National Instruments CAN 372139B-01 - Manual (Page 235)

Chapter 6 Automotive Diagnostic Command Set API for C
© National Instruments Corporation 6-71 Automotive Diagnostic Command Set User Manual
ndTesterPresent
Purpose
Executes the TesterPresent service. Keeps the ECU in diagnostic mode.
Format
long ndTesterPresent(
TD1 *diagRef,
LVBoolean *requireResponse,
LVBoolean *success);
Input
diagRef
Specifies the diagnostic session handle, obtained from ndOpenDiagnostic and passed
to subsequent diagnostic functions. Normally, it is not necessary to manually manipulate
the elements of this struct.
requireResponse
Indicates whether a response to this service is required. If *requireResponse is
FALSE, no response is evaluated, and success is always returned TRUE. This
parameter is passed by reference.
Output
success
Indicates successful receipt of a positive response message for this diagnostic service.
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 function to obtain a descriptive string for the return value.
Description
To ensure proper ECU operation, you may need to keep the ECU informed that a diagnostic
session is still in progress. If you do not send this information (for example, because the
communication is broken), the ECU returns to normal mode from diagnostic mode after a
while.