GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 SRX 🢒 DTC 🢒 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

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

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

  1. This step takes out from the class 2 bus the modules connected to splice pack SP304.

    2.

  2. This step takes out from the class 2 bus the modules connected to splice pack SP300.

    3.

  3. This step takes out from the class 2 bus the modules connected to splice pack SP200.

    4.

  4. This test localizes the short on the rest of modules/circuits still connected to class 2 circuits of the ECM.

    5.

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

    6.

  6. The communication malfunction may have prevented diagnosis of the customer complaint.

Step

Action

Yes

No

Schematic Reference: Data Link Connector 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 engine control module (ECM).

Did you record DTC 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 in Wiring Systems:

    •  Circuit Testing
    •  Connector Repairs
    •  Wiring Repairs

Did you find and correct the condition?

Go to Step 14

--

4

  1. Turn OFF the ignition.
  2. Disconnect the splice pack SP304.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Retrieve DTCs from ECM.

Did you record DTC U1300 or U1301, as current?

Go to Step 5

Go to Step 10

5

  1. Turn OFF the ignition.
  2. Disconnect the splice pack SP300.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Retrieve DTCs from ECM.

Did you record DTC U1300 or U1301, as current?

Go to Step 6

Go to Step 10

6

  1. Turn OFF the ignition.
  2. Disconnect the splice pack SP200.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Retrieve DTCs from ECM.

Did you record DTC U1300 or U1301, as current?

Go to Step 7

Go to Step 10

7

Important: Repeat this step until condition disappears or all required modules were disconnected.

  1. Turn OFF the ignition.
  2. Disconnect the farthest module from the ECM that is still connected to class 2 serial data circuits.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Retrieve DTCs from ECM.

Did you record DTC U1300 or U1301, as current?

Go to Step 8

Go to Step 9

8
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Test the class 2 serial data circuits of the ECM for a short to ground or a short to voltage. Turn ON the ignition, leaving 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 14

Go to Step 12

9
  1. Turn OFF the ignition.
  2. Test the class 2 serial data circuits of the disconnected module for a short to ground or a short to voltage. Turn ON the ignition, leaving 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 14

Go to Step 12

10

Using the appropriate jumper at the suspected splice pack, perform the following in order to determine which class 2 serial data circuit or module is causing the concern:

  1. Turn ON the ignition, with the engine OFF.
  2. Retrieve DTCs from ECM.
  3. Connect each module of the respective splice pack to the class 2 serial data circuit one at a time until DTC U1300 or U1301 is set as current.

Did you complete the action?

Go to Step 11

--

11

Test the class 2 serial data circuits of the suspected module for a short to ground or a short to voltage. Turn ON the ignition, leaving 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 14

Go to Step 12

12

Inspect for poor connections at the class 2 serial data circuit of the suspected module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 13

13

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

Did you complete the replacement?

Go to Step 14

--

14

  1. Reconnect all of the disconnected modules.
  2. Reconnect any other disconnected connectors.
  3. Install a scan tool.
  4. Turn ON the ignition, leaving the engine OFF.
  5. Wait for 10 seconds.

    6. The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn OFF the scan tool prior to performing this test.

  6. Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
  7. Record all of the displayed DTCs and the DTC status.

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

Refer to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 15

15

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

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 16

16

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

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