National Instruments CAN User Manual page 263

Return Value
The return value indicates the function call status as a signed 32-bit integer. Zero means the
function executed successfully. A negative value specifies an error, which means the function
did not perform the expected behavior. A positive value specifies a warning, which means the
function performed as expected, but a condition arose that may require attention.
Use the
ndStatusToString
Description
This function executes the ReportSeverityInformationOfDTC subfunction of the UDS
ReadDiagnosticTroubleCodeInformation service and reads the selected DTCs from the ECU
memory.
For further details about this service, refer to the ISO 15765-3 standard.
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Chapter 6
function to obtain a descriptive string for the return value.
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Automotive Diagnostic Command Set API for C
Automotive Diagnostic Command Set User Manual