Trailer Tow Module - Operation

OPERATION

The microprocessor within the Trailer Module (TM) (also known as the trailer connection unit, Trailer Lighting Module/TLM or AAG) contains the trailer tow lighting and electrical control logic. The TM uses On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with the diagnostic scan tool using the Controller Area Network (CAN) data bus. This method of communication is also used for trailer tow lighting and electrical control system diagnosis and testing through the 16-way data link connector located on the driver side lower edge of the instrument panel.

Pre-programmed decision algorithms allow the TM microprocessor to determine the appropriate trailer tow electrical control outputs based upon electronic message inputs received from the Body Control Module (BCM) (also known as the Signal Acquisition and Actuation Module/SAM) over the CAN data bus. When the programmed conditions are met, the TM provides voltage to the appropriate trailer tow lighting and electrical control circuits. These circuits feed the trailer circuits through dedicated trailer tow wiring in the vehicle and the trailer tow connector on the trailer hitch platform. The TM also provides electronic trailer connection status messages to other electronic modules in the vehicle over the CAN data bus.

In addition, the TM continuously monitors the resistance through each of the trailer lighting electrical output circuits, which allows the module logic to detect problems and determine the system readiness. If the TM detects a monitored system fault, it sets a Diagnostic Trouble Code (DTC) and sends the appropriate electronic messages to the BCM over the CAN data bus. The BCM responds to these messages by increasing the flash rate of the turn signal circuits and transmitting electronic messages to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN or KOMBI). The EMIC then provides feedback to the vehicle operator by increasing the flash rate of the turn signal indicators, increasing the click rate of a solid state relay that emulates the audible output of an electromechanical turn signal flasher, illuminating certain indicators and displaying certain fault messages.

The TM receives battery current through a fuse in the fuse and relay block within the driver side front seat riser frame, and receives ground at all times through a ground circuit and take out of the vehicle wire harness secured to the body sheet metal. These connections allow the module to be operational regardless of the ignition switch position.

The hard wired inputs and outputs of the TM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the TM or the electronic controls or communication between modules and other devices that provide some features of the trailer tow lighting system. The most reliable, efficient, and accurate means to diagnose the TM or the electronic controls and communication related to TM operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.