GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 XLR 🢒 Power and Signal Distribution 🢒 Data Communications 🢒 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

DTC Symptom

DTC Symptom Descriptor

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

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

The numbers below refer to the step numbers on the diagnostic table.

  1. 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.

    2.

  2. This test isolates the splice pack SP208 serial data circuits.

    3.

  3. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.

    4.

  4. 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

Go to Diagnostic System Check - Vehicle

2
  1. Turn ON the ignition, with the engine OFF.
  2. Retrieve DTCs from body control module (BCM).

Did you record U1305, 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:

    •  Circuit Testing
    •  Connector Repairs
    •  Wiring Repairs

Did you find and correct the condition?

Go to Step 19

--

4
  1. Turn OFF the ignition.
  2. Disconnect the splice pack SP205.
  3. Turn ON the ignition, with the engine OFF.
  4. Retrieve DTCs from BCM.

Did you record U1305, as current?

Go to Step 9

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Using the correct terminal adapter, connect a jumper wire to the splice pack SP208 terminal of the splice pack SP205.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the data link connector (DLC) terminal of the splice pack SP205.
  4. Turn ON the ignition, with the engine OFF.
  5. Retrieve DTCs from BCM.

Did you record U1305, as current?

Go to Step 6

Go to Step 7

6
  1. Turn OFF the ignition.
  2. Repair the short in the class 2 serial data circuit between the DLC and the splice pack SP205. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

--

7

Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP205 until the concern is located:

  1. Turn OFF the ignition.
  2. Leave the jumper wire connected to the splice pack SP208 terminal of the splice pack SP205.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the terminal for the devices connected to splice pack SP205.
  4. Turn ON the ignition, with the engine OFF.
  5. Retrieve DTCs from BCM.

Did you record U1305, as current?

Go to Step 8

Go to Step 16

8
  1. Turn OFF the ignition.
  2. Disconnect the module that caused the no communication condition.
  3. Test the class 2 serial data circuit between the splice pack SP205 and the respective module for a short to ground or a short to voltage. Turn ON the ignition, with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 16

Go to Step 15

9
  1. Turn OFF the ignition.
  2. Disconnect the splice pack SP208.
  3. Turn ON the ignition, with the engine OFF.
  4. Retrieve DTCs from BCM.

Did you record U1305, as current?

Go to Step 10

Go to Step 11

10
  1. Turn OFF the ignition.
  2. Disconnect the BCM.
  3. Test the class 2 serial data circuit between the splice pack SP208 and the BCM for a short to ground or a short to voltage. Turn ON the ignition, with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 16

Go to Step 15

11
  1. Turn OFF the ignition.
  2. Using the correct terminal adapter, connect a jumper wire to the BCM terminal of the splice pack SP208.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the splice pack SP205 terminal of the splice pack SP208.
  4. Turn ON the ignition, with the engine OFF.
  5. Retrieve DTCs from BCM.

Did you record U1305, as current?

Go to Step 12

Go to Step 13

12
  1. Turn OFF the ignition.
  2. Repair the short to ground or short to voltage in the class 2 serial data circuit between the splice pack SP205 and the splice pack SP208. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

--

13

Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP208 until the concern is located:

  1. Turn OFF the ignition.
  2. Leave the jumper wire connected to the BCM terminal of the splice pack SP208.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the terminal for the devices connected to splice pack SP208.
  4. Turn ON the ignition, with the engine OFF.
  5. Retrieve DTCs from BCM.

Did you record U1305, as current?

Go to Step 14

Go to Step 16

14
  1. Turn OFF the ignition.
  2. Disconnect the module that caused the no communication condition.
  3. Test the class 2 serial data circuit between the splice pack SP208 and the respective module for a short to ground or a short to voltage. Turn ON the ignition, with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 16

Go to Step 15

15

Replace the last disconnected module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 16

--

16

  1. Reconnect all of the disconnected modules.
  2. Reconnect any other disconnected connectors.
  3. Install a scan tool.
  4. Turn ON the ignition, with the engine OFF.
  5. Retrieve DTCs using Vehicle DTC Information feature on the scan tool, under Computer/Integrating System menu.

Did you record any DTCs which begin with a "U" and with a current status?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 17

17

Did you record any DTCs which do not begin with a "U"?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 18

18

Did you diagnose all of the DTCs?

Go to Step 19

Go to Step 16

19

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

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