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 Descriptor

DTC U0073 00: Control Module Communication Bus Off
DTC U0073 71: ECU HS Bus Off
DTC U0073 72: ECU LS Bus Off
DTC U2100 00: Controller Area Network (CAN) Bus Communication
DTC U2100 47: Controller Area Network (CAN) Bus Communication

### Circuit/System Description

The serial data circuits are serial data buses are used to communicate information between the control modules. The serial data circuits also connect directly to the data link connector (DLC).

### Conditions for Running the DTCs

• | Supply voltage at 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 serial data 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.

### Circuit/System Verification

1. Refer to Data Link References to determine which serial data system is used for a specific module.
2. 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 or Scan Tool Does Not Communicate with Low Speed GMLAN Device .