For 1990-2009 cars
Data Link Communications Components
Data Link Connector Schematics
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### 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 high voltage on the class 2 serial data circuit for approxtmately three seconds, U1301 is set and the setting of all other class 2 serial communication DTCs is inhibited.

### 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 high.

• | The above conditions are 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 U1301 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 U1301 will clear upon receipt of a scan tool "Clear DTCs" command.

### Diagnostic Aids

• | This DTC cannot be retreived with a current status. Diagnosis of a current U1301 is accomplished via the symptom, Scan Tool Does Not Communicate With Components.

• | An interrmittent condition is likely to be caused by a short to ground on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate With Components procedure to isolate an interrmittent condition.