Program to record data from a cheap OBD2 scanner

[RScott]

Perhaps when I get some more time I'll tidy and publish the code, although, I'm not sure how much OnStar would appreciate that...

They will probably appreciate it as much as GM appreciating me starting to publish some of the OBD2 IDs. Whether or not they like it, there isn't much they can do about it. :)

[wizkid057]

They will probably appreciate it as much as GM appreciating me starting to publish some of the OBD2 IDs. Whether or not they like it, there isn't much they can do about it.

Well, with the OBD2 IDs, they can't do anything at all about it. However, I fear with the OnStar-based stuff (which actually uses their resources), they could eventually modify their end so that it can't be done as easily if it becomes an issue for them, which is why I would be hesitant to publicly post such code.

-wk

[wizkid057]

Here's how I convert the 4-byte latitude or longitude to a float ('mas' is milliarcseconds as an unsigned int):

if ( mas >= 0x40000000 )
{
	mymas = 0 - ( 0x80000000 - mas );
}

f = ( float )mymas / 3600000;

Hmm... I hadn't thought about treating it as signed without the sign bit set (0x80000000). Works well now, thanks.

-wk

[scottf200]

RScott is not using PID polling, he is doing passive scanning of the bus.
I've only found one PID for battery specific info

PID 01 5B
Type precent
Formula is
A*100/255

This gives raw battery SOC.

If you want battery as a usable percent (0=empty 100%=full) then try

PID 01 5B
min(100,max(0,(((A*100)/255-21)/65)))

Where the 21 is the lowest battery level you see and 86 is about the highest. (I;ve actually seen 20.5 and 87.6 but I think those were abnormal situations). <snip>

One of the coolest tech post ...
http://gm-volt.com/forum/showthread....1868#post91868

My first results that might be of interest from the DashDAQ OBD scanner, I eyeballed the transitions of each battery bar. The DashDAQ has at least two signals for battery level in the Volt extension driver, one for battery level % and one for the battery gauge %. The gauge turns out to map directly to the battery bars on the display, with each bar ticking off every 10% of the signal range (at least it did for the transactions I happened to watch - staring at the scanner while driving being a bad idea I haven't watched to confirm the entire series).

Here's how it maps between the gauge display and the actual battery SOC (or at least I think the VICM term is SOC).

Battery Gauge  Gauge %     Actual 16kWh Battery %
10 bars        91%-100%    81%-86.5%
9 bars         81%-90%     74.4%-81%
8 bars         71%-80%     68%-74.4%
7 bars         61%-70%     61.5%-68%
6 bars         51%-60%     55.3%-61.5%
5 bars         41%-50%     48.7%-55.2%
4 bars         31%-40%     42.1%-48.7%
3 bars         21%-30%     35.6%-42.1%
2 bars         11%-20%     29.3%-35.5%
1 bar           1%-10%     22.7%-29.3%
0 bars          0%-1%      20%-22.7%[/SIZE][/FONT]

The ICE comes on around 20% SOC, and the CS (Charge Sustaining) SOC is around 22%. So the ICE runs a bit to bring the SOC back up from 20%ish to 22%ish. This somewhat confirms some of what we've heard about the battery and battery SOC.

[Herto]

The program runs on Windows, so it requires a laptop/netbook running Windows. It works with the ELM327 v1.4 chipset, and requires a USB interface (not Bluetooth, which is not capable of the high speeds the Volt uses). The $30 ElmScan 5 at http://www.amazon.com/ElmScan-Compac.../dp/B002PYBZJO should do the trick. The program is just an executable file; hopefully, I'll be able to release the source as well at some point in the near future. You can download the executable online at http://www.evtools.info/exe/volt.exe.

Hi RScott,
Thank you for your work. I've tried your software with my Ampera.
It connects easily with my ELM327 (bluetooth), and looks to have no problem switching to 500kbps.
As long as the car is not started, it writes that it's waiting for CAN bus ( ___.___.___.__ ..). As soon as the car is started, it displays

E
Failed to read, car may be off. Continuing to read...
............

and it adds dots endlessly.
Is this normal?

[RScott]

Hi RScott,
Thank you for your work. I've tried your software with my Ampera.
It connects easily with my ELM327 (bluetooth), and looks to have no problem switching to 500kbps.
As long as the car is not started, it writes that it's waiting for CAN bus ( ___.___.___.__ ..). As soon as the car is started, it displays

and it adds dots endlessly.
Is this normal?

Sorry for the delay in responding.

The "Waiting for CAN bus" message is normal, but then once the car is turned on, the program should display an "E" and a number that updates continuously (representing the number of messages that the program has received).

The "Failed to read, car may be off" message indicates that the COM port that the OBD2 adapter uses is not sending any data (each "." represents another attempt to see if any data has been transmitted).

Do you have a link to a page that has information about the specific OBD2 adapter you are using? My understanding is that the Bluetooth adapters don't have enough bandwidth to transfer everything, but if that is the case, I would expect either the switch to 500kbps would fail or there would be some data (just not enough).

[Herto]

Here's what I bought : http://www.amazon.fr/gp/product/B005...ls_o00_s00_i00.
Is it a way to force your software to try another COM port (as the bluetooth modules creates more than one) ?

[RScott]

Here's what I bought : http://www.amazon.fr/gp/product/B005...ls_o00_s00_i00.
Is it a way to force your software to try another COM port (as the bluetooth modules creates more than one) ?

Hi,

Thank you for the link. I've gone ahead and ordered one that looks the same as yours, as it seems that most people prefer using Bluetooth so there are no cords. It will take a couple of days before I get it. Once I get it, I should have a much better idea of what the problem may be.

As for the COM port, there is no way to set it manually yet (although it shouldn't take too long to add, if needed), but from what is displayed, it sounds like it is getting the correct COM port.

[RScott]

It connects easily with my ELM327 (bluetooth), and looks to have no problem switching to 500kbps.
As long as the car is not started, it writes that it's waiting for CAN bus ( ___.___.___.__ ..). As soon as the car is started, it displays

and it adds dots endlessly.
Is this normal?

I just did a bit of testing, and was able to reproduce what you experienced, by connecting to the "wrong" OBD2 port. The Volt/Ampera has 2 OBD2 ports, one on the passenger's side, the other on the driver's side. In U.S. Volts, the one on the driver's side (left, as you are sitting in the car) is the one that has data that can be used. The one on the driver's side has data, but cannot be accessed with most OBD2 tools. When I plug the OBD2 interface into that one, I experience the results that you do.

I'm guessing that you have the steering wheel on the right side, and I'm also guessing that the OBD2 interface you want would be on the passenger's (left) side, but I could be wrong. So I would suggest trying to connect the OBD2 interface on the opposite OBD2 port, and see if that works.