U1305

DTC 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 in Vehicle DTC Information. 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
These DTCs can be retrieved with a current status from engine control module (ECM) only, because ECM communicates functionally on both class 2 and high speed GMLAN serial data circuits, but ECM communication with the scan tool is via high speed GMLAN.

TEST DESCRIPTION

Steps 1 - 8:

Steps 9 - 16:

The numbers below refer to the step numbers on the diagnostic table.
4. This step takes out from the class 2 bus the modules connected to splice pack SP304.
5. This step takes out from the class 2 bus the modules connected to splice pack SP300.
6. This step takes out from the class 2 bus the modules connected to splice pack SP200.
7. This test localizes the short on the rest of modules/circuits still connected to class 2 circuits of the ECM.
14. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.
15. The communication malfunction may have prevented diagnosis of the customer complaint.