For 1990-2009 cars

### Circuit Description

The GMLAN serial data circuits are controller area network (CAN) high and/or low 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. There are two different types of GMLAN serial data circuits, the High speed 2-wire circuit and Low speed single wire circuit. The GMLAN serial data circuits also communicate directly to the data link connector (DLC). Messages are interpreted by the externally connected CANdi module which acts as a transceiver for the scan tool.

Modules connected to the GMLAN serial data circuits monitor communications during normal vehicle operation, where operation information is exchanged among the modules. All the modules on the GMLAN networks, maintain a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages.

### DTC Descriptors

DTC U0073: Controller Area Network (CAN) Bus Communication
DTC U2100: Controller Area Network (CAN) Bus Communication

### Conditions for Running the DTC

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

• | The vehicle is in the RUN power mode.

### Conditions for Setting the DTC

The module setting the DTC has attempted to establish communications on the GMLAN circuits for more than 7 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, without a repeat of the malfunction.

### Diagnostic Aids

This DTC cannot be retrieved with a current status. Diagnosis of a current DTC is accomplished via Scan Tool Does Not Communicate with High Speed GMLAN Device . Refer to Data Link References for the correct procedure for the specific module(s) and the busses they use to communicate.

### Reference Information

#### Schematic Reference

Data Communication Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Data Link Communications Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool References

Control Module References for Scan Tool Information