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Old 04-21-2010, 12:45 PM   #1
TLightning
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GM's Tow Haul Mode

Read today that in order to properly charge the battery in a towed RV, the T/H must be on...this boosts the truck system's voltage. If the trailer is too light to use the T/H, turning the headlights on will do the same thing.
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Old 04-21-2010, 01:56 PM   #2
RCN.Stoker
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Can you give the reference? First time I have ever heard this. I only use T/H in hilly terrain.
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Old 04-21-2010, 02:32 PM   #3
bigred715
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Never heard that before. I put it in towhaul mode as soon as I hook up the trailer and it stays that way until I unhook.
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Old 04-21-2010, 02:49 PM   #4
jjackflash
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Quote:
quote:Originally posted by bigred715

Never heard that before. I put it in towhaul mode as soon as I hook up the trailer and it stays that way until I unhook.
Was told to do the same thing by my dealer!
Jack
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Old 04-21-2010, 02:56 PM   #5
TLightning
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Quote:
quote:Originally posted by RCN.Stoker

Can you give the reference? First time I have ever heard this. I only use T/H in hilly terrain.
Sure can, it's in my owner's manual:

"If you are towing a remote (non-vehicle) battery, press the towhaul button located at the end of the shift lever. This will boost the vehicle system voltage and properly charge the battery. If the trailer is too light to use the towhaul mode, you can turn on the headlamps as a second way to boost the vehicle system voltage and charge the battery."
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Old 04-21-2010, 03:46 PM   #6
Clemson1881
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Thanks. Didn't know that, but I always use tow/haul anyway. Good information though.
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Old 04-21-2010, 05:24 PM   #7
bear
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Thanks! did not know that one .

David
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Old 04-22-2010, 11:00 AM   #8
RCN.Stoker
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Gotta read that manual a little closer. Thanks for the information.
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Old 04-22-2010, 11:25 AM   #9
RCN.Stoker
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I just had to do some research on this. http://www.dieselplace.com/forum/sho...&highlight=RVC

Apparently this may not an issue for my Duramax truck. I will do some additional research and see if I can get a definitive answer. I guess if I used a voltmeter and checked for a change in voltage as I switched in and out of T/H that might be an indication.
Fuel consumption goes up with T/H so there is a good reason to pursue further.


Subject: Information on Voltmeter Gauge Fluctuation Due to Regulated Voltage Control System and Concerns About Camper/Trailer Battery Charging #07-06-03-009 - (12/05/2007)



Models: 2005-2008 Cadillac Escalade Models

2005-2008 Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe

2005-2008 GMC Sierra, Sierra Classic, Yukon Models


Voltmeter Fluctuation Condition
Some customers may comment that the voltmeter is fluctuating between 12 and 14 volts on their full size pickup or utility vehicle. Starting with the 2005 model year, light duty full size pickups and utilities are equipped with a new Regulated Voltage Control (RVC) system. This system reduces the targeted output of the generator to 12.6-13.1 volts when in "Fuel Economy Mode" to improve fuel economy. The generator may exit "Fuel Economy Mode" if additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems that usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted.

Camper/Trailer Battery Charging Concerns
Some customers may comment that when towing or hauling a camper/trailer, the auxiliary battery for the camper/trailer will not stay charged. In most cases, this concern is blamed on the new RVC system. While the RVC system does reduce the generator's targeted output voltage to 12.6-13.1 volts when in "Fuel Economy Mode", this feature is bypassed if the tow/haul feature is enabled. With the tow/haul feature enabled, the RVC system will stay in "Charge Mode" and the targeted generator output voltage will be 13.9-15.5 volts, depending on the battery state of charge and the estimated battery temperature. To keep the generator in the "Charge Mode", use either of the following two methods.

The first method is to use the tow/haul mode when towing or hauling a camper or trailer.

The second method is to turn on the headlights, which will increase the generator's targeted output voltage to 13.9-14.5 volts.



GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


Copyright General Motors Corporation. All Rights Reserved.
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Old 04-22-2010, 11:27 AM   #10
randye
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Does anyone know if that is the same for Dodge and Ford or just chevy , GMC?
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Old 04-22-2010, 02:02 PM   #11
RCN.Stoker
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http://64.91.234.154/coppermine/albu...k_Sep_2004.pdf

Unless things have changed since 2005 the Regulated Voltage Control System is apparently not used in trucks with a GVWR greater than 8600lbs. All 2500 and 3500 diesel trucks exceed this GVWR. The manual doesn't say this and the GM Bulletin doesn't specify what they mean by light truck.

Sorry randye I wasn't looking at other makes. Your manual may give you some idea, but as seen in the case of the GM manual it isn't a sure thing.
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Old 04-22-2010, 03:30 PM   #12
TLightning
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I don't place much faith in the 'know it alls' over on the "Diesel Place." My manual does state that charging and being in the T/H mode applys to trucks that have the optional HD wiring harness. It does not apply to trucks with the basic light duty wiring.
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Old 04-22-2010, 05:42 PM   #13
RCN.Stoker
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The reference I gave was from an AC Delco Tech Bulletin. I checked also the GM Tech Bulletins. They say the same thing.
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Old 04-24-2010, 01:29 AM   #14
SlickWillie
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So, I'm thinking if I have a voltage increase in T/H mode, it would be reflected by an increase on the voltage gauge in the cluster. I tried it yesterday; no voltage change. Doesn't really matter, as I always use T/H when towing.
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Old 04-24-2010, 05:32 AM   #15
KathyandDave
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Out on a limb here - I read somewhere that all of our pickups, regardless of marketing terms "Heavy Duty", "Super Duty", etc., are light duty vehicles. Medium duty would be a GMC Kodiak (I think), Ram 5500's (I think I've seen these used by our municipal works department). Heavy duty are the OTR tractors (Volvo, Kenworth, Petes, et.)
I'm interested in the electrical question because I switch off T/H to save fuel on the flats.
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Old 04-24-2010, 08:48 AM   #16
billhoover
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Quote:
quote:Originally posted by KathyandDave

Out on a limb here - I read somewhere that all of our pickups, regardless of marketing terms "Heavy Duty", "Super Duty", etc., are light duty vehicles. Medium duty would be a GMC Kodiak (I think), Ram 5500's (I think I've seen these used by our municipal works department). Heavy duty are the OTR tractors (Volvo, Kenworth, Petes, et.)
I'm interested in the electrical question because I switch off T/H to save fuel on the flats.
I agree and think you are correct. The problem is the manufacturers themselves. My owner's manual talks about 'heavy duty' this and 'heavy duty' that...which refers to the pickups that are all within the "light duty" overall category when looking at the big picture.
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Old 04-25-2010, 10:56 AM   #17
RCN.Stoker
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My 2008 GM diesel dos not have a Regulated Voltage Control system. I looked for the telltale module on the negative battery cable. It isn't there on either battery. This confirms what I have read and been told by others. One last very recent reference:
http://www.motor.com/article.asp?article_ID=1606
I feel safe driving without T/H or the headlights on.
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Old 04-25-2010, 05:23 PM   #18
Clyde n Deb
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Class 1 6,000 Light-duty Light Duty
Class 2 6,001 10,000 Light-duty Light Duty
Class 3 10,001 14,000 Medium-duty Light Duty
Class 4 14,001 16,000 Medium-duty Medium Duty
Class 5 16,001 19,500 Medium-duty Medium Duty
Class 6 19,501 26,000 Light-heavy Medium Duty
Class 7 26,001 33,000 Heavy-heavy Heavy Duty
Class 8 33,001 Heavy-heavy Heavy Duty
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Old 04-27-2010, 03:54 AM   #19
Tom S.
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Quote:
quote:Originally posted by SlickWillie

So, I'm thinking if I have a voltage increase in T/H mode, it would be reflected by an increase on the voltage gauge in the cluster. I tried it yesterday; no voltage change. Doesn't really matter, as I always use T/H when towing.
I don't think it would show up. The gauge is a voltmeter that monitors the voltage in the system, but the increase being discussed would be in amperage, which is not reflected by the voltmeter. Where it might show up is on the tach. If an electrical load is added to the alternator(s) some times an engine will bog down momentarily, but only for a brief period, maybe a second or less. The tach may or may not pick that up - I don't know.
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Old 04-27-2010, 10:28 AM   #20
SlickWillie
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Quote:
quote:Originally posted by Tom S.

Quote:
quote:Originally posted by SlickWillie

So, I'm thinking if I have a voltage increase in T/H mode, it would be reflected by an increase on the voltage gauge in the cluster. I tried it yesterday; no voltage change. Doesn't really matter, as I always use T/H when towing.
I don't think it would show up. The gauge is a voltmeter that monitors the voltage in the system, but the increase being discussed would be in amperage, which is not reflected by the voltmeter. Where it might show up is on the tach. If an electrical load is added to the alternator(s) some times an engine will bog down momentarily, but only for a brief period, maybe a second or less. The tach may or may not pick that up - I don't know.
Quote:
quote:[i]Originally posted by TLightning
Sure can, it's in my owner's manual:

"If you are towing a remote (non-vehicle) battery, press the towhaul button located at the end of the shift lever. This will boost the vehicle system voltage and properly charge the battery. If the trailer is too light to use the towhaul mode, you can turn on the headlamps as a second way to boost the vehicle system voltage and charge the battery."
I suppose I need to read it myself, but from the post TLightning made, looks like we are talking voltage here. I believe the volt meter will show increases instantly, unlike some of the instrumentation which is dampered.
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