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Home >> Ford >> 2009 >> F 450 2WD Super Duty V8-6.4L DSL Turbo >> Repair and Diagnosis >> Relays and Modules >> Relays and Modules - Brakes and Traction Control >> Trailer Brake Control Module >> Testing and Inspection >> Initial Inspection and Diagnostic Overview >> Principles of Operation
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Principles of Operation




Auxiliary Brake System - Trailer Brake Control (TBC) Module


Principles of Operation

The Trailer Brake Control (TBC) module is an integrated electronic control device that is designed to provide variable braking power to the electric-actuated drum brakes on a towed trailer (1 to 4 axles only). The braking energy that is provided to the trailer is varied with a Pulse Width Modulated (PWM) signal that switches between 0 volt and battery voltage, the higher the duty cycle the more braking power available.

The TBC module receives information from 3 different brake pedal inputs: the Brake Pedal Position (BPP) switch, the brake pressure switch (also known as the speed control deactivation switch) and the brake pressure transducer.

The BPP switch is mounted on the brake pedal bracket and switches on or off depending on the brake pedal position. The brake pressure switch is mounted on the bottom of the master cylinder near the front and switches on or off depending on the pressure applied on the brake pedal. The TBC module receives both the BPP and the brake pressure switch information over the High Speed Controller Area Network (HS-CAN) bus from the PCM.

The brake pressure transducer is mounted on the bottom of the master cylinder near the rear and sends a variable voltage to the TBC module depending on the pressure applied to the brake pedal. The TBC module receives this information directly from the pressure transducer.

The TBC module receives information through the HS-CAN bus. These inputs are from the PCM, the Instrument Cluster (IC) and the ABS module. The information sent out from the TBC module is through the IC and is displayed on the message center.

To adjust the gain setting up or down, the TBC module faceplate provides the driver with control buttons which determine the maximum power output sent to the 14-pin connector. The TBC module faceplate also provides a manual control lever to manually apply the trailer brakes, independent of the vehicle brakes, to calibrate the gain setting to the specific trailer loading and road conditions. Note that when the manual control is activated, both the center high-mounted stoplamp and the trailer brake lamps illuminate. If a trailer is not connected and the manual control lever is activated, the vehicle center high-mounted stoplamp will still illuminate.


Instrument Cluster (IC) Configuration For Trailer Brake Control (TBC) Functionality

The same IC is used for vehicles with and without the TBC option. TBC functionality is enabled or disabled using the scan tool. If the vehicle is equipped with a TBC module, but the IC was not configured for TBC, the TBC module will shut down, no TBC information will be displayed in the message center and DTC U2202 will set in the TBC module.

If the IC is configured for TBC, but the vehicle is not equipped with a TBC module, TRAILER BRAKE MODULE FAULT will be displayed in the message center. This symptom could occur if a replacement IC was installed, but not configured correctly. For additional information on the TBC programmable parameter, refer to Programmable Parameters in Inspection and Verification. Programming and Relearning


Trailer Brake Control (TBC) System Message Center Messages

The IC message center provides the gain setting and relative braking power during a braking event. The message center will also indicate trailer connectivity and trailer wiring faults. The following message center messages pertain to the TBC system:

- NO TRAILER - This message is displayed and accompanied by a single chime whenever the ignition is cycled from OFF to RUN without a trailer connected to the 7-pin trailer connector.
- TRAILER CONNECTED - This message is displayed when a correct trailer connection at the 7-pin trailer connector has been made during a given ignition cycle.
- OUTPUT - When the vehicle brake pedal is pushed, or when the manual control is activated, bar indicators will illuminate in the message center to indicate the amount of power going to the trailer brakes relative to the brake pedal or manual control input. One bar indicates the least amount of output with 6 bars indicating maximum output.
- TRAILER DISCONNECTED - This message is displayed and accompanied by a single chime when a correct trailer connection was made and then a disconnection has been sensed during a given ignition cycle. This message will display if the 7-pin trailer connector becomes disconnected while driving. This message can be displayed if an intermittent open circuit occurs in the vehicle wiring from the TBC module to the 7-pin trailer connector or the trailer wiring. This message is also displayed during manual activation using the manual control lever without a trailer connected.
- TRAILER BRAKE MODULE FAULT - This message is displayed when a fault is detected by the TBC module. A DTC will be stored in the TBC module when this message is displayed.
- WIRING FAULT ON TRAILER - This message is displayed when the trailer brake output circuit is shorted to ground or shorted to voltage. A DTC will be set in the TBC module indicating which circuit fault was observed. It is important to determine if a trailer was connected when this message was displayed. If this message is only observed with a trailer is connected, problem is related to the trailer wiring and not the vehicle. If this message is observed without a trailer connected, the problem is with the vehicle wiring from the TBC module to the 7-pin trailer connector.

Trailer Brake Control (TBC) Module Wake Up

NOTE: These conditions require that a trailer is not connected to the trailer tow connector.

The following conditions describe the normal operation of the TBC module at start up.

When the ignition key is in the RUN position and the manual lever is set all the way to the left with a gain of 10, without a trailer connected to the vehicle, the message center should display TRAILER DISCONNECTED. At the same time, with the vehicle stationary, battery voltage should be present at pin-3 of trailer tow connector C4099.

Every 4 seconds the TBC module sends a voltage pulse along circuit CAT19 (BU) to pin-3 of trailer tow C4099 to determine whether a trailer is connected to the trailer tow connector.
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