Unable to Deactivate Brake Boost System

A GDS2 error message stating “Request Rejected by the Control Module” may occur when trying to deactivate the brake boost system while performing the hydraulic brake system bleeding procedure on some 2019-2021 XT4 models. (Fig. 15)

Fig. 15

The error message may be caused by the B20 Brake Fluid Level Switch Connector and the B34D Engine Coolant Temperature Sensor 4 Connector being swapped during reassembly.

If these connectors are swapped, DTC C0049 (Low Brake Fluid Indicated) SYM05 (High Voltage/Open) will be stored in the Electronic Brake Control Module (EBCM) and P2AFF (Engine Coolant Temperature Sensor 4 Circuit High Voltage) will be stored in the Engine Control Module (ECM).

When connecting the Brake Fluid Level Switch (Fig. 16) and Engine Coolant Temperature Sensor 4 (Fig 17), be sure to verify that the connectors are in the correct location. Reverse the connections if necessary.

Fig. 16

Fig. 17

– Thanks to Calvin Kohring

Duramax Diesel Warm Engine Idle Knock Sound
Low Oil or Add Oil DIC Messages

Leave a Reply

Your email address will not be published. Required fields are marked *

*