Principles of Operation

The instrument cluster is a configurable, hybrid electronic cluster (HEC) that contains a microprocessor, gauges, indicator lamps, backlighting lamps and internal circuitry. The instrument cluster is non-repairable at the dealership level with the exception of the warning indicator bulb, the backlighting bulb and the instrument cluster lens replacement. The instrument cluster utilizes hardwired circuitry, the standard corporate protocol (SCP), and UART based protocol (UBP) communication networks. Communication using the SCP network transmits and receives data between the instrument cluster and the PCM. Communication using the UBP network utilizes data transmitted and received by the instrument cluster and the body security module, driver seat module and the electronic air temperature control (EATC).

It is very important to understand:

• where the input originates from.
• all the information necessary in order for a feature to operate.
• which module(s) receive(s) the input or command message.
• whether the module which received the input controls the output of the feature, or whether it outputs a message over the SCP or UBP network to another module.
• which module controls the output of the feature.

The instrument cluster carries out a display prove-out to verify that the warning/indicator lamps and monitored systems are operating correctly. When the ignition switch is turned to the ON position with the engine off, the following indicators will illuminate:

• LOW RANGE indicator
• 4x4 high indicator
• BRAKE warning indicator
• malfunction indicator lamp (MIL) indicator
• check fuel cap indicator
• CHECK GAGE warning indicator
• door ajar indicator
• low fuel warning indicator
• safety belt warning indicator
• wait to start indicator
• water in fuel indicator