GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 SSR 🢒 Restraints 🢒 SIR 🢒 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.

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 DTC
    • 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 DTC
    • 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 DTC Sets
    • 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.

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 engine control module (ECM) only, because ECM functionally communicates on both class 2 and high speed GMLAN 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.

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 SP300 serial data circuits, if equipped.

    2.

  2. This test isolates the splice pack SP201 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 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

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 in Wiring Systems:

    •  Circuit Testing
    •  Connector Repairs
    •  Wiring Repairs

Did you find and correct the condition?

Go to Step 21

--

4
  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM).
  3. Turn ON the ignition.
  4. Attempt to communicate with the body control module (BCM).

Does the scan tool communicate with BCM?

Go to Step 17

Go to Step 5

5

Important: If the vehicle doesn't have splice pack SP300 skip to step 8.

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

Did you record U1300 or U1301, as current?

Go to Step 8

Go to Step 6

6

Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP300 until the concern is located:

  1. Turn OFF the ignition.
  2. Using the correct terminal adapter, connect a jumper wire to the splice pack SP201 terminal of the splice pack SP300.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the terminal for the devices connected to splice pack SP300.
  4. Turn ON the ignition, with the engine OFF.
  5. Retrieve the DTCs from the ECM.

Did you record U1300 or U1301, as current?

Go to Step 7

Go to Testing for Intermittent Conditions and Poor Connections

7
  1. Turn OFF the ignition.
  2. Disconnect the module that caused the DTC to be set.
  3. Test the class 2 serial data circuit between the splice pack SP300 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 19

Go to Step 17

8
  1. Turn OFF the ignition.
  2. Reconnect the ECM if not previously reconnected.
  3. Disconnect the splice pack SP201.
  4. Turn ON the ignition, with the engine OFF.
  5. Retrieve DTCs from ECM.

Did you record U1300 or U1301, as current?

Go to Step 9

Go to Step 13

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

Did you record U1300 or U1301, as current?

Go to Step 11

Go to Step 10

10
  1. Turn OFF the ignition.
  2. Test the class 2 serial data circuits between BCM and splice pack SP201 for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 19

Go to Step 17

11
  1. Turn OFF the ignition.
  2. Disconnect the transmission control module (TCM).
  3. Turn ON the ignition, with the engine OFF.
  4. Retrieve DTCs from ECM.

Did you record U1300 or U1301, as current?

Go to Step 12

Go to Step 17

12
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Test all class 2 serial data circuits of the ECM 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 19

--

13

Important: If the vehicle doesn't have splice pack SP300 skip to step 15.

  1. Turn OFF the ignition.
  2. Using the correct terminal adapter, connect a jumper wire to the ECM terminal of the splice pack SP201.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the splice pack SP300 terminal of the splice pack SP201.
  4. Turn ON the ignition, with the engine OFF.
  5. Retrieve DTCs from ECM.

Did you record U1300 or U1301, as current?

Go to Step 14

Go to Step 15

14
  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 SP201 and the splice pack SP300. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 19

--

15

Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP201 until the concern is located:

  1. Turn OFF the ignition.
  2. Using the correct terminal adapter, connect a jumper wire to the ECM terminal of the splice pack SP201, if not previously connected.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the terminal for the devices connected to splice pack SP201.
  4. Turn ON the ignition, with the engine OFF.
  5. Retrieve DTCs from ECM.

Did you record U1300 or U1301, as current?

Go to Step 16

Go to Testing for Intermittent Conditions and Poor Connections

16
  1. Turn OFF the ignition.
  2. Disconnect the module that caused the DTC to be set.
  3. Test the class 2 serial data circuit between the splice pack SP201 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 19

Go to Step 17

17

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 19

Go to Step 18

18

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

Did you complete the replacement?

Go to Step 19

--

19

  1. Reconnect all of the disconnected modules and splice packs.
  2. Install a scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. Retrieve the DTCs.

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 20

20

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

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 21

21

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

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