DTC U1300, U1301, or U1305. Cadillac CTS 2005

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 Descriptors

•	DTC U1300 Class 2 Data Link Low

•	DTC U1301 Class 2 Data Link High

•	DTC U1305 Class 2 Data Link Low or High

DTC Symptom	DTC Symptom Description
00	No additional information

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 in one of the following conditions:

High

Low

•	The above conditions are met for approximately 3 seconds.

Action Taken When the DTCs Sets

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

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

•

These DTCs can be retrieved with a current status from engine control module (ECM) for LY7 and LP1 types only, because these ECMs communicate functionally on both class 2 and high speed GMLAN serial data circuits, but the communication with the scan tool is via high speed GMLAN. Diagnosis of current DTC 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 .