For 1990-2009 cars

### 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 on the class 2 serial data circuit for approximately three seconds, U1305 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 voltage 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 class 2 messages are deteced on the class 2 serial data circuit.

• | The above condition is met for approximately three 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 U1305 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 U1305 will clear upon receipt of a scan tool Clear DTCs command.

### Diagnostic Aids

• | This DTC cannot be retrieved with a current status. The diagnosis of U1305 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 or voltage on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate with a Class 2 Device procedure in order to isolate an intermittent condition. Refer to Scan Tool Does Not Communicate with Class 2 Device .