DTC U1300, U1301, or U1305. GMC Truck GMC T-Series Medium Duty Truck F6/F7/F8 2007

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 one of the following conditions 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.

DTC	Condition
U1300	Low voltage on the class 2 serial data circuit
U1301	High voltage on the class 2 serial data circuit
U1305	High or Low voltage on the class 2 serial data circuit

DTC Descriptors

This diagnostic procedure supports the following DTCs:

•	DTC U1300 Class 2 Data Link Low

•	DTC U1301 Class 2 Data Link High

•	DTC U1305 Class 2 Data Link Low or High

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

•	No valid messages are detected on the class 2 serial data circuit.

•	The voltage level detected on the class 2 serial data circuit is under one of the following conditions:

High

Low

•	The above conditions are met for approximately 3 seconds.

Action Taken When the DTCs Sets

•	The module inhibits the setting of all other class 2 DTCs.

•	The module uses default values for all parameters received on the class 2 serial data circuit.

Conditions for Clearing the DTCs

•	Current DTCs will clear when a valid class 2 message is detected on the class 2 serial data circuit or at the end of the current ignition cycle.

•	A history DTC will clear when the module ignition counter reaches the reset threshold, with no repeated failure.

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 a Class 2 Device. Refer to 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. Use the Scan Tool Does Not Communicate with a Class 2 Device procedure in order to isolate an intermittent condition. Refer to Scan Tool Does Not Communicate with Class 2 Device .