanks.

GM does have diagnostics to track down excess draw while shut off. I'd be getting GM to track it down and correct it, as there have been reports of problems resulting in above normal draw.

Should be able to park much longer that 6 days without low battery.

Obviously it shouldn't need a tender for 6 days of parking....

Better to correct the problem than to mask the symptoms.

For charging, the dual batteries are hooked together so they behave like one big one.

Tomato · February 26, 2021

35 minutes ago, redwngr said:

GM does have diagnostics to track down excess draw while shut off. I'd be getting GM to track it down and correct it, as there have been reports of problems resulting in above normal draw.

Should be able to park much longer that 6 days without low battery.

Obviously it shouldn't need a tender for 6 days of parking....

Better to correct the problem than to mask the symptoms.

For charging, the dual batteries are hooked together so they behave like one big one.

Agree. I will have them check next time I am in for service. One other note is that I was in and out of the truck grabbing stuff probably 6-10 times while it sat. As you know, the electronics "fire up" for a short time each time you open the driver's door.