Clear DTC function is currently broken

[jLynx]

Right now the implementation of the clear DTC (#7) is broken and we are trying to work out how to get it to work. I am starting this issue thread so we can do a bit of a knowledge dump while we work out how to get it working.

Here are a few links to information that may be helpful.

http://www.totalcardiagnostics.com/support/Knowledgebase/Article/View/104/0/obd2-pids-for-programmers-technical
https://electronics.stackexchange.com/questions/561221/0x7e8-to-0x7fh-on-the-can-bus
https://en.wikipedia.org/wiki/OBD-II_PIDs
https://en.wikipedia.org/wiki/On-board_diagnostics

Here is the current implementation

ID: 0x7DF
Length: 8
Data: 0x00, 0x04x 0x00, 0x00, 0x00, 0x00, 0x00, 0x00

Based of the information in the Wikipedia article, this should work but in practice it does not seem to work.

[jLynx]

[jLynx]

0x04 also been used here https://github.com/Javadad01/obd2-instruments/blob/2ca7acc15b9f2b41a4f29c6f5f273607c6c1d010/obd2-instruments/common/obd2.c#L161

[areckicode]

Hi, seems you are missing the "data bytes" value in the message.
On byte 0 there is a number of data bytes and in your implementation you have "0", while you are sending 1 byte of data, which is the service number.
You can try to change the line 714 of the ODB2.cpp file to:
CAN.write(0x01); // number of additional bytes

So try sending the:
ID: 0x7DF
Length: 8
Data: 0x01, 0x04x 0x00, 0x00, 0x00, 0x00, 0x00, 0x00