U1300

DTC U1300, U1301, or U1305

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

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

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description.






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

This DTC can be retrieved with a current status from the body control module (BCM) only, because the BCM is the gateway between the class 2 and high speed GMLAN serial data circuits and the BCM diagnostics is performed on high speed GMLAN link. Refer to Data Link Communications Description and Operation for more information about data link communication.

Test Description

Step 1 - Step 7:

Step 8 - Step 15:

Step 16 - Step 19:

The numbers below refer to the step numbers on the diagnostic table.
7. The class 2 serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wire for a short, make sure there is not a module connected to the wire being tested. This test isolates the splice pack SP205 serial data circuits.
13. This test isolates the splice pack SP208 serial data circuits.
16. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
17. The communication malfunction may have prevented diagnosis of the customer complaint.