U1301

Circuit Description
The link for serial data communications during normal vehicle operation is monitored by modules connected to the Class 2 serial data link. Operating information and commands are exchanged among the modules. The Node Alive (State of Health) messages are transmitted by each module on the Class 2 serial data link about once every 2 seconds. The U1301 is set. When the module detects no messages and a high voltage on the Class 2 serial data link for approximately 3 seconds, all of the other Class 2 serial communication DTCs are set.

Conditions for Setting the DTC
- Voltage is supplied to the module in the normal operating voltage range of approximately 9 - 16 Volts.
- No valid Class 2 messages are detected on the Class 2serial data link.
- The voltage level detected on the Class 2 serial data link is high.
- The above conditions are all met simultaneously for 3 seconds.

Action Taken When the DTC Sets
- The module inhibits the setting of all other Class 2 DTCs.
- DTC U1301 is set by the module.

Conditions for Clearing the DTC
- When a valid Class 2 message is detected on the Class 2serial data link or at the end of the current ignition cycle, a current U1301 will clear.
- A history U1301 will clear upon receipt of a scan tool CLEAR DTCs command.

Diagnostic Aids
This DTC may not be retrieved with a current status. Diagnosis of a current U1255 is accomplished via the symptom. The scan tool will not communicate with a Class 2 device. An intermittent condition is likely to be caused by a short to voltage on the Class 2 serial data link.