How to read the dtc codes

[shivpj]

Hello,
How to read the dtc codes?

int OBD2Class::ReadDtcs(uint8_t mode, void* data, int length)
{
// 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(0x02); // number of additional bytes
CAN.write(mode);
//CAN.write(pid);
if (CAN.endPacket()) {
// send success
break;
} else if (retries <= 1) {
return 0;
}
}
bool splitResponse = (length > 5);
for (unsigned long start = millis(); (millis() - start) < _responseTimeout;) {
if (CAN.parsePacket() != 0 &&
(splitResponse ? (CAN.read() == 0x10 && CAN.read()) : CAN.read()) &&
(CAN.read() == (mode | 0x40))) {

  _lastPidResponseMillis = millis();

  // got a response
  if (!splitResponse) {
    return CAN.readBytes((uint8_t*)data, length);
  }
  int read = CAN.readBytes((uint8_t*)data, 3);
  for (int i = 0; read < length; i++) {
    delay(60);

    // send the request for the next chunk
    if (_useExtendedAddressing) {
      CAN.beginExtendedPacket(0x18db33f1, 8);
    } else {
      CAN.beginPacket(0x7df, 8);
    }
    CAN.write(0x30);
    CAN.endPacket();
    // wait for response
    while (CAN.parsePacket() == 0 ||
           CAN.read() != (0x21 + i)); // correct sequence number
    while (CAN.available()) {
      ((uint8_t*)data)[read++] = CAN.read();
    }
  }
  _lastPidResponseMillis = millis();
  return read;
}

}

return 0;
}

I have added a function like this. While running this function, there is no output. could you please suggest any changes.

Thanks

[shivpj]

Hello,
Is the above code is correct to read the stored dtc codes?

[se-pulvirenti]

hi,
you removed the pids byte, try the following:
CAN.write(0x01); // number of additional bytes

[shivpj]

hi,
you removed the pids byte, try the following:
CAN.write(0x01); // number of additional bytes

Thanks for the response, I tried but the above function returned zero (0). I used this PID to get the status of the DTC codes.

It returned "516352" value. As per below table.

How should I encode this value.

[se-pulvirenti]

Hi,
I tried on my car, it returns 0 but actually I don't have DTC code, like in your case:
516352 = binary 00000000 00000111 11100001 00000000
A = 00000000
B = 00000111
C = 11100001
D = 00000000
A7 is 0 (it means that the warning light on the dashboard is off)
A6-A0 is 0 (no DTCs)

[fsu-icx]

Hi,
Could you please provide an example as to how this function can be used to read DTCs?
I don't understand the arguments I have to pass, besides 0x03 to select mode 3.

Thanks !

[skndungu]

That function is incomplete to read DTCs you have to do more work than what is done there

[fsu-icx]

Thank you for the reply!

Yes this is what I suspected, sadly I don't have the skill to complete the function, I tried but I'm too far off :)

Too bad Sandeep's great library doesn't provide this feature though.

Cheers!

[BenjaminMuslic]

Can someone look into implementing reading DTCs?

[skndungu]

@BenjaminMuslic it's way complicated that it seems and more so custom to each vehicle make, apart from OBD2 emmission related DTCs