GMC Truck Thread

[SkiBum5.0]

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Looks like the L5P ECU has been cracked. Insane numbers so far. 600+whp and 1200+ft/lb. Stock engine minus emissions. Tranny is so far holding up (TCU tune as well). The pre-'17 LML guys are going to take a huge hit resale wise as its no longer coveted. The new platform will keep holding its value into the first few years of the next generation.

I've been lurking the duramax forums waiting for this. I'm working on a 3500 SRW deal down here. Was going to start with a Banks Derringer.

[The Cosworth]

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I'm not an expert, but isn't there supposed to be something? Any diesel guys want to chime in? Most diesels have two batteries right?

Don't see why not, figure it is just a capacity thing. You can have one huge battery (like the 24v'ers that Semi's use) but then that truck would need to make sure it had a spot for a big battery, have the dealers stock it, have the assembly line handle it. Or they could just engineer 2 spots and if you need / want 2 you just drop em in.

But, there might be another reason I don't know, that you would want them separate.

Found a couple posts about it, it just sounds like in parallel but 3rd hand.

https://www.duramaxforum.com/forum/g...ery-setup.html
https://www.duramaxforum.com/forum/m...battery-2.html ------ First post. What does each run. Second post. They're in parallel.
https://www.dieselplace.com/forum/63...batteries.html

[ExtraSlow]

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Don't see why not, figure it is just a capacity thing. You can have one huge battery (like the 24v'ers that Semi's use) but then that truck would need to make sure it had a spot for a big battery, have the dealers stock it, have the assembly line handle it. Or they could just engineer 2 spots and if you need / want 2 you just drop em in.

But, there might be another reason I don't know, that you would want them separate.

Found a couple posts about it, it just sounds like in parallel but 3rd hand.

https://www.duramaxforum.com/forum/g...ery-setup.html
https://www.duramaxforum.com/forum/m...battery-2.html ------ First post. What does each run. Second post. They're in parallel.
https://www.dieselplace.com/forum/63...batteries.html

They are for sure not in pure parallel, because they are at very different voltages right now. 13.0 for the aux and 12.3V for the main (passenger)

Since I charged both recently, that doesn't bode well for the health of the main.

[HiTempguy1]

Well you just answered your own question. One of your batteries is toast.

A dead battery will certainly deplete the charge of a 2nd parallel battery very quickly.

I don't think there is any isolation, what would be the point? Dual batteries in diesels are for cold starts where one battery may not be able to sustain cranking the engine over enough times to start.

There isn't some sort of relay that controls this. They are just linked together.

[ExtraSlow]

Yeah, i always thought it was like in a motorhome where one battery woukd run the "house" circuit and have some isolator to prevent you running down the "chassis" battery.

Not that it matters much in my application, as I don't have a camper on this truck, but it bugs me.

I'll be replacing the bad battery.

[ExtraSlow]

Just following up on how it appears the dual batteries in my truck are wired. I have the factory TP2 option on my 2010 Silverado 2500 HD Gas truck. No idea if this is same or different than in diesel trucks or other brands. Found this description on another forum which matches perfectly with the behavior I'm seeing.

There can be alot of confusion because there are a few different ways to wire dual batteries up. There are also options on individual vehicles after the batteries that make a difference. Without knowing exactly what you have (TP2 isn't the only code that makes a difference in how it all works so a vin would help) I can only give some basic answers to your questions.

Does the starting system use both bateries to start the engine?-------No not on your vehicle
do both battries charge at the same time?-------------Yes on your vehicle
If I replace the main battery should I replace the aux. at the same time?------Yes, always in my opinion

Ok well I can do better than basic but this may not be the whole story. The auxillary battery is active anytime the ignition switch is in the run position with TP2, it is not involved in the circuit when the switch is in the crank position. Charging with the alternator only takes place with the vehicle running and switch in the run position so it is going to be charging at the same time as battery 1. That doesn't mean it's charging at the same rate, that depends on battery condition. If one is not as healthy as the other than charge rates are going to vary side to side. That brings us to the last question about replacement, there is debate here, but my suggestion is to maintain system integrity I always replace them at the same time with the same type of battery and I try to make sure the manufacturing date is close on both.

I say this matches the behavior I'm seeing because there's clearly a relay or something between the batteries when the truck is not driving, but both batteries connected, as they sit at very different resting voltages.

EDIT: Found this description on another forum too.

Dmax trucks do not have RPO TP2, which is the auxiliary battery optional on Gas trucks. The Dmax has RPO TQ3, which is a dual battery system so as stated above, the fuse is needed.

[The Cosworth]

Huh, interesting, seems overly complex and not really sure for what benefit.

[ExtraSlow]

Sort of similar but slightly different than how motorhome and campers are wired. I'm not really sure of the point, but does mean you can boost yourself in an emergency. So that could be handy.

[SKR]

I have a 2017 3500 of my own and a 2017 2500 for work, and the more time I spend with them the less I like them.

Compared to the previous gen, the interior is fancier with all its buttons and everything but I've never really felt like any of it was in a good spot. Seems like everything I need is just out of reach. In both trucks, 20 degrees is polar cold and 21 is the core of the sun, so I constantly have to adjust the temperature. I don't like the carpeted wheel wells. They're impossible to get clean. Those black plastic fender things will never be clean either. I feel like the truck is just going to rust into nothing because of those two things. And then today I was at the car wash and I took out the driver's side Weathertech floormat and pulled one of the tits out of the carpet. I knew those tits would be a problem from day 1, and they don't even need to be there.

The L5P is a better motor than the LML before it, and the electric power steering in my 3500 is nice. That's all I like, I think.

[ExtraSlow]

Wipers had died on my truck. Installed a new wiper motor/linkage part today. What a bitch to get to. Got the correct AC delco part from Amazon for $80 less than dealer.
Probably 45 minutes to take everything apart, and then 10 minutes to actually replace the part.

[403Gemini]

Finally got my posting up in the marketplace for my 2016

Pains me to list it , just been thinking about changing careers lately and would be looking at probably taking a deduction in pay, and now having a 2 year old girl I'm trying to cut back on monthly expenses and my wife likes driving the Ford Edge more than the Sierra. Incredible trucks though, so comfortable to drive . I had an F150 through work for awhile and always preferred the Sierra, just enjoyed the console/interior more and the front end looks more aggressive (least to me, but of course that's personal preference)

This thread was actually the inspiration that got me wanting a Sierra haha

[94boosted]

FFS, this AFM Exhaust Valve is a major PITA and Shaganappi sucks.

Sept. 2017 & ~43K km's
Chirp is noticed when switching from V4 to V8, vehicle is brought in to Shaganappi, they confirm the noise and replace the entire exhaust system with a supposedly "updated" unit that addresses the chirp. Problem solved, or so I thought.

Nov. 2018 & ~61K km's
Chirp is back, I try to book the truck in before my comprehensive warranty lapses (Nov. 17) but they don't have availability until Nov. 20, not a big deal I think. This chirp is an obvious & known issue on these trucks (PIT5404D) and they can't possibly try to force me to pay for a new exhaust 14 months/18K km's after they replaced the last one and 3 days after my comprehensive warranty is up can they..... they sure can plus $200/hr for diagnostic time (something you can literally diagnose on the 50m drive from the parking area to the mechanics bay).


This is the second time I've had a bad experience with Shaganappi service. I've called GM Canada to complain so I'm still hopeful they can do something. If that doesn't work, does anyone have any suggestions? I've heard that if you cut the valve out or bolt it open the truck makes some funky noises when in V4 mode and I'm not really sure about getting any sort of an aftermarket tuner like an inTune to disable AFM and potentially have powertrain warranty issues. I believe that valves default position is open?

[roopi]

2020 Silverado - This can't be real can it???

[Tik-Tok]

I see they're hiring 6 year olds to design the exteriors now.

[ExtraSlow]

I assume in ten years when there's a chance of my owning one, I'll have grown to dislike it less. I pretty much always hate new trucks, and that's been true since the nineties.

[SKR]

I hate what GM's design department is doing oh so much. That 10 speed Allison would have to be unbelievable to make me want to buy one.

Maybe the GMCs won't be so unsettling.

[ShermanEF9]

That front end and the mirrors are hideous.

[CMW403]

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I hate what GM's design department is doing oh so much. That 10 speed Allison would have to be unbelievable to make me want to buy one.

Maybe the GMCs won't be so unsettling.

My father was one of the first in the city to receive a fully loaded 2019 Denali 1500, that new 6.2L coupled with the 10 speed Allison is remarkable. Trust me.

[ExtraSlow]

Is the 10 speed in the 1500's an allison? I thought it was the Ford/GMC joint venture transmission?

[ShermanEF9]

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Is the 10 speed in the 1500's an allison? I thought it was the Ford/GMC joint venture transmission?

you are correct.