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.
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 |
• | Voltage supplied to the module is in the normal operating voltage range. |
• | The vehicle power mode requires serial data communication to occur. |
• | 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. |
The module uses default values for all parameters received on the class 2 serial data circuit.
• | 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. |
• | These DTCs cannot be retrieved with a current status. Diagnosis of the 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 . |
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.
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 |
• | Voltage supplied to the module is in the normal operating voltage range. |
• | The vehicle power mode requires serial data communication to occur. |
• | 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. |
• | The module uses default values for all parameters received on the class 2 serial data circuit. |
• | The setting of all other class 2 serial communication DTCs is inhibited. |
• | 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. |
This DTC can be retrieved with a current status from the engine control module (ECM) only, because the ECM is the gateway between the class 2 and high speed GMLAN serial data circuits, and the ECM diagnostics is performed on high speed GMLAN link. Refer to Data Link Communications Description and Operation for more information about data link communication.
The numbers below refer to the step numbers on the diagnostic table.
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 SP306 serial data circuits.
This test isolates the splice pack SP205 serial data circuits.
If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
The communication malfunction may have prevented diagnosis of the customer complaint.
Step | Action | Yes | No |
---|---|---|---|
Schematic Reference: Data Communication Schematics Connector End View Reference: Master Electrical Component List | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
2 | Did you record U1300 or U1301, as current? | Go to Step 4 | Go to Step 3 |
3 |
Important: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions. Test the class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following: Did you find and correct the condition? | Go to Step 22 | -- |
4 |
Does the scan tool communicate with BCM? | Go to Step 18 | Go to Step 5 |
5 |
Did you record U1300 or U1301, as current? | Go to Step 8 | Go to Step 6 |
Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP306 until the concern is located:
Did you record U1300 or U1301, as current? | Go to Step 7 | Go to Testing for Intermittent Conditions and Poor Connections | |
7 |
Did you find and correct the condition? | Go to Step 20 | Go to Step 18 |
8 |
Did you record U1300 or U1301, as current? | Go to Step 9 | Go to Step 12 |
9 |
Did you record U1300 or U1301, as current? | Go to Step 11 | Go to Step 10 |
10 |
Did you find and correct the condition? | Go to Step 20 | Go to Step 16 |
11 |
Did you find and correct the condition? | Go to Step 20 | Go to Step 16 |
12 |
Did you record U1300 or U1301, as current? | Go to Step 13 | Go to Step 14 |
13 |
Did you find and correct the condition? | Go to Step 20 | -- |
Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP205 until the concern is located:
Did you record U1300 or U1301, as current? | Go to Step 15 | Go to Testing for Intermittent Conditions and Poor Connections | |
15 |
Did you find and correct the condition? | Go to Step 20 | Go to Step 18 |
16 | Inspect for poor connections at the class 2 serial data circuit of the VTD, if equipped, or BCM, if not equipped with VTD. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 20 | Go to Step 17 |
17 | Replace the VTD, if equipped, or BCM, if not equipped with VTD. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 20 | -- |
18 | Inspect for poor connections at the class 2 serial data circuit of the last disconnected module. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 20 | Go to Step 19 |
19 | Replace the last disconnected module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 20 | -- |
Did you record any DTCs which begin with a "U" and with a current status? | Go to Step 21 | ||
Did you record any DTCs which do not begin with a "U"? | Go to Step 22 | ||
22 | Use the scan tool in order to clear the DTCs. Did you complete the action? | System OK | -- |