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For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2006 🢒 Ascender - 2WD 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 DTC U1300, U1301, or U1305

DTC U1300, U1301, or U1305 5.3L

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

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 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.

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 SP306 serial data circuits.

    2.

  2. This test isolates the splice pack SP205 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 in Wiring Systems

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

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 22

--

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 18

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Reconnect the ECM.
  3. Disconnect the splice pack SP306.
  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 SP306 until the concern is located:

  1. Turn OFF the ignition.
  2. Using the correct terminal adapter, connect a jumper wire to the splice pack SP205 terminal of the splice pack SP306.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the terminal for the devices connected to splice pack SP306.
  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 in Wiring Systems

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 SP306 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 18

8
  1. Turn OFF the ignition.
  2. Disconnect the splice pack SP205.
  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 9

Go to Step 12

9
  1. Turn OFF the ignition.
  2. Disconnect the theft deterrent control module (VTD), if equipped, or disconnect the BCM, if not equipped with VTD.
  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 circuit between VTD, if equipped, or BCM if not equipped with VTD, and splice pack SP205 for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 16

11
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Test the class 2 serial data circuit between the ECM and VTD, if equipped, or BCM if not equipped with VTD, 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 in Wiring Systems.
  4. Test the class 2 serial data circuit between the ECM and splice pack SP306 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 16

12
  1. Turn OFF the ignition.
  2. Using the correct terminal adapter, connect a jumper wire to the ECM terminal of the splice pack SP205.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the splice pack SP306 terminal of the splice pack SP205.
  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 13

Go to Step 14

13
  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 SP306. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

--

14

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 ECM 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 ECM.

Did you record U1300 or U1301, as current?

Go to Step 15

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

15
  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 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 in Wiring Systems.

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 in Wiring Systems.

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 in Wiring Systems.

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

--

20

  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 in Vehicle DTC Information

Go to Step 21

21

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

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 22

22

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--

DTC U1300, U1301, or U1305 4.2L

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

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.

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 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 .