The C5 has hundreds of DTC's (Diagnostic Trouble Codes).  The codes can be read from the DIC's 20 character display. Here is how:

1. Turn ignition ON, engine OFF.
2. Press the RESET button to acknowledge any warning messages that may be present.
3. Press the OPTIONS button on the Driver Information Center (DIC) and hold.
4. While holding the OPTIONS button, press the FUEL button 4 times with a 10 second period.
5. System will enter the automatic display mode.

The DTC's are arranged by systems as follows:
 

PCM - Powertrain Control Module

TCS - Traction Control System

RTD - Real Time Damping

BCM - Body Control Module

IPC - Instrument Panel Cluster

RADIO -Radio

HVAC - Heater, Ventilation and Air Conditioning

LDCM - Left Door Control Module

RDCM - Right Door Control Module

SCM - Seat Control Module

RFA - Remote Function Actuation

Automatic display mode, shows codes (if any) for each of the above systems and then stops in manual display mode. Manual mode can be entered at any time by pressing any key except E/M.

In manual display mode, the keys operate as follows:
 

FUEL - Previous DTC

GAGES - Next DTC

TRIP - Previous System

OPTIONS - Next System

E/M - Exit Diagnostics

RESET - Clear DTC's

The DTC's are needed by your dealer for diagnostics.  So do not reset them unless you know you created them.

Click here for a List of IPC Display Functions and Codes