Question on Dash voltage reading vs OBDII reading

mikeyk101 · January 29, 2023

I had plugged in my OBDII reader as I was checking on another possible issue. I have had this happen before where the voltage gauge seems to be reading high and will stay right in the middle of the hashmark in center marked 14 and the next hashmark to the right of it. I also have an adapter plugged into the dash cigarette outlet that has 3 USB ports, a power port, and a digital voltage gauge. When the dash gauge is showing the higher voltage output, this digital gauge plugged into cigarette lighter outlet will show a voltage if 15.3 volts. It's not the first time this has read that high and does it frequently in much colder weather.

As I mentioned, today, I had plugged in my OBDII reader but noticed that this was showing between 14.1-14.2 volts at same time as higher reading. On return trip after about 20 miles on expressway, the dash voltage reading dropped almost to center hashmark and the cigarette outlet digital gauge was showing 14.6 volts. The OBD reader was showing 13.5 volts.

I'm aware that the alternator out put is controlled and will drop when it needs to. But the different readings are a bit concerning. So which one should I trust? Dash voltage or OBD voltage?

I just want to add that my truck sometimes sits for several days before being driven but has a longish 100+ mile trip most Fridays and again on Sundays.

discgolf01 · January 30, 2023

Got a multimeter? Put that on there and see which one is correct? If you don't my guess is ODBII

mikeyk101 · January 30, 2023

1 hour ago, discgolf01 said:

Got a multimeter? Put that on there and see which one is correct? If you don't my guess is ODBII

Doh! Yes I have one and didn't even think to try that. I'll give that a check on my next trip...

newdude · January 30, 2023

OBD would be reading from live data from the ECM. This would be live and current data.

The gauge is a just a representation with some leeway in it.

mikeyk101 · January 30, 2023

2 hours ago, newdude said:

OBD would be reading from live data from the ECM. This would be live and current data.

The gauge is a just a representation with some leeway in it.

I'm just surprised that it's about a 1.1 volt difference. I was always a bit concerned when I was seeing that 15+ volts on my little extra digital gauge but now I know I don't have to worry about it. Thanks

mikeyk101 · February 14, 2023

So one of the reasons I had been checking the dash gauge and OBDII voltage readings was because we had an extreme cold snap end of January and on the coldest day, I went to remote start and it didn't turn on. I had to go outside to manually start and I got 1 click from starter and that was it. I ended up slapping a battery charger on and let it go for rest of day and overnight. Next day it seemed to start just fine. I hooked up my battery tester to see what condition the battery was in and it showed it was only at about 62% health and had just under 600cca. It should have been well above this and I suspect that this would explain the higher than average voltage charging I was seeing. It seemed to be charging at a higher rate for some time now and rarely would drop down to the 14 on the dash gauge. I don't remember how far back it started doing this but had noticed it going on.

I finally had some time to pull out this battery today for a warranty exchange. (It went a lot quicker after I found the YouTube showing how to do it without needing to remove the coolant tank like I did the last time.) I had bought this Interstate battery late 2021 at Costco so brought it back there for an exchange. I asked about warranty on the new exchange and found out it would be covered for another 36 months just like the one I exchanged! Great!

So I installed the new battery after getting home and checked it with my battery tester. It showed a health if 100% and over 1000 cranking amps. I started the truck and the OBDII showed charging at 13.2v and dash gauge was just a bit to right of the 14 mark. Looks like the battery was the culprit in the charging. I'm just very surprised that I only got just a little over a year with the battery.

swathdiver · February 14, 2023

Mike, you discovered that your charging system was working perfectly and it was keeping that defective battery going for as long as it could. GMs standard for replacement is 64%, if the battery state of charge will not exceed 64% then it's time to go.

I swore off Interstate Batteries decades ago, they just never seemed to last for us but others have had great success. I got 48 and 68 months out of ACDelco 30 month batteries and am now running their ones with a higher reserve capacity.

If you have a good scan tool, you can see what the computer sees in the Body Control Module as regards to battery health, the state of charge, start up state of charge, temperature, voltages, etc. Good way to get ahead of a failing battery.

There are times when we don't drive one of the trucks much and now we put it on a tender to keep it charged up and to de-sulfate the battery which reconditions it.

mikeyk101 · February 14, 2023

1 hour ago, swathdiver said:

Mike, you discovered that your charging system was working perfectly and it was keeping that defective battery going for as long as it could. GMs standard for replacement is 64%, if the battery state of charge will not exceed 64% then it's time to go.

That's good advice. And I have to agree about ACDelco. I found out the hard way when I was doing my brakes and tried going the O'Reilly Auto way and had nothing but problems. I finally gave up and got the ACDelco ones and it solved the issue.

My original factory battery had almost 6 years on it when I replaced it. It still had life and but didn't check it with a tester. I just figured at that age, I didn't want any problems as winter was close. And I'm not too thrilled about only getting just over a year on the Interstate replacement but I will give them just one more try. If this one gives out in same amount of time, an AC Delco will be replacing it.

swathdiver · February 14, 2023

12 hours ago, mikeyk101 said:

That's good advice. And I have to agree about ACDelco. I found out the hard way when I was doing my brakes and tried going the O'Reilly Auto way and had nothing but problems.

Funny you say that, I had a young man trying to replace his drum brakes on my driveway with O'Reilly parts and they were incomplete. The GM brakes include the parking brake lever attached to the shoe where the parts store's shoe, you had to remove and replace the rivet to swap the original over. Added quite a bit of time to the repair.

mikeyk101 · February 14, 2023

In my case, I was working on the fronts. I found an excellent deal on AC Delco rotors on Amazon but then tried to cheapen out with O'Reilly brake pads. They were just a tad too wide and were hard to pop in to the caliper brackets. I had to force them into them. This caused them to hang up at the ears and drag on the rotors. I took them back and exchanged them for another set. They were a little better but I still got dragging. I thought maybe it was the caliper brackets so I bought reman ones and same problem. I bit the bullet and bought a set of AC Delco pads and they immediately fit like they were supposed to and problem solved. I had seen where others just ground off a little metal on the side of the ears but wasn't thrilled about trying that. So the moral of the story is to buy strictly AC Delco parts for the repairs...

mikeyk101 · February 15, 2023

Well although I didn't mention it at the beginning of thread, one of the other reasons besides the not start issue, I have received several On Star alerts and just received another one today. The alerts are

"Proactive Alert: Battery Charge issue on your 2016 Silverado - Run Vehicle. See email for info.

Text STOP to Cancel. (Service Code SAC003.)"

I received first one on Feb 1st, Feb 8th, and again today. All 1 week apart. Hooked up my battery analyzer and it still showed 100% and was at upper 900 cranking amps. But the voltage was down to 12.2v. I did a load test and it passed just fine as well as the start up test.

This time I decided to use my multimeter at the battery as @discgolf01had suggested. With truck running after a couple minutes, the dash gauge was showing a high charge again as well as the USB/digital gauge plugged in to the dash cigarette power port. After running for a couple minutes, the digital gauge was showing 15.1v again. Using the multimeter at the battery, it also showed it charging at 15.13v??? So it looks like it's the OBDII not reporting the actual charging but showing it at about 1v less than actual.

Not sure whats going on. I will say that I haven't driven it since installing new battery 2 nights ago but a new battery shouldn't be normally discharging as much as I found. I'm guessing that there is some kind of parasitic draw that is dropping the battery down and then it charges at such a high rate to recover. I only have 2 possibilities. I do have a dash cam and that has seemed to be acting up since around the extreme cold winter days during January. But I can't imagine this small piece of electronics shouldn't be causing much of a draw down of the battery. The other is an Airlift compressor for the rear air bags but it only becomes active if I check the psi on the remote. After truck was turned off and sat for about 15 minutes, the multimeter was showing 12.47v.

diyer2 · February 15, 2023

IMO

If it won't hold 12.5 volts, new battery. Just went through this with our 19 Hyundai Santa Fe.

I always put a full charge on a new battery with a charger.

Edited February 15, 2023 by diyer2

mikeyk101 · February 15, 2023

1 hour ago, diyer2 said:

IMO

If it won't hold 12.5 volts, new battery. Just went through this with our 19 Hyundai Santa Fe.

I always put a full charge on a new battery with a charger.

Ok, since it is a brand new battery, I will toss my charger on it and see what happens. 2 days ago when it was installed, it had 12.89v IIRC.