Waking up the bus so I can send OBD2 queries on GM


I am trying to send OBD2 queries to a Chevy Volt while the car is off. I can still get responses when the car is “awake” (for example, if I press the lock or unlock buttons on the key), but after about 30 seconds, it goes back to sleep, and nothing I send will wake it back up.

I can wake up the SWCAN bus by sending almost any frame, which is a start, and when I do that, I see one frame being repeated on CAN0 (ID 0x3ED, 6 bytes, 00 00 00 00 00 FF), which I don’t see when the car wakes up normally.

I have tried sniffing the bus while it is waking up, but I don’t see any special frames being sent, other than the 0x100 frame over SWCAN, which just seems to wake that bus up.

Is there an extra out-of-band signal I need to tap into somehow?


You need to change the mode of the SWCAN to HV wake up then send a frame ID of 100 00 00 00 00 00 00 00 00 then send a few frames with the ID’s of 62x 00 FF FF FF FF FF 00 00 or 62x 01 FF FF FF FF FF 00 00 then change the SWCAN mode back to normal then the bus on the car should be fully awake to query. The bus will go back to sleep after a min or so since the car is not powered on. I use this method to wake up the bus for my MyVoltStar app https://play.google.com/store/apps/details?id=com.thunkable.android.myvoltapp.MyVoltStar1


Thanks, brianbri6, that worked great! My problem was that I was taking it out of high voltage wakeup mode as soon as I sent the 0x100 frame.

I was able to figure out how to lock and unlock the doors using frame 0x1024E097, but I was unable to figure out how to start preconditioning - there’s just too much data on the bus, and I don’t have the resources to isolate the Onstar module to figure out which frames are coming from it.

Would you be willing to share some of the code used in your app for sending commands to the Volt?


Hi, jspenguin did you find a way how to start remote preheat?


I assume you’re talking about the preconditioning that can be done from the key and the OnStar app? Yes, it is possible to control that.

I had a bit of trouble with the command, so I tried to mimic exactly what the OnStar module sends. The frames I send are:

  1. Send wakeup frames to all the addresses I’ve ever observed over the wire: 0x620, 0x621, 0x622, 0x627, 0x62C, 0x62D. This is probably overkill.
  2. Wait until I start seeing activity on the high-speed bus.
  3. Send the following frame via SWCAN: 1024E097 00 01 FF (extended frame, 3 bytes). This is actually the door lock code, but OnStar sends it, so I do too.
  4. After 500ms, send 1024E097 80 01 FF. This is the actual command to start preconditioning.
  5. Wait 1000ms, then send 1024E097 00 00 FF. I’m not sure what this does, but OnStar sends it.

To cancel preconditioning, repeat the same steps, but send 40 01 FF instead of 80 01 FF in step 4.

Here’s a list of commands that can be sent:
00 01 FF - Lock all doors
00 02 FF - Unlock driver door
00 03 FF - Unlock all doors
02 00 FF - Open rear hatch
40 01 FF - Stop preconditioning
80 01 FF - Start preconditioning


Thanks for sharing,

but by some reasons it’s doesn’t work for me…

here is my code, maybe you find what i do wrong ?

#include <mcp_can.h>
#include <SPI.h>


byte wakeUp[8] = {0x01, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00};
byte battery[8] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
byte closeDoors[3] = {0x00, 0x01, 0xFF};
byte preheat[3] = {0x80, 0x01, 0xFF};
byte onstar[3] = {0x00, 0x00, 0xFF};

void setup()
if(CAN0.begin(MCP_ANY, CAN_500KBPS, MCP_16MHZ) == CAN_OK) Serial.println(“MCP2515 Initialized Successfully!”);
else Serial.println(“Error Initializing MCP2515…”);

void loop()
CAN0.sendMsgBuf(0x62, 0, 8, wakeUp);
CAN0.sendMsgBuf(0x620, 0, 8, wakeUp);
CAN0.sendMsgBuf(0x621, 0, 8, wakeUp);
CAN0.sendMsgBuf(0x622, 0, 8, wakeUp);
CAN0.sendMsgBuf(0x627, 0, 8, wakeUp);
CAN0.sendMsgBuf(0x62C, 0, 8, wakeUp);
CAN0.sendMsgBuf(0x62D, 0, 8, wakeUp);
CAN0.sendMsgBuf(0x100, 0, 8, battery);


CAN0.sendMsgBuf(0x1024E097, 3, closeDoors);

CAN0.sendMsgBuf(0x1024E097, 3, preheat);

CAN0.sendMsgBuf(0x1024E097, 3, onstar);



You need to use SWCAN, not CAN0. You also need to send the wakeup frames using mode 1. I don’t know what CAN library you’re using, so I don’t know how to do that. I’ll try to help later, I don’t have a lot of time right now.


i use this lib. https://github.com/coryjfowler/MCP_CAN_lib
thanks in advance


Also since the SWCAN library has been updated I can’t get any example sketch to compile without errors. Can someone break down real fast what has changed since it has been so poorly documented. Can someone upload working examples again? I was able to figure it out before now there is to many changes that don’t make sense.