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Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C-Series Medium Duty Truck B7 🢒 Body and Accessories 🢒 Instrument Panel, Gauges, and Console 🢒 Scan Tool Does Not Communicate with Class 2 Device

Scan Tool Does Not Communicate with Class 2 Device 8.1 L18 Gas

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. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes. Diagnostic trouble codes (DTCs) may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.

Diagnostic Aids
    • When the class 2 serial data circuit is shorted to ground, DTC U1300 will be set. Refer to DTC U1300 .
    • When the class 2 serial data circuit is shorted to B+, DTC U1301 will be set. Refer to DTC U1301 .

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit. The following modules communicate on the class 2 serial data circuit:

    2. • The Powertrain Control Module (PCM)
    • The Transmission Control Module (TCM)

  2. The following DTCs may be retrieved with a history status, but are not the cause of the present condition.

    3. • U1300
    • U1301

  3. Data link connector terminal 2 and terminal 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.

    4.

  4. This test isolates the PCM class 2 serial data circuit.

    5.

  5. This test isolates the internal PCM circuit that connects the two external class 2 serial data circuits together.

    6.

  6. This test isolates the TCM class 2 serial data circuit.

    7.

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

    8.

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

Step

Action

Yes

No

Schematic Reference: Data Link Connector Schematics

1

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not Power Up

2

  1. Turn ON the ignition with the engine OFF.
  2. Attempt to communicate with each module on the class 2 serial data circuit. (If using a Tech 2, obtain this information using the Class 2 Message Monitor feature.)

Does the scan tool communicate with any module on the Class 2 serial data circuit?

Go to Step 3

Go to Step 6

3

  1. 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.)
  2. Record all of the displayed DTCs, the DTC status and the module which set the DTC.

Did you record any DTCs that apply to other modules?

Go to the applicable Diagnostic System Check

Go to Step 6

4

Are the DTCs U1300, U1301 or U1305 retrieved from any module?

Go to Step 5

Go to Step 6

5

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

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Disconnect the scan tool from the data link connector (DLC).
  3. Inspect for poor connections at the DLC terminals 2 and 5. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 7

7

Test the DLC ground circuit terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 8

8

  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Test the class 2 serial data circuit between the DLC and the PCM 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 9

9

  1. Connect the jumper wire between the class 2 serial data circuits of the PCM.
  2. Turn ON the ignition leaving the engine OFF.
  3. Attempt to communicate with the Transmission Control Module (TCM).

Does the scan tool communicate with the TCM?

Go to Step 11

Go to Step 10

10

  1. Turn OFF the ignition.
  2. Disconnect the TCM.
  3. Test the class 2 serial data circuit between the TCM and the PCM 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 14

Go to Step 12

11

Replace the PCM. Refer to Powertrain Control Module Replacement in 8.1 Engine Controls.

Is the replacement complete?

Go to Step 15

--

12

Inspect for poor connections at the class 2 serial data circuit of the module that is not communicating. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 13

13

Replace the module which is not communicating. Refer to the appropriate repair instructions.

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 or disconnect 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?

Go to Step 16

Go to Step 15

15

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

Go to Step 16

Go to Step 17

16

Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Refer to the applicable Diagnostic System Check.

Did you complete the action?

Go to Step 17

--

17

Did you diagnose all of the DTCs?

Go to Step 18

Go to Step 16

18

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--

Scan Tool Does Not Communicate with Class 2 Device 7.2 LG5 Diesel

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. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes. Diagnostic trouble codes (DTCs) may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.

Diagnostic Aids
    • When the class 2 serial data circuit is shorted to ground, DTC U1300 will be set. Refer to DTC U1300 .
    • When the class 2 serial data circuit is shorted to B+, DTC U1301 will be set. Refer to DTC U1301 .

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. The (Allison) transmission control module communicates on the class 2 serial data circuit.

    2.

  2. The following DTCs may be retrieved with a history status, but are not the cause of the present condition.

    3. • U1300
    • U1301

  3. Data link connector terminal 2 and terminal 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.

    4.

  4. This test isolates the TCM class 2 serial data circuit.

    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

1

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not Power Up

2

  1. Turn ON the ignition with the engine OFF.
  2. Attempt to communicate with the transmission control module (TCM) on the class 2 serial data circuit. (If using a Tech 2, obtain this information using the Class 2 Message Monitor feature.)

Does the scan tool communicate with the TCM on the Class 2 serial data circuit?

Go to Step 3

Go to Step 6

3

  1. 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.)
  2. Record all of the displayed DTCs, the DTC status and the module which set the DTC.

Did you record any DTCs that apply to other modules?

Go to the applicable Diagnostic System Check

Go to Step 6

4

Are the DTCs U1300, U1301 or U1305 retrieved from any module?

Go to Step 5

Go to Step 6

5

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 10

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Disconnect the scan tool from the data link connector (DLC).
  3. Inspect for poor connections at the DLC terminals 2 and 5. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 7

7

Test the DLC ground circuit terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 8

8

  1. Turn OFF the ignition.
  2. Disconnect the TCM.
  3. Test the class 2 serial data circuit between the TCM and the DLC 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 9

9

Replace the TCM. Refer to the appropriate repair instructions.

Did you complete the replacement?

Go to Step 10

--

10

  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 or disconnect 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?

Go to Step 12

Go to Step 11

11

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

Go to Step 12

Go to Step 13

12

Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Refer to the applicable Diagnostic System Check.

Did you complete the action?

Go to Step 13

--

13

Did you diagnose all of the DTCs?

Go to Step 14

Go to Step 12

14

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--