This Preliminary Information communication provides information to the technician for a service trailer brake message on in the vehicle. The technician will find diagnostic trouble codes C1115, C1116, C1117, or C1118. In most cases the chassis control module is not the cause of the trouble codes. The technician should inspect the wiring between the chassis control module and the trailer brake control switch. The inline connectors X185 or X138 as well as the connectors X1 and X5 of the X61A junction block should be thoroughly inspected looking for backed out, loose, poor retention or any other terminal issues. If there are no wiring concerns are found the trailer brake control switch is most likely the cause.
