U1128-Loss Of Serial Data Communication (IRC) - Cell Phone

DTC U1128-Loss Of Serial Data Communication (IRC):

CIRCUIT DESCRIPTION
While the ignition switch is in RUN, modules communicating on the Class 2 Serial Data Line send a State of Health (SOH) message every 2 seconds to ensure that the system is operating properly.

DTC WILL SET WHEN
The cellular telephone module does not receive a SOH message from the Radio (IRC) after three consecutive monitoring cycles.

DTC WILL CLEAR WHEN
The IRC transmits a SOH message to the cellular telephone module.

TROUBLESHOOTING HINTS
1. If there are multiple Class 2 DTCs (i.e. DTCs U1064, U1096, U1129), check for an intermittent short to power or ground in CKT l807 (PPL).
2. If DTC is current, attempt to establish communication with the IRC using a scan tool.
3. If the DTC is history, check for an intermittent open in CKT 1807 (PPL).
^ If communication cannot be established with the IRC, refer to Audio Systems. Radio/Stereo
^ If communication can be established with the IRC, replace Cellular Telephone Module.