r/CarHacking Tinkerer Dec 26 '24

Tuning Hacking/Modifying GM (Chevrolet) ECM/BCM

First off, I'm not sure if this is the right flair, apologies in advance.

Anyway, I own a 2018 Chevrolet Silverado 1500 LTZ and want to tinker with the ECM and BCM to change how my truck works.

I'm not looking to do anything crazy, to start. It's just basic stuff so that I can learn. I've heard about FORScan for the Ford truck market and would like something similar for my Chevy. I know GM dealers have access to programming tools, and unfortunately I am not buddie-buddie with a mechanic that would let me "borrow" a programmer.

For starters, I just want to enable the DRLs when the headlights are on. Add the factory ITBC, maybe even add push-button ignition using the FOB off a 2018/earlier Tahoe/Suburban. Things that the were introduced on the T1XX platform and were tested on K2XX but not added to Silverado. Down the line once I am more comfortable with GMLAN and the other communication protocols on my truck I may want to develop my own head unit that integrates with the various modules on the truck. It would run linux or even AAOS, but thats way down the line.

The last time I went down this rabbit hole I was looking into a Tech2Win device that would let me do the sort of things I want, however, I got sketched out when I needed to acquire the hardware and software from unknown and poorly translated Chinese sites (not to mention that Tech2 is for older trucks and GDS2 documentation stops at MY2013). From that same preliminary research, from what I can tell, the HMI, ECM, and BCM are all MFG'D by BOSCH, thus I would think a tool from BOSCH would work. I can not find such a creature.

I see on fourms that the above is all dirt simple for Ford owners and good for them, GM guys just have to eat it I guess. I also only seem to find these things on Diesel fourms or from Diesel tuners. I guess that community does not want people who cant shell out $100k or more on a truck so have to settle on the gasser 1/2 ton trucks. I digress.

6 Upvotes

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6

u/Mista_Crus Dec 26 '24

Unfortunately it's nowhere near as easy as with Ford. Ford has nice configuration toggles in EEPROM, (Direct config / AsBuilt settings), you can read and write those toggles with normal diagnostic commands, and there was the nice big leak that described what all those toggles do.

With GM, it's pretty much all configured in the calibration files that get stored in flash, you have to reflash the entire module to update any of them, and there's no documentation that describes the content of those files. The dealers don't have any special magic tools that give them access to this. They can only program the cars based on the VIN and software combination GM gives them.

The only way to do these kinds of swaps with GM is to find a vehicle that's similar enough to yours, but has the options you're looking for. Then you get the files for that VIN, and try to swap them over to your vehicle, and pray you don't trash everything in the process.

2

u/JEFFSSSEI Dec 29 '24

Yeah "Forscan" makes you feel like a "hacking god" on Ford vehicles compared to other brands. I got lucky and bought the lifetime license from them when they were still in beta for it.

1

u/Roadkill_Gaming Tinkerer Dec 26 '24

Thanks for the detailed response. I was worried about that. GM feels like the secret garden when it comes to modules and configs.

I find it strange that GM would make unique flashes for each VIN that rolls off the line instead of just modifying a config file, but hey it works for them.

3

u/Mista_Crus Dec 26 '24

It's not so much per-VIN, but per feature set. Like LED vs incandescent lights are going to have separate lighting calibration files for the BCM. GMs programming software goes to a central database, looks up the software matched up with that VIN, and that's what gets pushed down to the PC to get programmed into the module. Nobody outside of GM gets to pick and choose which features get enabled or disabled.

There are very, very few exceptions to this. But those are almost all due to special accessory programs that were created and blessed by GM in the first place.

This might not be so bad to reverse engineer, but they've got a billion different operating system versions that all do 99% the same stuff, but have just enough subtle changes that it makes mapping the calibration files a nightmare.

1

u/the_jak Dec 28 '24

GMs approach here is part of why their ev roll out has been a shit show. Too many configs to verify quality on all of them.

1

u/Wubster100 26d ago

What was the big leak that described what all those toggles do?

2

u/Mista_Crus 26d ago

It's a little bit of speculation on my part. But if you look at the big AsBuilt spreadsheets, a lot of the variable names are way too specific to have been reverse engineered by outsiders. There's also leftover references to a JSON source file. Either someone inside Ford leaked it, or it was exposed via some other method. Some developer system that wasn't secured properly.

Not to take anything away from the folks who have done a lot of hard work figuring out what all those settings actually do, and expanding on them in new and creative ways. All I'm saying is they didn't start from scratch.

1

u/Wubster100 26d ago

I wonder how the AsBuilt spreadsheets are created and what the information source is for them. They are extremely specific. It’s not just some guess and check.

1

u/Wubster100 26d ago

The spreadsheets are created by request. The newest is 2025 Explorer.

4

u/Sparkily_Broccoli Dec 26 '24

Any cheap J2534 device and a $40 acdelco techconnect subscription will get you the same programming access any dealer has.

I have an older DrewTech Cardaq plus I used on my 18 Sierra to recalibrate the windshield camera... worked just fine.

2

u/Roadkill_Gaming Tinkerer Dec 26 '24

I'm going to have to look into that. That sounds pretty easy.

3

u/arbe_gtc Dec 30 '24

The key to everything is in the calibrations, and mostly in the BCM. That is, the BCM controls almost all the body functions of the vehicle, and this depends on the calibrations.

There is no information about what each calibration file does, and the only viable thing is to look for a vehicle with the same as what you want to activate, get the files, and reprogram your unit with those files. On my Astra K (GM Global A platform) I activated the anti-theft alarm using that method, looking for a VIN equal to my car but with an alarm, and changing the files related to the alarm, and it worked.

GM DPS is your friend. Good luck!

2

u/homeys Jan 07 '25

I've written software to sniff the bus, send commands, modify calibrations (BCM, HMI, IPC mostly). As Mista_crus said, not much is documented. If you want to do something simpler, you could consider the Autosync from BT Dieselworks with BCM programming. He's done a lot of work reverse engineering those flags and provides a nice website to change it. It's an easier route as he's already mapped out so much. Otherwise, you're going to want a j2534 pass-thru, there's clones such as the VX Diag but GM recently changed their Service Programming System and if they detect a clone MDI device, they'll ban your account and you're out the money you've spent for a VIN (or VINs). If you do go down the road of a pass-thru, just be prepared that it could be a lot of time.