GMT-800: Intermittent "Battery Not Charging" only while towing?

[Martinjmpr]

Anyone else get intermittent "battery not charging" DIC (Driver Information Center on the dashboard) messages and an alternator light lighting up only while towing?

I've had that happen on my last two trips.

Full specs:

Vehicle: 2004 Suburban 1500, 5.3, 4x4, 3.73 rear end with a brand new transmission (though this happened before the trans failed too.)
Main (starter) battery is a Deka 55ah Group 34/78 AGM that I bought new in 2015 right after I bought the truck. It has been run down to the point of needing a jump start at least twice.

Second (house) battery installed in 2016, X2 G34/78 AGM, running through an isolator and primarily used to run the fridge.

Alternator replaced with a rebuilt GM unit in 2017 after failing while on a camping trip.

Trailer: 2018 R-Pod 179 Hood River Edition
2 x 6v Duracell FLA (Wet) golf cart batteries, 230ah each, hooked up in series. (however this also happened with the previous battery set up which was 2 x 12v Interstate deep cycle RV/marine batteries hooked up in parallel.)
Dometic 3-way fridge (120vAC/12vDC/Propane), runs on 12v while we are towing.

So what happens is we'll be driving along and the alternator light will light up and the "battery not charging" warning will come on the DIC. It will stay that way for, at most, 5 or 10 seconds and then go off. This will often happen 5 or 10 times in a row and then will stop for an hour or more, then start again.

A few data points I think are significant:

1. This ONLY happens when towing.
2. It seems to happen during warmer weather more often (though it happened on our way to Texas in November when it was quite chilly, but it didn't happen very much.)
3. I have a Scangauge II and can monitor the charge that the ECU is seeing, and that never varies from the normal charge of ~14.5v - 15.1v. There seems to be no relationship between the charge showing on the Scangauge and the warning light.
4. The light/warning are never on for more than a few seconds at a time.

So I have a theory and I want to run it by the group here since many of you are more knowledgeable about electrical stuff than me:

It is well known in the RV community that the 3 way fridge is a terrible power hog when running on 12v. It is an absorption fridge but like any refrigerator, it runs on a thermostat.

I think what happens is that when the fridge warms up, it tries to "pull" extra power from the battery, which in turn tries to pull it from the alternator which is what sets off the "battery not charging" warning.

I'm going to test this theory next time I tow, by either not running the fridge while towing, or running it on propane. If I can tow under the same circumstances without the warning coming on, that will tell me that it is the fridge on the trailer that is the cause of the warning.

If that doesn't fix it, my next step would be to have the alternator tested, and finally the battery. I have been told my battery is getting old and I should consider a replacement, but I don't want to just throw parts (and money) at this without finding out the actual cause. So far, it hasn't actually caused any problems - my battery holds a charge just fine and the fridge stays cold. But I don't want to get deep into the boondocks and have my battery crap out due to a failing alternator.

I can't remember if the alternator I bought was new or rebuilt. They did have a CORE charge but for some reason I think the one I bought was new. Still, it's seen a lot of hard use in the 2 years since I installed it and just because it was new in 2017 doesn't mean it can't fail.

But I'd appreciate any insight as to whether I'm on the right track.

 

[lilkia]

I think you answered your own question. Your pulling more amps than your alternator can supply. If everything on your trailer is hooked to your 7 pin 12volt its too much.

 

[Martinjmpr]

Currently has a 145a alternator, which I think was the biggest one available in 2004.

Dumb question maybe but other than the initial cost (looks to be ~$300 or so) is there any downside to a bigger alternator? I found one that was 250a.

 

[lilkia]

Other than cost? No downside. An alternator only provides the amperage the vehicle pulls. So if you get the 250 amp alt but your burb only pulls 120 amps without the camper then the alt will only provide 120 amps.
Most vehicles only come with an alternator sized for what they need from the factory with some (large trucks and suvs) having slightly oversized alts. Youve added an aux battery to your rig, a bunch of lights, plus youve got the camper batteries and the fridge. Youre killing youre alternator. Regardless of the aux battery and isolator the fridge is actually running off of the alt when the engine is running. When the vehicle is off the battery supplies the power and draws it down, when the vehicle is running the battery is providing power, but the power drop starts pulling amperage from tha alternator. Consider the battery like a vacuum canister. As the battery develops a power vacuum it has to fill the void and sucks the power from the alt.
Plus if youre running that fridge of the burb power you may want to check your 12v hot wire on your 7 pin to make sure its big enough. Thats another amp killer undersized wiring can cause issues as well.

 

[rayra]

There are three 'factory' alternator amp ratings. I want to say the 'Z-71' / tow-equipped usually have the highest-rated as factory equipment, but I'm not certain. 105A, 130A, 145A

It could be the internal regulator on the alternator, but you should see any issue like that reflected in your scangauge reading too.


IIRC the hot on the 7-pin is fused at 15A. Maybe 20A. You literally can't draw enough thru it to out-draw your alternator output. Not clear from your post if the fridge is in the trailer when towing and powered thru the 7-pin connector? Or is there a fridge in the vehicle AND a fridge in the trailer, both drawing while towing?

Too many variables to say, about the DIC. What's your voltmeter saying when the DIC is sounding the warning? Your scan tool is presumably getting a direct feed from the battery? The voltmeter is in the cluster and if it's a wiring or ground fault related to or internal to your cluster, you might be getting a false error message and it might also be reflected by your voltmeter showing low. If you get a DIC warning and the voltmeter drops BUT your scan gauge says battery volt is still good, then I'd say fault is in the cluster or its ground(s). But it's a mess in there, 14? leads. I've been chasing voltage drain for a good while that ultimately seemed to resolve as my (our) defunct analog OnStar being triggered and uselessly trying to 'phone home'. Pulling battery power and resetting the whole damned vehicle computer setup seemed to resolve the drain. Until the next time I hit something hard enough to trigger the OnStar. No way to shut it down without killing the vehicle speaker amp.

 

[rayra]

Here's your answer. It's 'normal'. Sounds like a lag in the vehicle's charging output whenever there's a ste-up in demand, as in when a fridge cycles on.


https://www.2carpros.com/questions/chevrolet-tahoe-2002-chevy-tahoe--12

Service Information 2002 Chevrolet Tahoe - 4WD | Avalanche, Escalade, Suburban, Tahoe, Yukon (VIN C/K) Service Manual | Document ID: 2170220

#02-06-03-008D: Low Voltage Display on IP Gauge, Lights Dim at Stop Lights, Battery Discharged, No Start, Slow Cranking, Dim Lights at Ilde, Low Generator Output - (Jul 21, 2008)

Subject: Low Voltage Display on IP Gauge, Lights Dim at Stop Lights, Battery Discharged, No Start, Slow Cranking, Dim Lights at Idle, Low Generator Output

Models: 1990-2009 GM Passenger Cars and Light Duty Trucks (including Saturn)

2003-2009 HUMMER H2, H3

2005-2009 Saab 9-7X

This bulletin is being revised to add the 2009 model year. Please discard Corporate Bulletin Number 02-06-03-008C (Section 06 -- Engine).

Any vehicle may have a low voltage display (if equipped with gauges), lights that dim at stop lights, slow cranking, no start, low generator output at idle or dim lights at idle when electrical loads are heavy at idle or under slow driving or infrequent usage conditions. These characteristics may be more noticeable with customer added electrical accessories, or with a discharged battery. These are normal operating characteristics of a vehicle electrical system and no repairs should be attempted unless a proven fault has been diagnosed. ....

 

[Martinjmpr]

There are three 'factory' alternator amp ratings. I want to say the 'Z-71' / tow-equipped usually have the highest-rated as factory equipment, but I'm not certain. 105A, 130A, 145A

Mine came with the factory tow package which includes the 145a alternator. When my alternator died in 2017 I replaced it with what I'm pretty sure was a new (not remanufactured or rebuilt) alternator from Auto Zone as the difference in price between reman'd and new was not enough to justify the cheaper one. The one I replaced it with was also 145a.

It could be the internal regulator on the alternator, but you should see any issue like that reflected in your scangauge reading too.

IIRC the hot on the 7-pin is fused at 15A. Maybe 20A. You literally can't draw enough thru it to out-draw your alternator output. Not clear from your post if the fridge is in the trailer when towing and powered thru the 7-pin connector? Or is there a fridge in the vehicle AND a fridge in the trailer, both drawing while towing?

So there is a 12v fridge in the truck that is running off of the house battery (connected through an isolator to the starter battery.) There is also a 3 way fridge (12vDC/120vAC/Propane) refrigerator in the camper. We normally only run it on 12v while towing, for safety reasons (though I know there are lots of people who tow while running the fridge on propane.) It is a notorious power hot when running on 12vDC.

Too many variables to say, about the DIC. What's your voltmeter saying when the DIC is sounding the warning? Your scan tool is presumably getting a direct feed from the battery? The voltmeter is in the cluster and if it's a wiring or ground fault related to or internal to your cluster, you might be getting a false error message and it might also be reflected by your voltmeter showing low.

The voltmeter on the dash holds steady around 14 - 14.5 all the time. Ditto for the scangauge output, it stays pretty constant. I have not been able to reproduce the problem when parked, it only happens when driving and the "battery not charging" message and battery warning light literally only stay lit for 5 - 10 seconds and then go off again. This usually happens 5 or 6 times in a row and then stops. Then, anywhere between 15 minutes and 2 hours later, it does it again. Engine speed doesn't seem to make a difference, I have seen it happen when I am climbing a grade in 2nd gear at 4000 RPM and also when I am just loping along on flat ground at 2200.

I may just go ahead and get the 250a alternator anyway. With as much power as I'm using, I think more is better. I'll probably wrap the old alternator up in plastic and keep it in my "emergency box" just in case the replacement fails.

I'm not much of a "mechanic" but replacing an alternator on a Chevy is about half a step above "oil change" on the difficulty scale. And the cleanup is easier (my description of an oil change: 10 minutes of prep, 5 minutes of actual work, followed by an hour of clean up!)

 

[rayra]

With two 12v fridges you might be having a condition where they are switching on and off on different cycles and you only get the shortage of amps problem when those cycles get in synch. That could give you the seeming randomness. And that timing synch could be changing all the time, depending on access of the fridges.
Keep in mind that you don't get the the full rated output from the alternator at idle, too

 

[lilkia]

Youre expecting way too much from a 145amp alternator. Your warning signals arent normal with that kind of usage. All of those batteries, two refrigerators and god knows what else. Buy the 250 amp alt. Its like any other tool or machine. If you keep running at its limits its going to fail, and it will fail at the worst time. Having a larger capacity alternator will not hurt anything. If you dont draw the amps it wont produce the amps. It is literally impossible for it to damage your electronics..

I would like to see the hp drain from the two. A 145 amp maxed out vs a 250 amp running at 60%.

Another option is to throw your cold stuff in a cooler while towing and then fire up the fridges when you get where your going.

 

[vargsmetal]

This all sounds like the DIC is false reporting. If scanguage is saying the batt voltage is around 14.5V there is no reason to believe the battery is not charging. A bigger alternator won't solve anything because the regulator is pcm controlled based on voltage alone. If there is no voltage drop the pcm will not up the output of the alternator.

Does your truck have the hall effect current sensor on the battery ground cable?

Take a look at the connections on your alternator, particularly the 4 pin connector.

As long as you're having no issues maintaining 14+ volts at your batteries I wouldn't replace anything. If the wiring is good but the DIC dinging away is a nuisance you can probably have it tuned out.

Sent from my SM-G965U using Tapatalk

 

[luthj]

I think folks here probably haven't had experience with doing the math. A 145 amp alternator is more than enough for the loads described here. I run a 200 amp alternator and I have a 500 amp our bank fridge fan lights etc. And have no issues with over loading.

The fact is that if your alternator voltage is not sagging to below 13.8 V then you're not overloading it. I would be much more likely to suspect faulty wiring to your monitoring module, poor grounds etc.

 

[Martinjmpr]

This all sounds like the DIC is false reporting. If scanguage is saying the batt voltage is around 14.5V there is no reason to believe the battery is not charging. A bigger alternator won't solve anything because the regulator is pcm controlled based on voltage alone. If there is no voltage drop the pcm will not up the output of the alternator.

Does your truck have the hall effect current sensor on the battery ground cable?

Take a look at the connections on your alternator, particularly the 4 pin connector.

As long as you're having no issues maintaining 14+ volts at your batteries I wouldn't replace anything. If the wiring is good but the DIC dinging away is a nuisance you can probably have it tuned out.

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Neither the Scangauge nor the dashboard volt meter are showing < 14v at any time, including the 10 - 15 seconds when the "battery not charging" warning is showing on the DIC. I get other "phantom" messages on the DIC as well: "Service 4wd" comes on every now and then (the 4wd system works fine) and "Service Tire monitor" (again, the tire monitors work fine.) I'm thinking that there is just some momentary loss-of-signal or something to the ECU that is prompting the message.

 

[luthj]

Sounds like an intending intermittent CANbus fault to me.

 

[vargsmetal]

Neither the Scangauge nor the dashboard volt meter are showing < 14v at any time, including the 10 - 15 seconds when the "battery not charging" warning is showing on the DIC. I get other "phantom" messages on the DIC as well: "Service 4wd" comes on every now and then (the 4wd system works fine) and "Service Tire monitor" (again, the tire monitors work fine.) I'm thinking that there is just some momentary loss-of-signal or something to the ECU that is prompting the message.

Right. Only it's not the PCM that's creating the fault in my opinion if the charging circuit is working correctly, which it has to be if its holding 14V under load. It's the BCM, or CAN buss error, or the cluster. If it was my truck I would find out how to shut off the DIC warnings. It's all pointless info (especially if it can't be trusted anyway) if you're monitoring scanguage and your normal guages.

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[rayra]

problem is the GMT800 cluster IS the gauges. It's all electronic / stepper motors. There's 14? wires / circuits feedign into the plug into the cluster. And some stuff connected downstream. There's no simple way to shut off the DIC and keep the rest.

I think Martin's just getting a sort of lagging report. A fridge kicks on, amp demand goes up, alternator output control lags momentarily, monitor decides there's a 'brownout' and sends at alert. Meanwhile the batteries are just fine and alternator output adjusts upward as needed / commanded. It could literally happen in the time it takes to scan your gauges and get to the ScanGauge. Now you see it, now you don't. I'm thinking there isn't anything wrong. Just not 'optimum'. The tech article I posted earlier describes the behaviour, very much matches Martin's description of what he's seeing.

But also, quality of the grounds / corrosion is very important to these highly computerized vehicles. The computers are dependent on line voltages. Sensors are analog, not digital. They're sending variances in voltage, not data bits. Bad or degrading grounds skew those voltage readings, and in turn make the computers' responses false. Acting on erroneous inputs. Then the next thing you know HAL9000 is not letting you back into the pod bay, Dave.