The dash, also know as the instrument cluster, or IPC, illuminates the SERVICE VEHICLE SOON indicator light when the following things occur:
The body control module (BCM) detects certain malfunctions in the lighting system.
The IPC receives a class 2 message from the BCM requesting illumination.
The IPC sends a class 2 message to the BCM indicating that the service vehicle soon indicator is illuminated. The Body Control Module (BCM) sends a class 2 message to the radio in order to activate an audible warning.
The electronic brake control module (EBCM) detects a malfunction in the traction control system. The IPC receives class 2 messages from the EBCM requesting illumination of both the service vehicle soon and traction off indicators.
The IPC performs a display test at the start of each ignition cycle to the ON position. The indicator illuminates for approximately 3 seconds.
The IPC detects a loss of class 2 data communications with the BCM.
This is different from the Check Engine Light. The check engine light is a warning to problems in the PCM, engine control and emissions system.