F 350 4WD Super Duty V8-6.4L DSL Turbo (2008)
Trailer Brake Control Module: Initial Inspection and Diagnostic Overview
Principles of Operation
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 on/off (BOO) switch, the brake pressure switch (also known as the
speed control deactivation switch) and the brake pressure transducer.
The BOO 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 BOO and the brake pressure switch information over the high speed communication 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 and the ABS module. The
information sent out from the TBC module is through the HS-CAN and is displayed on the instrument cluster 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 (CHMSL) and the trailer brake lamps illuminate. If a trailer is not connected and the manual control lever is activated, the
vehicle CHMSL will still illuminate. The TBC module faceplate displays the gain setting and relative trailer braking power during a braking event. The
TBC module also has an illuminated red or green trailer icon that displays the trailer connectivity status to the driver.
TBC Module Start Up, Prove Out and 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.
TBC Module Start Up and Prove Out
When the ignition is turned to the RUN position, the TBC module display will prove out by illuminating all the LEDs. At the same time, the TBC
module will check the instrument cluster for trailer brake configuration.
If the instrument cluster is not configured for trailer brakes, the TBC module will shut down and the TBC system will be inoperative (pressing the gain
button or sliding the manual lever will get no reaction from the TBC module), DTC U2202 will set in the TBC module and TBC FAULT will be
displayed on the instrument cluster. TBC is a programmable parameter in the instrument cluster. For additional information on programmable
parameters, refer to Module Configuration in Information Bus (Module Configuration).
If the instrument cluster is configured for trailer brakes and a trailer is not connected to the vehicle, then the red trailer icon will illuminate. At this time,
pressing the gain button or sliding the manual lever will only activate the TBC, it will not input a gain setting or activate the trailer brakes. A second
press of the gain button will be necessary to input a gain setting into the TBC or a second movement of the manual lever will be necessary to apply the
trailer brakes.
TBC Module Wake 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 TBC module LEDs should illuminate and the message center (if equipped) 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.
Inspection and Verification
NOTE: A trailer brake emulator tool is available to verify that the TBC module and vehicle wiring are functioning correctly.
1. Verify the TBC system is correctly installed by checking that the vehicle is equipped with a brake pressure transducer on the master cylinder. If the
brake pressure transducer is not present, then the TBC system has been installed incorrectly.
2. Verify the customer concern.
