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2020 Chevy Bolt LT
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Discussion Starter #1
tl;dr: I want to replace mine with a module that behaves similarly, but can emit customized sound themes, and/or be triggered with button(s) for e.g. pedestrian friendly horns.

I can't find the part on GM Parts Direct, but I want one to play around with first to understand how it works, and replicate the behavior of the OEM module. From what I can tell, the part listens on high speed GMLAN and drives a speaker output and a relay to switch which speaker receives output (front/rear).

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2020 model appears to have a different control module than prior model years.

Control module can be found beneath the center console:
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I'd like to have the module itself and, if possible, a length of severed cable ending in this connector:
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I don't think you can just lift it out of a functioning vehicle without maybe jumping high and low at the harness to reconnect high speed GMLAN loop? I'm not yet sure how exactly it works, but the schematic makes me think pulling it would leave the high speed GMLAN loop open:
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So ideally only pull out of an inoperable/wrecked vehicle maybe.

One or both speakers might also be nice to have on hand too:
Pedestrian Alert SOund Speaker - Front; At the front of the vehicle, in the middle behind the front
fascia:
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Pedestrian Alert Sound Speaker - Rear;
At the rear of the vehicle, on the left side near the wheel well, behind the rear fascia:
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Though I can't guarantee I'll ever get around to playing with it, and that it may sit around on my shelf for 10 years, I'd be willing to pay $50 for the control module, one or both speakers, and a length of the connector(s) off the harness, or $38 for just the control module?
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and that it may sit around on my shelf for 10 years,
Awesome post. Welcome to the forum. I've had my module sitting on my shelf now for four months. I have a 2017 so have the older module that I got off ebay. Since I have it right here near my computer I can read the part number as 42547472. Dr. Diesel posted a simple schematic that showed the com lines that suggested that the GMLAN passed through the unit.
 

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Discussion Starter #3
Thanks! I saw at GM Parts Direct the part for 2017 (42547472) and 2018-2019 (42527297), but they both list the compatible years, and I can't find the same part number for my own 2020 model year :/
Worst case I can go on Ebay and buy an older module if I don't find the 2020 variant and hack around with it like I intend and make some informed assumptions about the 2020 w.r.t. how it drives the relay switching forward/reverse. I've so far learned all I know of this module only from reading through the 2020 kinda-service-manual I picked up on EBay and a 2017 manual without all the missing pages.

What I'd like to do is connect it up on test bench, simulate GMLAN to the testbench unit (e.g. recorded by sniffing my own unit in-line? details tbd) and find out the basic functionality messages it listens in for (e.g. speed, accel, fwd/reverse), and then the hard part, create a small replacement module with a dev board of some sort and firmware I can control. Service manual details some scan tool data parameters the module should respond to in service mode, but no technical details, so I might only bother with those if it becomes a diagnostics problem, e.g. "Check Engine Light" because the module isn't responding to diagnostics correctly? ¯\(ツ)

In the High Speed GMLAN schematic part 1 & 2 you can see pretty clearly GMLAN passes through the unit, it's in the lower right of part 1. Pin 2 to Pin 7, and Pin 1 to Pin 6, so the pair of pins to the right of the connector facing the orientation as pictured in my post I'm guessing (I'm understanding this right maybe?) can be jumpered together so the module can be pulled out (probably) without affecting the rest of the car's functionality.

My only doubts being I genuinely didn't know anything about GMLAN or CAN bus before digging into this 😅😅 But now that I've got the ideas in my head, I really want to pursue this mod
 

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create a small replacement module with a dev board of some sort and firmware I can control.
Also, I believe this module provides the beep when plugging in the vehicle to charge. I was hoping to just read the IC chip numbers on the board and find their respective spec sheets. That didn't work out as planned. Seems to reason GM has a way of programming control modules which might include default sounds. At this point, have no idea if the sounds are programmable or just fixed in hardware. Flat out replacing the module would solve trying to figure out the one that came with the car.
 

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Discussion Starter #5
I did see there's (at least) three different sounds mentioned in scan tool info:
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I'm making the wild guess that they're not easily replaceable, at least not without deconstructing firmware.
The hardware schematics are easy enough to grok that I can imagine sniffing, filtering, and replaying CAN bus traffic to identify trigger events to the module, and subsequently replicating the same behavior in a drop-in replacement module seems the "easier" (funner, really) path :p

Programming instructions for the module in the service manual seems to be limited to "Follow the on-screen instructions" after the usual safety notes, e.g. likely just flashes factory firmware from a pre-made configurator.

Pedestrian Alert Description and Operation
Electric vehicles present a situation for visually impaired pedestrians who cannot hear an approaching electric vehicle, the pedestrian alert module creates sounds from a dedicated speaker to alert a visually impaired pedestrian, in a non-startling manner.

Operation of the Pedestrian Alert
  • {With Z49/EF7} Emit sound from 0 to 18 MPH (30 KM/H)
  • {Without Z49/EF7} Emit sound from 0 to 12 MPH (20 KM/H)
  • Fade in and out control for the sound ON and OFF
  • Change the pitch of the sound dependent of vehicle speed
I recognize that folks who pull the fuse have noted the charging chirp is affected by loss of the noisemaker, but it's interesting to note that the manual doesn't include that functionality in the description/operation details.
 

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I'm hoping someone, someday sells a speaker that we can mount under the hood in an easy accessible location that we can control via BT or however to play sound effects. I disabled my speaker, not the fuse method but the single wire/lead method (snip/cut).
 

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Discussion Starter #7
As far as I understood, the speakers it comes with may be just normal(-ish) speakers (YMMV). You might try splicing the wires going to pins 8 & 9 (annotated - and + in the schematic) with an RCA jack, or sleeve and tip of a 3.5mm TRS jack, and drive the speakers manually.

Toss in an Alexa Dot on 12V out, and turn your car into a rolling trolling Alexa 🤣
 

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tl;dr: I want to replace mine with a module that behaves similarly, but can emit customized sound themes, and/or be triggered with button(s) for e.g. pedestrian friendly horns.
Snake Jazz.

I have the 2017. How hard could it be? I DO know that when you yank the fuse the car doesn't care, so that's a huge bonus. Too bad it's buried somewhere completely horrible. Why couldn't it just be under the hood????

So here's a complete hack-y way to do it - What about just intercepting the speakers and having a Teensy or something get a basic "level" of the stupid audio coming out and generate / play back snake jazz in to a simple crappy class D amp. There's 12V in the front and 12V in the back (didn't realize there was a speaker in the back) so it's nowhere near as elegant or "cool" but it could be the path of least resistance and no farting around with the CAN bus.

Oh yeah and good luck finding that 10-pin connector. I didn't get encouraging results - Lots of obsoletes and discontinued and 53 week lead times. Some shells on ebay but no pins probably. I'm sure there's a trick, BUT the speaker connectors are on mouser and newark for like $1.50. Of course you'd never find the manual, but you can probably upload new wav files over the CAN bus to the thing, but good luck figuring that out.
 

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Discussion Starter #9
Snake Jazz.

I have the 2017. How hard could it be? I DO know that when you yank the fuse the car doesn't care, so that's a huge bonus. Too bad it's buried somewhere completely horrible. Why couldn't it just be under the hood????

So here's a complete hack-y way to do it - What about just intercepting the speakers and having a Teensy or something get a basic "level" of the stupid audio coming out and generate / play back snake jazz in to a simple crappy class D amp. There's 12V in the front and 12V in the back (didn't realize there was a speaker in the back) so it's nowhere near as elegant or "cool" but it could be the path of least resistance and no farting around with the CAN bus.

Oh yeah and good luck finding that 10-pin connector. I didn't get encouraging results - Lots of obsoletes and discontinued and 53 week lead times. Some shells on ebay but no pins probably. I'm sure there's a trick, BUT the speaker connectors are on mouser and newark for like $1.50. Of course you'd never find the manual, but you can probably upload new wav files over the CAN bus to the thing, but good luck figuring that out.
CAN doesn't seem too hard to muck about with. I had eyes on a Raspberry Pi hat to toy with the idea, but the one I wanted went out of stock and hasn't come back. Had that arrived, I'd have settled with a ~2017-2019 for playing with in the interim, but for now I'm waiting for either the Pi hat I wanted to be back in stock or a 2020 model year's module to show up here or on ebay.

Not long after I went down this path of research, I found this guy, Eric Reuter, who had put a VESS module from out of his Hyundai Kona EV on test bench and generated CAN bus frames at it with what looks like a Raspberry Pi:
And then rigged a Teensy to take the same data, translate to DCC, and emit locomotive noises out of a model train sound module:
https://www.reddit.com/r/CarHacking/comments/dookq7/_/f5p8p54 He even has switching PRNDL and some buttons emitting their own noises:
Once you're tapped into CAN bus, you have not just the data the stock module consumes, but other data from the same CAN bus loop of interconnected modules all communicating at one another to snoop on.

My figuring is there's already a module well situated in one place inside the cabin, while annoyingly beneath the whole center console assembly, at least has access to the cars' brain, the relay switching front/rear (for 2020 MY at least), and speakers, all connected through one harness connector. I'd rather go all in. I'm here for more than that snake jazz.

I wanna play with one on test bench and build something to replicate base functionality with my own featureset more or less plug & pray 😜 Having the spare module to test bench means I don't have to rip apart the car to get at my own until I'm ready to actually swap it out, but also it means the idea sits on the shelf of unfinished projects until I have a spare in hand, and I have some dev hardware with a CAN bus controller & transceiver.
 

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Discussion Starter #11
The CAN bus hat I wanted for the Raspberry Pi is back in stock, and I placed an order. Sometime after it arrives, I'll call parts department and see if they can't get me any testbench parts for a reasonable price, or at least a part number for 2020 MY, but fallback to an EBay listing if a 2020 module still doesn't show up. AFAICT the only meaningful difference may be the actuation of a relay to switch to rear speaker on reverse, and maybe the sound if the 2020 makes a distinct 2020 noise.

I'm hoping the module outputs sound to the speakers normally, and that the speakers are just ordinary rugged speakers made to survive their placement and purpose, and not actually specialized noise machines. If not, my project plan could become a little more complex than drop-in-replacement module 😜
 

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Discussion Starter #12
Just found this thread on sister Volt forum:

Module looks same/similar, there's def feasibility
 

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Module looks same/similar, there's def feasibility
I see it is located under the center console in the Bolt. I don't relish the idea of tearing these modern cars apart, with the plastic clips, and tabs. But if somebody produced a programmable module, I would take the risk to get my own sound on there.:)
 

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Discussion Starter #16
I see it is located under the center console in the Bolt. I don't relish the idea of tearing these modern cars apart, with the plastic clips, and tabs. But if somebody produced a programmable module, I would take the risk to get my own sound on there.:)
haha yeah, I don't look forward to that part either. If ever I actually see this project through the conclusion, I'll surely provide screenshots from the service manual copy I have w.r.t. how to tear out that center console! I've also seen another member here post about routing USB cable down through the console and up the tiny idfk pocket that could probably be used as photo reference.
 

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So it dawned on me that this discussion mentioned two speakers, one in the front wheelwell, and one in the rear. Anybody know when they added that "feature"? Our 2017 only has one in the front.
 
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