Trailer Tow Module - Operation

OPERATION

The microprocessor within the Trailer Module (TM) contains the trailer tow lighting and electrical control logic circuits. The module 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 hard wired inputs from the brake lamp switch and the ignition switch as well as from electronic message inputs received from the Front Control Module (FCM) 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 continuously monitors the resistance through each of these electrical output circuits, which allows the module logic circuits to detect problems and determine the system readiness. If the module detects a monitored system fault, it sets a Diagnostic Trouble Code (DTC) and sends the appropriate electronic messages to the FCM over the CAN data bus. The FCM responds to these messages by increasing the flash rate of the turn signal circuits and transmitting electronic messages to the Electro Mechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN. The EMIC then provides feedback to the vehicle operator by increasing the flash rate of the turn signal indicators and increasing the click rate of a solid state relay that emulates the audible output of an electromechanical turn signal flasher.

The TM receives battery current on a fused B(+) circuit and a fused ignition switch output (run-start) circuit through fuses in the Junction Block (JB). The module receives ground through a ground circuit and take out of the body wire harness. 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.