For 1990-2009 cars

### DTC Descriptor

DTC U0073: High Speed Communication Bus

### Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle.

### Circuit/System Description

The high speed GMLAN serial data circuits are high speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. The high speed GMLAN serial data circuits also connect directly to the data link connector (DLC).

### Conditions for Running the DTCs

• | Supply voltage to the modules are in the normal operating range.

• | The vehicle power mode requires serial data communications.

### Conditions for Setting the DTC

The module setting the DTC has attempted to establish communications on the GMLAN circuits more than 3 times.

### Action Taken When the DTCs Sets

• | The module suspends all message transmission.

• | The module uses default values for all parameters received on the serial data circuits.

• | The module inhibits the setting of all other communication DTCs.

### 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 of 50, without a repeat of the malfunction.

### Diagnostic Aids

• | An intermittent condition is likely to be caused by a short on the high speed GMLAN serial data circuits.

• | This DTC cannot be retrieved with a current status. Diagnosis is accomplished using the symptom Scan Tool Does Not Communicate with High Speed GMLAN Device.

• | Refer to Data Link References.