Hacking/Modifying GM (Chevrolet) ECM/BCM

[u/Roadkill_Gaming]

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.

[u/Sparkily_Broccoli]

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.

[u/Roadkill_Gaming → u/Sparkily_Broccoli]

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

[u/Mista_Crus]

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.

[u/Roadkill_Gaming → u/Mista_Crus]

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.

[u/Mista_Crus → u/Roadkill_Gaming]

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.

[u/the_jak → u/Roadkill_Gaming]

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.

[u/JEFFSSSEI → u/Mista_Crus]

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.