Technical Service Bulletin PIT4593D — 2009 GMC YUKON

This Preliminary Information communication provides information to the technician about vehicles that have a lack of brake assist after disconnecting the battery or after the 12 volts battery has run low on voltage. The Antilock Braking System Malfunction Indicator Lamp may also be on. Technician may find Diagnostic Trouble Code C121D sym 00 or C056D sym 00 set in the Electronic Brake Control Module. Technician should be advised to wait for a period of at least 1 minute with the ignition in the "OFF" position prior to disconnecting the negative battery cable. Technician will need to follow these steps to repair the concern. 1. Install the negative battery cable to the battery. 2. Rotate the lever lock clockwise until an audible click is heard in order to connect the negative battery cable to the battery. 3. Position the negative battery cable insulating cover over the negative terminal. 4. Start the vehicle without stepping on the brake pedal. 5. Shut the vehicle "Off" for one minute. 6. Restart vehicle and check brakes for proper operation. 7. Clear codes in the Engine Control Module and the Electronic Brake Control Module.