GM Service Manual Online
For 1990-2009 cars only

Circuit Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. In addition to this, Node Alive (State of Health) messages are transmitted by each module on the class 2 serial data circuit about once every two seconds. When the module detects no messages and a low voltage on the class 2 serial data circuit for approximately three seconds, U1300 is set and the setting of all other class 2 serial communication DTCs is inhibited.

Conditions for Running the DTC

    • Voltage supplied to the module is in the normal operating range (approximately 9 to 16 volts).
    • The vehicle power mode (ignition switch position) requires serial data communication to occur.

Conditions for Setting the DTC

    • No valid messages are detected on the class 2 serial data circuit.
    • The voltage level detected on the class 2 serial data circuit is low.
    • The above conditions are met for approximately 3 seconds.

Action Taken When the DTC Sets

    • The module inhibits the setting of all other class 2 DTCs.
    • The module uses default values for all parameters received on the class 2 serial data circuit.

Conditions for Clearing the DTC

    • A current U1300 will clear when a valid class 2 message is detected on the class 2 serial data circuit or at the end of the current ignition cycle.
    • A history U1300 will clear after 50 ignition cycles with no repeated failure.

Diagnostic Aids

    • This DTC cannot be retrieved with a current status. The diagnosis of U1300 is accomplished via the symptom, Scan Tool Does Not Communicate with a Class 2 Device. Refer to Scan Tool Does Not Communicate with Class 2 Device .
    • An intermittent condition is likely to be caused by a short to ground on the class 2 serial data circuit. Use Scan Tool Does Not Communicate with Class 2 Device to isolate an intermittent condition.