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 messages are transmitted by each module on the class 2 serial data circuit about once every 2-5 seconds. When the module detects one of the following conditions on the class 2 serial data circuit for approximately 3 seconds, the setting of all other class 2 serial communication DTCs is inhibited and a DTC will set.

DTC | Condition
--- | ---
U1300 | Low voltage on the class 2 serial data circuit.
U1301 | High voltage on the class 2 serial data circuit.
U1305 | Either high or low voltage on the class 2 serial data circuit. Some modules will set DTC U1305 if they are not capable of distinguishing between a short to battery voltage or ground.

### Conditions for Running the DTCs

• | Voltage supplied to the module is in the normal operating voltage range.

• | The vehicle power mode requires serial data communication to occur.

### Conditions for Setting the DTCs

• | No valid messages are detected on the class 2 serial data circuit.

• | The voltage level detected on the class 2 serial data circuit is in one of the following conditions:

- | High

- | Low

• | The above conditions are met for approximately 3 seconds.

### Action Taken When the DTCs Sets

The module uses default values for all parameters received on the class 2 serial data circuit and all other DTCs are inhibited.

### Conditions for Clearing the DTC

• | A current DTC clears when the malfunction is no longer present.

• | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

### Diagnostic Aids

• | These DTCs cannot be retrieved with a current status. Diagnosis of current DTCs 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 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 .