DTC U1128: Loss Of Serial Communications - IRC: Testing

If multiple class 2 DTCs are set as current (i.e., U1300, U1301, U1088 or U1153), check for an intermittent short to ground or battery in Purple wire. See WIRING DIAGRAMS .
If DTC is current, attempt to establish communication with IRC using scan tool. If communication cannot be established, diagnose and repair problem in audio system. If communication can be established, replace PZM. See REMOVAL & INSTALLATION.
If DTC is history, check for intermittent open in Purple wire between MMM and individual control modules. See WIRING DIAGRAMS .