For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC U1300: Class 2 Data Link Low
DTC U1301: Class 2 Data Link High
DTC U1305: Class 2 Data Link High or Low

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage
--- | --- | --- | ---
Class 2 Serial Data | U1300 | 1 | U1301
1. Some modules will set DTC U1305 if they are not capable of distinguishing between a short to battery voltage or ground.

### 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 seconds. When the module detects high or low voltage 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.

### 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

The class 2 serial data circuit is shorted high or low for approximately 3 seconds.

### Action Taken When the DTC Sets

The module uses a default value for the missing parameter.

### 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 Class 2 Device .

• | An intermittent condition is likely to be caused by a short on the class 2 serial data circuit.