Chevrolet Suburban 3500 Questions

[Bigburb3500]

Off on a tangent... curious from those of you who have gone from a 08-13 2500 (6 Speed) to a 3500, is your towing mileage any different? The 3500 has 4.10s vs 3.73s on the 2500, but with the 2500 towing close to 10K it doesn't spend much time in 6th except going down hills.

So I will not be able to comment much on this in terms of comparison but based on GeoTrash’s experience it’s not mileage you gain but stability and confidence. These trucks are pretty stout, but generally similar/identical frame wise to the GMT900 2500 Subs.
I think you are mainly getting newer tech, bigger brakes, and a fleet designed truck vs a consumer biased vehicle.

 

[TripleFJeff]

So I will not be able to comment much on this in terms of comparison but based on GeoTrash’s experience it’s not mileage you gain but stability and confidence. These trucks are pretty stout, but generally similar/identical frame wise to the GMT900 2500 Subs.
I think you are mainly getting newer tech, bigger brakes, and a fleet designed truck vs a consumer biased vehicle.

I was curious because I've seen lots of different numbers out there for them and they seemed higher than I'd expect, like 16/23 which can't be right. Since it's a 3500 and the EPA doesn't require fuel economy testing on the 3500s you can't look it up on fueleconomy.gov. I wouldn't expect it to be any better than my current one, as the only real difference is 4.10 vs 3.73.

Chassis-wise, I'd expect it to be very similar to my 2500 which is already great. The only reason I'm considering switching is it's getting old (210K) and while it's been great, it's starting to get some small leaks and rust and I'd like to get out of it before anything big happens.

 

[Bigburb3500]

I was curious because I've seen lots of different numbers out there for them and they seemed higher than I'd expect, like 16/23 which can't be right. Since it's a 3500 and the EPA doesn't require fuel economy testing on the 3500s you can't look it up on fueleconomy.gov. I wouldn't expect it to be any better than my current one, as the only real difference is 4.10 vs 3.73.

Chassis-wise, I'd expect it to be very similar to my 2500 which is already great. The only reason I'm considering switching is it's getting old (210K) and while it's been great, it's starting to get some small leaks and rust and I'd like to get out of it before anything big happens.

Around town driving I can attest that my mpg is about 13.5-14.5. Highway cruising at 65MPH you can get into the 16MPG but it will hover around 14.5-15.5 if going above 70MPH.
Towing I have little I can offer as I don’t do much at this point. This is a HD family hauler for me.

 

[Geotrash]

I was curious because I've seen lots of different numbers out there for them and they seemed higher than I'd expect, like 16/23 which can't be right. Since it's a 3500 and the EPA doesn't require fuel economy testing on the 3500s you can't look it up on fueleconomy.gov. I wouldn't expect it to be any better than my current one, as the only real difference is 4.10 vs 3.73.

Chassis-wise, I'd expect it to be very similar to my 2500 which is already great. The only reason I'm considering switching is it's getting old (210K) and while it's been great, it's starting to get some small leaks and rust and I'd like to get out of it before anything big happens.

Like you, I think 16/23 is fantasy. I've seen 20 on a 150 mile highway trip with just me on board.

 

[Marky Dissod]

16 (City MpG) /23 (Highway MpG) is fantasy.

CAFE MpG test scores are not 'normally' achievable by 'normal' people driving 'normally' on flat terrain,
if only because vehicles are tested individually in controlled conditions,
NOT in traffic, which nearly always costs nearly every driver at least 2MpG.
Only way to achieve CAFE MpG test scores is to accelerate mildly, coast more and more often,
and driving slow enough to slow other drivers as well.

To oversimplify / jump ahead, hypermilers often exceed CAFE MpG scores by at least 10%.
They do so by making DRASTIC sacrifices in time-to-destination, chiefly by
coasting as much as physically possible, accelerating glacially,
and planning for avoiding braking as much as possible (think about it).
All too often, they slow traffic aft of them, making others waste their MpGs thru impatience.

 

[Bigburb3500]

CAFE MpG test scores are not 'normally' achievable by 'normal' people driving 'normally' on flat terrain,
if only because vehicles are tested individually in controlled conditions,
NOT in traffic, which nearly always costs nearly every driver at least 2MpG.
Only way to achieve CAFE MpG test scores is to accelerate mildly, coast more and more often,
and driving slow enough to slow other drivers as well.

To oversimplify / jump ahead, hypermilers often exceed CAFE MpG scores by at least 10%.
They do so by making DRASTIC sacrifices in time-to-destination, chiefly by
coasting as much as physically possible, accelerating glacially,
and planning for avoiding braking as much as possible (think about it).
All too often, they slow traffic aft of them, making others waste their MpGs thru impatience.

We use every bit of their 10%… especially when they hyper mile in the passing lane…

 

[Marky Dissod]

We use every bit of their 10% … especially when they hypermile in the passing lane …

My point exactly.
They usually have nearly the same effect on the rest of us as a blocked lane,
meaning that as they seek and achieve diminishing fuel economy returns
(Miles per Gallon is far dumber than Gallons per Mile),
everyone behind them wastes time and gas trying to circumvent them.

Hypermilers are actually one of the reasons why I've little complaint against
6L80, 8L90, and 10L80 developments - they improve city MpG for EVERYONE,
and make hypermilers a bit less of a problem for the rest of us.

 

[TripleFJeff]

CAFE MpG test scores are not 'normally' achievable by 'normal' people driving 'normally' on flat terrain,
if only because vehicles are tested individually in controlled conditions,
NOT in traffic, which nearly always costs nearly every driver at least 2MpG.
Only way to achieve CAFE MpG test scores is to accelerate mildly, coast more and more often,
and driving slow enough to slow other drivers as well.

To oversimplify / jump ahead, hypermilers often exceed CAFE MpG scores by at least 10%.
They do so by making DRASTIC sacrifices in time-to-destination, chiefly by
coasting as much as physically possible, accelerating glacially,
and planning for avoiding braking as much as possible (think about it).
All too often, they slow traffic aft of them, making others waste their MpGs thru impatience.

I'm quite familiar with how the ratings are done, and this is simply not true. The testing is done on a dyno with a test cycle that includes simulated hills and varying speeds. While there are certainly lots of variables and "your mileage may vary", it is very possible to exceed the highway numbers while driving normally and above the posted limits.

My 2008 Suburban 2500 is listed as 12/17. It regularly gets 16-17 on a highway trip through hilly areas (central/western PA) at 75MPH. Our 2020 Mazda CX5 Turbo is rated 22/27, and gets 29-30 on a highway trip at 70-75MPH. 23 for a Suburban with the same engine and transmission but 4.10 gears instead of 3.73 sounds like it is simply a mistake.

 

[Geotrash]

I've been getting a Service Power Steering message every time I start the engine for the past few weeks. It started a couple of weeks after the Denali cluster upgrade, but I don't think it's related since there was a significant time lag between the upgrade and the messages starting. Coincidentally, when I hook up either a GM-specific scanner or a J2534 pass-thru scanner and use the ACDelco service to perform diagnostics, neither can communicate with the Power Steering Module, so something is amiss and it's also keeping me from getting any error codes from the module.

I checked the fuse for it, which is in the fuse block on top of the battery and I have continuity there, so I'm suspecting a wiring problem between the BCM and the steering box.

If one of you happen to have a scanner that can read all of the modules on yours, could I trouble you to check to see if your power steering control module is able to communicate with your tool, or not? I;m trying to figure out whether I have a legitimate problem with the module, or if none of the tools - including GM's own - are confused about the existence of said module.

 

[TripleFJeff]

Are you sure it even has one? If your cluster came from a 1500, it could be a no-comm error because it's not seeing a module it expects to see. Check for codes in the cluster itself to see if there is a no-comm code.

 

[Geotrash]

Are you sure it even has one? If your cluster came from a 1500, it could be a no-comm error because it's not seeing a module it expects to see. Check for codes in the cluster itself to see if there is a no-comm code.

There is. It's a lost communication code but it's for the HUD display, which my cluster has enabled but I do not have the module installed for. And there is also a security code error.

You might be on to something though because the 1500's have electrically assisted power steering, but the 3500 has hydraulically assisted power steering. Still, I can't figure out why the instrument cluster would care about the steering control module. It's been programmed to the VIN as well, but that may not matter.

Unrelated, I believe, but I also had a code that has since reset itself for the fuel pump in the rear tank:

 

[Geotrash]

Here's a little more detail on the errors. One other thing is that because the cluster isn't the one that came with the truck, I can't program/update it with the SPS software because the updates SPS wants to apply are keyed off the VIN. Starting to wonder if the Denali cluster upgrade was worth it. Glad I kept the original, just in case.

Update: I wrote to White Automotive today and they confirmed that the instrument cluster messages are both normal, so I'll quit worrying about them. The Service Power Steering message is continuing to vex me, however.

 

[Bigburb3500]

Here's a little more detail on the errors. One other thing is that because the cluster isn't the one that came with the truck, I can't program/update it with the SPS software because the updates SPS wants to apply are keyed off the VIN. Starting to wonder if the Denali cluster upgrade was worth it. Glad I kept the original, just in case.

Update: I wrote to White Automotive today and they confirmed that the instrument cluster messages are both normal, so I'll quit worrying about them. The Service Power Steering message is continuing to vex me, however.

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It’s more annoying than anything because what happens when you do have a problem?

 

[TripleFJeff]

Assuming that the issue is a no-comm (which jives with the report above), the message is being triggered one of two ways. The first is that the cluster itself is monitoring the presence of the steering module, and reporting the fault when it doesn't see it. The other is that some other module is monitoring it, and when it sees a fault it is sending a message to the cluster to show the fault in the display. The second seems more likely, since the cluster probably doesn't need anything from the steering module so it wouldn't be monitoring it for no-comm.

While your cluster may have been programmed to your VIN for anti-theft, since it's not a valid part for your truck I wouldn't expect that it is configured properly for what parts yours has.

 

[Geotrash]

It’s more annoying than anything because what happens when you do have a problem?

Another good reason to keep the original cluster. If I ever have a problem that requires cluster programming, I can just pop in the original. In the meantime, I really like the functionality in the Denali cluster. The transmission fluid temperature gauge in tow/haul mode is wonderful, for example.

 

[Geotrash]

Assuming that the issue is a no-comm (which jives with the report above), the message is being triggered one of two ways. The first is that the cluster itself is monitoring the presence of the steering module, and reporting the fault when it doesn't see it. The other is that some other module is monitoring it, and when it sees a fault it is sending a message to the cluster to show the fault in the display. The second seems more likely, since the cluster probably doesn't need anything from the steering module so it wouldn't be monitoring it for no-comm.

While your cluster may have been programmed to your VIN for anti-theft, since it's not a valid part for your truck I wouldn't expect that it is configured properly for what parts yours has.

This is what I’m thinking as well. However, I expected the GM software to be able to get the modules right. So, I’m thinking I still have a communication problem on the CANbus with the steering control module.

 

[TripleFJeff]

This is what I’m thinking as well. However, I expected the GM software to be able to get the modules right. So, I’m thinking I still have a communication problem on the CANbus with the steering control module.

The GM software only allows you to program a module for a vehicle that it available on, and you need a VIN to do it. For example, my 2500 originally came with tow mirrors and a prior owner had swapped on non-tow, power fold mirrors mirrors but didn't change the door switch module to one with the power fold button. I swapped the door switch module to one with power fold, but then my driver's side heated seat quit working because the switch came from a truck without heated seats. You can't just change that parameter. I had to go on autotrader and find a truck that had heated seats and power fold mirrors (and matched everything else), and use that VIN to program my switch module. So if that cluster never came on a truck without a steering module, it's impossible to fix.

That said, I'm still 99% confident that your truck does not have a steering module. Have you actually put hands on it? Are there any electrical connectors that go to the steering gear or pump?

 

[Geotrash]

The GM software only allows you to program a module for a vehicle that it available on, and you need a VIN to do it.

Thank you for your continued thoughts. I had this thought as well, yet entering the VIN in the GM software and website still returns that it has a power steering control module. And the cluster was programmed to the VIN as well, by White Automotive. The fly in the proverbial ointment though is that the cluster came from a different year Denali. But given that none of the 3500’s were Denali’s, I don’t know that it would matter. None of them were likely configured with the 3500-specific features.

For example, my 2500 originally came with tow mirrors and a prior owner had swapped on non-tow, power fold mirrors mirrors but didn't change the door switch module to one with the power fold button. I swapped the door switch module to one with power fold, but then my driver's side heated seat quit working because the switch came from a truck without heated seats. You can't just change that parameter. I had to go on autotrader and find a truck that had heated seats and power fold mirrors (and matched everything else), and use that VIN to program my switch module. So if that cluster never came on a truck without a steering module, it's impossible to fix.

I had this thought also. I have programmed many modules to the VIN of my Yukon XL’s using a Tech 2. But like you, I can’t figure out what the cluster would have to do with the power steering control module except to be the receiver of any fault indications. All the same, that the cluster is creating the issue is the most plausible theory I have so far.

That said, I'm still 99% confident that your truck does not have a steering module. Have you actually put hands on it? Are there any electrical connectors that go to the steering gear or pump?

No, but the GM software indicates at least 6 different BCM “modules”, so I’m not sure it would be a physical module. It may occupy a logical space on the BCM’s mainboard or reside in the BCM’s housing. I also looked for electrical connectors and while there are several on the steering column, there appear to be none on the steering pump or steering gearbox. It has the same reciprocating ball setup as the GMT900 2500 platform.

Also, I would think that the Stabilitrak system needs a source of steering data, so unless that’s coming from a different module, I would think it still needs a steering control module of sorts. But again, I have no data on it. Alldata thinks it has a rack and pinion setup, so I don’t trust the schematics. Though they do denote which drawings are applicable to the L96-equipped trucks, of which the 3500 is the only one so equipped.

I’ll ask the guys over at duramax specialties on their Facebook page. They’re really good about helping folks out, even those who don’t have one of their rigs.

 

[Geotrash]

Update: the owner of Duramax Specialties is a great guy and was kind enough to confirm that the 3500 HD Suburbans DO NOT in fact have a Power Steering Control Module. He suggested I get with the White Automotive to have them deal with the error. I'll reach out to them today and see what they say.

 

[1TONSUB]

Add another Suburban 3500 owner to the forum. Will be nice to be in company with some other enthusiasts. Will start thread with details of my build.