U1128

DTC U1128 Loss Of Communications With Radio:

DTC U1128 Loss Of Communications With Radio (Part 1 Of 2):

DTC U1128 Loss Of Communications With Radio (Part 2 Of 2):

CIRCUIT DESCRIPTION
The serial data circuit is used to communicate information between systems. Each system connected to the serial data line is assigned its own recognition code (address). This code is used to identify which module or systems are communicating. Systems communicate with others by periodically sending a State of Health (SOH) message to each other. If the system sending the SOH message fails to receive a SOH message back, then a DTC identifying what system did not respond will set. Any system that also cannot communicate properly, will also store the appropriate communication DTC that was assigned to that system.

CONDITIONS FOR SETTING THE DTC
^ The Instrument Panel Cluster (IPC) sends out a State of Health (SOH) message to the Radio, and no SOH message response was sent back.
^ Condition must be present for 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ Stores a DTC U1128 in the IPC.
^ No driver warning message will be displayed for this DTC.

CONDITIONS FOR CLEARING THE DTC
^ This DTC requires an ignition cycle in order to change from current to history.
^ The IPC receives a SOH message back from the Radio.
^ A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present.
^ Use the IPC clearing DTCs feature.
^ Use a scan tool.

DIAGNOSTIC AIDS
^ If the problem is an intermittent loss of communications. Carefully inspect the serial data line and related components for the following intermittent conditions:
- There is an intermittent open or short (to ground or voltage) in the serial data line.
- Intermittent loss of communication with the Radio.
- Damaged or loose star connector terminals.
^ If the serial data line is shorted to ground or shorted to voltage, all systems connected to the same serial data line will not be able to communicate properly. Systems capable of storing loss of communication DTCs (DTCs with the letter U as a prefix) will have these codes stored in their memory. If a DTC U1128 is stored in the IPC, use a scan tool to monitor communications with the Radio. If the IPC loses communications with the Radio at any time, the IPC will store a DTC U1128. Test drive the vehicle while using a scan tool to monitor communications with the Radio can assist in diagnosing an intermittent malfunction. Check for an open in the serial data line between only the IPC and the Radio. The IPC and Radio must also be checked for intermittent operation due to a loss of power or ground. After repairing a DTC U1128, clear all DTCs from all systems capable of storing this DTC.
^ If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table:
2. This test checks if communications can be established between the scan tool and the Radio. If the scan tool cannot communicate with the Radio. Refer to Computers and Control Systems / System Check. Testing and Inspection
3. This test checks for a stored IPC DTC U1255. Conditions that set a DTC U1255 may also set a DTC U1128, therefore always diagnose a DTC U1255 first.
4. This test will check for any opens in the serial data line between the IPC and the Radio. It also checks for any intermittent malfunctions associated with the serial data line.