A DTCs are read in only one of following two ways:

The ESC module has the ability to store DTCs as current or history codes. Most RTD system malfunctions will display a message on the IPC and set a DTC. The message will remain on until the RESET button is pressed on the DIC. As long as the DTC is current, the message will be displayed after each ignition cycle. The RESET button must be pressed again in order to bypass the message.