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 U2100 00: Controller Area Network (CAN) Bus Communication

### Circuit Description

The GMLAN serial data circuits are controller area network (CAN) 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. On this vehicle there are 2 totally different types of GMLAN serial data circuits, the high speed 2-wire circuit and low speed single wire circuit. Refer to Data Link Communications Description and Operation for the complete description of these buses. The GMLAN serial data circuits also communicate directly to the DLC connector. 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. If the TEC value exceeds 255, the controller removes itself from the network and DTC U2100 will result.

### Conditions for Running the DTCs

• | 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 of 50, 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 the symptom, Scan Tool Does Not Communicate with High Speed GMLAN Device , or Scan Tool Does Not Communicate with Low Speed GMLAN Device depending on the module serial data communication.

• | An intermittent condition is likely to be caused by a short on the GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with High Speed GMLAN Device , or Scan Tool Does Not Communicate with Low Speed GMLAN Device procedure in order to isolate an intermittent condition.