Trailer Brake Warning
This bulletin applies to 2014-2017 GMC Sierra 1500 and Yukon models with integrated trailer brake systems. Some owners may comment on a Service Trailer Brake message in the DIC.
When checking for DTCs, a U0415 “Invalid Data Received from Electronic Brake Control Module” may be set in the Chassis Control module. It may also be noticed that this message occurs during hard braking, acceleration and/or turns.
The concern could be caused by the brake fluid level near the minimum level. The brake fluid level sensor may momentarily signal the brake fluid level is low as the brake fluid sloshes in the master cylinder reservoir during acceleration, hard braking or turns.
The brake fluid level sensor is a direct input to the EBCM. The EBCM sends the brake fluid level data to the chassis control module via the high speed LAN communication bus. When the chassis control module receives the message that the brake fluid level was low, it sets DTC U0415 and commands the “service trailer brake” message on. Fill the master cylinder brake fluid reservoir to the maximum level mark.
The brake fluid level sensor data can be monitored using the scan tool (GDS2) under the EBCM antilock braking data list parameter “Brake Fluid Level Sensor.” It will display either “OK” or “LOW.”
Brake fluid level could be low due to normal brake pad wear or system leaks. If no brake fluid leaks are found and the issue was not caused by pad wear, inspect the rear of the master cylinder to check for fluid leaking into the brake booster.