System Operation - Integrated Trailer Control Module System

The Integrated Trailer Control Module (ITCM) is used on premium systems to operate the trailer lamps and trailer braking. The ITCM receives messages from the Body Control Module (BCM) indicating the status of the following lamp circuits:

• Park Lamps Command = On/Off
• Stop Lamps Command = On/Off
• Turn Signal Command = On/Off
• Back-up Lamps Command = On/Off
• Rear Fog Lamps (limited markets) Command = On/Off

When the ITCM receives a status message "ON" for one of the lamp circuits, the ITCM turns on a High Side Driver (HSD) control circuit supplying battery voltage to the trailer connector. The driver is turned on within 70ms of the command from the BCM. IF the ITCM receives a Turn Signal command "On" with the Brakes applied, the ITCM will pulse the appropriate Brake/Turn driver circuit in synchronization with the vehicle lighting (maximum acceptable delay of 70ms from the input CAN signal).

CONNECTIVITY DETECTION 

The ITCM monitors for trailer connectivity by monitoring the load on the driver circuits. If a load is detected on any driver circuit when commanded on, the ITCM determines that a trailer is connected. The ITCM will send a status message over the CAN bus for the BCM and instrument cluster indicating trailer connectivity. The ITCM also sends out the status of each driver circuit over the CAN bus. Trailer connectivity is continuously monitored in the following manner:

• The module monitors and detects connectivity to a trailer with the ignition on, when the vehicle is stationary. When the park lamp or either Brake/Turn Signal lamp input command is active, and no open circuit is detected on the driver circuit (manual process - input from operator), connectivity is detected. If no input from the operator is present the module will perform an automatic check and toggle on the brake, left turn signal and right turn signal to check for connectivity.
• If detection occurs the trailer "connected" status is set. The ITCM will begin monitoring the driver circuits for an open circuit condition. If no loads are detected on any of the driver circuits the "trailer not connected" status is set.
• After vehicle speed is detected with the trailer "connected" status set, if the ITCM detects an open circuit on all of the driver circuits it determines it has lost connection and a general failure status sets. This would happen if connector becomes disconnected within that drive cycle event before coming to a stop. A loss of ground could possibly set this condition as well. If an open is detected on one driver circuit, but a load is detected on other driver circuits, an open circuit fault will set against the driver.
• On the next vehicle stop the cycle starts over again to verify connectivity. The cycle occurs every time the vehicle speed shows that the vehicle is stopped.

The Integrated Trailer Control Module (ITCM) performs diagnostics and stores faults against the HSD output circuits. The short to voltage and short to ground diagnostics are continuous and do not require connectivity to a trailer. The open circuit diagnostic does not run until connectivity is detected.

TRAILER BRAKING 

The Integrated Trailer Control Module (ITCM) communicates with the vehicle through the high speed Controller Area Network (CAN C) bus. The ITCM monitors the Brake Pedal Status, Vehicle Speed and Electronic Stability Control (ESC) status via CAN message. It also outputs the Trailer Status, Gain Setting, and Trailer Brake Output Power to the vehicle. The ITCM connects to the electric trailer brakes through the 7-Way connector and controls the brake force through a Pulse Width Modulating (PWM) duty cycle. The ITCM PWM duty cycle output is present continuously.

The ITCM controls the PWM output to the trailer brakes in three ways:

1. Occurs when the brake pedal is active and vehicle speed is greater than 0 km/h (0 mph).
2. The Integrated Trailer Brake Switch (ITBS) manual lever, which can be controlled by the driver. If both the manual lever and the brake pedal are active simultaneously, the greater of the two, in terms of PWM output, will prevail.
3. It will become active during an ESC trailer sway event.