Added function to clear diagnostic trouble codes (DTC)

[JasonJoyner01]

Created function to clear DTC codes from vehicle ECU using Service 04 functionality, using format documented at:

https://en.wikipedia.org/wiki/OBD-II_PIDs#Service_04
https://en.wikipedia.org/wiki/OBD-II_PIDs#Query

ECU should return 0 data bytes. PID not required. This is part of Open Issue #5

[sandeepmistry]

@tonkaman awesome work! Thanks for opening this pull request!

I've left a few minor comments, please let me know what you think!

[sandeepmistry]

We should add an entry for clearAllStoredDTC in both keywords.txt and API.md.

[JasonJoyner01]

I agree. I'll add the function to the keywords.txt file. How do you feel about this for the API.md?

Clear Stored Diagnostic Trouble Codes (DTC)

Clears any stored DTCs in the vehicle ECU, and turns off Malfunction Indicator Light (MIL, more commonly known as the Check Engine light).

int success = OBD2.clearAllStoredDTC();

Returns 1 if successful, or 0 on failure

[sandeepmistry]

@tonkaman updates look good!

I'm just going to make some minor style changes before merging.

[sandeepmistry]

@tonkaman awesome work!

[JasonJoyner01]

@sandeepmistry No problem. Eventually when I have time I want to tackle trying to read the DTC codes from a vehicle as well. That's not quite as simple as clearing them. Apologies for the messiness of my commits. This was my first time using Git, and I'm still learning the proper workflow.

[jLynx]

@tonkaman I was writing a reply on my issue on your repo, but you made it private so I could not do it. All I was going to say is I found that repo because of your PR here. I am going to test what I mentioned in your issue with am obd2 scanner and clear the codes and sniff the bus to see what command actually gets sent. I can then update you with what the command is from here if it differs

[JasonJoyner01]

Yes. I made it private because I realized it was unintentionally public. You were commenting on the wrong repo for that function. The repo you were commenting on was one I was still working on for converting OBDII diagnostic codes to text that describes what the code means. I’m a mechanical engineer by trade, so I’m still learning how GitHub works. Please update me with the results, and I’m glad to hear this is a useful idea.

[jLynx]

Hmm, this is really strange. I wasn't able to see the clear fault codes command when I executed it with my obd2 adapter

[JasonJoyner01]

I figured out how to purposely trigger a fault code on my 2011 Chevy Cruze by unplugging the O2 sensor. You are correct the function as written does not work. I'm stumped at the moment because I seem to get the response that it worked (returns 1), but the light doesn't go out on the dash. My guess is the message format is incorrect, but I can't find any documentation that's not behind an SAE or ISO paywall.

`
int OBD2Class::clearAllStoredDTC()
{
//Function clears stored Diagnostic Trouble Codes (DTC)

// make sure at least 60 ms have passed since the last response
unsigned long lastResponseDelta = millis() - _lastPidResponseMillis;
if (lastResponseDelta < 60) {
    delay(60 - lastResponseDelta);
}

for (int retries = 10; retries > 0; retries--) {
    if (_useExtendedAddressing) {
        CAN.beginExtendedPacket(0x18db33f1, 8);
    } else {
        CAN.beginPacket(0x7df, 8);
    }
    CAN.write(0x00); // number of additional bytes
    CAN.write(0x04); // Mode / Service 4, for clearing DTC
    CAN.write(0x00);
    if (CAN.endPacket()) {
        // send success
        break;
    } else if (retries <= 1) {
        return 0;
    }
}

return 1;

}
`

[jLynx]

Ok well at least I am not going crazy. I am really interested in trying to get this working.
I have been doing a bunch of research too and I can hardly find any documentation about it. The best I can do is find the Wikipedia page which is where you mentioned you got this info from too.

I wonder if there is another way to sniff the bus to get this info?
Also I think the reason why I couldnt sniff it is because in my 2003 BMW the OBD2 port doesn't have the CAN wires, so it must be communicating with something else for diagnostics. Sadly I dont have any other cars where I could test this out on.

[jLynx]

Just an idea. Does it need to do some sort of search/request for error codes before it can clear them? I am doubtful as it doesn't pass and specific data when it clears. but its just an idea

[JasonJoyner01]

I'm in the same boat. At least my Cruze is somewhat modern. My other vehicle is a 1997 pickup that predates CAN. My fiance also has a Cruze, so effectively we're limited to a single vehicle to test with at my house.

I'm going to keep trying things, but I think I might need to pony up the $85 for the 16 page SAE J2012_201612 document.

[jLynx]

Do you use Discord or something like that that we could collaborate a bit more together on @tonkaman ?