The RTD system uses the information from other systems in order to execute certain functions. Therefore, in order to properly diagnose the RTD system, a thorough understanding of the computer system and how each of the individual systems interacts with the RTD system is necessary before attempting any diagnostic procedure. Review the basic information on how the RTD system operates and how this system is used for diagnosis. This will save diagnostic time and prevent unnecessary parts replacement. Use a scan tool in order to diagnose the RTD System when referred to in diagnostic procedures. In addition to displaying DTCs, the scan tool displays the input status and the data values used by the RTD system. The scan tool is also capable of commanding the RTD system to cycle output components ON and OFF. Any of these features can be selected using scan tool diagnostic feature.

The RTD system does not have a malfunction indicator lamp, but instead uses the Instrument Panel Cluster (IPC) for the display functions. When the RTD system detects a malfunction that sets a DTC, the RTD system sends a message on the serial data line (directly or through the PCM) to the IPC, which will display one of the following messages:

The SHOCKS INOPERATIVE message will only be displayed if the RTD system detects a malfunction that sets a DTC and causes the RTD system to disable all four shock absorbers. The RTD system will send a message on the serial data line to the IPC to display this message.

The SERVICE RIDE CONTROL message will be displayed if the RTD system detects any malfunction that sets a DTC. The RTD system will send a message on the serial data line to the IPC to display this message.

The MAXIMUM SPEED message will only be displayed if the RTD system detects a malfunction that sets a DTC and causes the RTD system to disable all four shock absorbers. The RTD system will send a message on the serial data line to the PCM indicating that all four shock absorbers were disabled. The PCM then sends a message to the IPC to display the MAXIMUM SPEED message.

The ESC module has the ability to store Diagnostic Trouble Codes (DTCs) as current or history codes. Most RTD system malfunctions will display a message in the IPC and set a DTC. The message will remain ON until the RESET button is pressed on the Driver Information Center (DIC). As long as the DTC is current, the message will be displayed after every ignition cycle and the RESET must be pressed to bypass the message. History DTCs are intermittent malfunctions and must be diagnosed different then current DTCs. Refer to Intermittents and Poor Connections for a complete description on how history DTCs are used to diagnose intermittent malfunctions. If no current or history DTCs are stored in the ESC module, or if no communications can be established with the RTD system, refer to the RTD Diagnostic System Check before attempting any diagnostic procedures.

The RTD. system uses an ignition cycling diagnostic approach in order to reduce the occurrence of false or intermittent DTCs that do not affect the functionality of the RTD system. This allows for the fail-soft actions to be taken whenever a malfunction condition is current, but requires the malfunction to be current for a certain number of ignition cycles before the corresponding malfunction code and message will be stored or displayed.

If the RTD detects a malfunction, the RTD system defaults with a fail-soft action. A fail-soft action refers to any specific action the RTD system takes in order to compensate for a detected problem. A typical RTD fail-soft action would be if the RTD system detects a malfunction with the ride control switch, the RTD system will ignore this input and fail-soft to the SPORT ride setting. Refer to the applicable DTC description to determine what ride setting (TOUR, SPORT, PERF) the DTC will fail-soft to.