Cluster Illumination

WARNING: This page is about a different car, the 2005 Jeep Liberty. However, it is still accessible from the selected car via links, so may be relevant.

The EMIC has several illumination lamps that provide cluster back lighting whenever the exterior lighting is turned On. The illumination intensity of these lamps is adjusted when the interior lighting control ring on the left control stalk of the multi-function switch is rotated (down to dim, up to brighten) to one of six available minor detent positions. The Body Control Module (BCM) monitors a resistor multiplexed input from the multi-function switch on a panel lamps dimmer switch MUX circuit. In response to that input, the BCM provides a control output to energize the park lamp relay and transmits an electronic dimming level message to the EMIC over the Programmable Communications Interface (PCI) data bus based upon internal programming.

The EMIC receives the electronic dimming level message from the BCM, and a battery current input from the energized park lamp relay on the hard wired fused park lamp relay output. Based upon the dimming level message, the EMIC then converts the battery current input to the appropriate 12-volt Pulse Width Modulated (PWM) output. This PWM output is used to illuminate the cluster illumination lamps and the VFD unit on the EMIC circuit board, and provides a PWM output on the hard wired fused panel lamps dimmer switch signal circuit to control and synchronize the illumination intensity of other incandescent illumination lamps in the vehicle. The cluster illumination lamps are grounded at all times.

The BCM also transmits electronic dimming level messages over the PCI data bus to other electronic modules in the vehicle to control and synchronize the illumination intensity of their VFD units to that of the EMIC VFD unit. In addition, the control ring on the left (lighting) control stalk of the multi-function switch has a Parade Mode position to provide a parade or funeral mode. The BCM monitors the request for this mode from the multi-function switch, then transmits an electronic dimming level message to illuminate all VFD units in the vehicle at full (daytime) intensity for easier visibility when driving in daylight with the exterior lighting turned On.

The hard wired multi-function switch and panel lamps dimmer inputs to and outputs from the EMIC may be diagnosed using conventional diagnostic methods. However, proper testing of the PWM output of the EMIC and the electronic dimming level messages sent by the BCM over the PCI data bus requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.