GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Tahoe - 4WD 🢒 Body and Accessories 🢒 Instrument Panel, Gauges, and Console 🢒 Scan Tool Does Not Communicate with Class 2 Device

Circuit Description

Modules connected to the class 2 serial data circuit (some are optional) 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
    • The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must be connected to the DLC for any other module to communicate with the scan tool.
    • When the class 2 serial data circuit is shorted to ground, U1300 will be set. Refer to DTC U1300 .
    • When the class 2 serial data circuit is shorted to B+, U1301 will be set. Refer to DTC U1301 .

Test Description

  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. • Body Control Module (BCM)
    • Powertrain Control Module (PCM)
    • Automatic Transfer Case (ATC)
    • Electronic Brake Control Module (EBCM)
    • Inflatable Restraint Sensing and Diagnostic Module (SDM)
    • Instrument Panel Cluster (IPC)
    • Suspension Control Module (SCM)
    • HVAC Control Module
    • Automatic Transmission
    • Driver Information Center (DIC)
    • Memory Mirror Control Module
    • Memory Seat Control Module
    • OnStar® /Cellular Phone line

  1. The following DTCs may be retrieved with a history status:

    • U1300
    • U1301

These DTCs are not the cause of the present condition.

  1. A State of Health DTC with a history status may be present along with a U1000 or U1255 having a current status. This indicates that the malfunction occurred when the ignition was ON.

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

  1. A poor connection at terminal A would cause this condition but will not set a DTC.

  1. An open in the class 2 serial data circuit between the DLC and the star connector will prevent the scan tool from communicating with any module. This condition will not set a DTC.

  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 wiring for a short, make sure there is not a module connected to the wire being tested. This test isolates the BCM class 2 serial data circuit.

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

  1. This test isolates the ATC class 2 serial data circuit.

  1. This test isolates the EBCM class 2 serial data circuit.

  1. This test isolates the SDM class 2 serial data circuit.

  1. This test isolates the IPC class 2 serial data circuit.

  1. This test isolates the SCM class 2 serial data circuit.

  1. This test isolates the Automatic HVAC class 2 serial data circuit.

  1. This test isolates the Automatic Transmission class 2 serial data circuit.

  1. This test isolates the Driver Information Center (DIC) class 2 serial data circuit.

  1. This test isolates the Mirror Memory Module class 2 serial data circuit.

  1. This test isolates the Memory Seat Module class 2 serial data circuit.

  1. This test isolates the OnStar®/Cellular Phone class 2 serial data circuit.

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

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 leaving 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 7

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 models 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 in the range of U1000 to U1305?

Go to Step 4

Go to Diagnostic Aids

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 38

Go to Step 6

6

Is U1000 or U1255 the only DTC displayed in the previously specified range?

Go to DTC U1000 and U1255

Go to DTC U1001-U1254

7

  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 Control Module References for the applicable Diagnostic System Check

Go to Step 8

8

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 Control Module References for the applicable Diagnostic System Check

Go to Step 9

9

  1. Disconnect the star connector.
  2. Inspect for poor connections at the star connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References for the applicable Diagnostic System Check

Go to Step 10

10

Test the class 2 serial data circuit for an open or a short between the DLC and the star connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References for the applicable Diagnostic System Check

Go to Step 11

11

  1. Using the correct terminal adapter, connect a jumper wire to the DLC class 2 terminal of the star connector.
  2. Connect the other end of the jumper wire (with correct terminal adapter) to the BCM class 2 terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the BCM.

Does the scan tool communicate with the BCM?

Go to Step 13

Go to Step 12

12
  1. Turn OFF the ignition.
  2. Disconnect the BCM.
  3. Test the class 2 serial data circuit between the star connector and the BCM 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 complete the repair?

Go to Step 38

Go to Step 36

13

  1. Connect another jumper wire to the jumper wire connected to DLC class 2 terminal of the star connector.
  2. Connect the other end of the jumper wire (with correct terminal adapter) to the PCM class 2 terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the PCM.

Does the scan tool communicate with the PCM?

Go to Step 15

Go to Step 14

14
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Test the class 2 serial data circuit between the star connector 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 38

Go to Step 36

15

  1. Disconnect the jumper wire from the PCM circuit of the star connector.
  2. Connect the jumper wire to TCSCM class 2 circuit.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the TCSCM.

Does the scan tool communicate with the TCSCM?

Go to Step 17

Go to Step 16

16
  1. Turn OFF the ignition.
  2. Disconnect the TCSCM.
  3. Test the class 2 serial data circuit between the star connector and the TCSCM 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 38

Go to Step 36

17

  1. Disconnect the jumper wire from the TCSCM class 2 circuit of the star connector.
  2. Connect the jumper wire to the EBCM class 2 circuit of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the EBCM.

Does the scan tool communicate with the EBCM?

Go to Step 19

Go to Step 18

18
  1. Turn OFF the ignition.
  2. Disconnect the EBCM.
  3. Test the class 2 serial data circuit between the star connector and the EBCM 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 38

Go to Step 36

19

  1. Disconnect the jumper wire from the EBCM class 2 circuit of the star connector.
  2. Connect the jumper wire to the SDM class 2 circuit of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the SDM.

Does the scan tool communicate with the SDM?

Go to Step 21

Go to Step 20

20
  1. Turn OFF the ignition.
  2. Disconnect the SDM.
  3. Test the class 2 circuit between the star connector and the SDM 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 38

Go to Step 36

21

  1. Disconnect the jumper wire from the SDM class 2 circuit of the star connector.
  2. Connect the jumper wire to the IPC class 2 circuit of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the instrument panel cluster (IPC).

Does the scan tool communicate with the instrument panel cluster (IPC)?

Go to Step 23

Go to Step 22

22
  1. Turn OFF the ignition.
  2. Disconnect the instrument cluster (IPC).
  3. Test the IPC class 2 circuit between the star connector and the IPC 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 38

Go to Step 36

23

  1. Disconnect the jumper wire from the IPC class 2 circuit of the star connector.
  2. Connect the jumper wire to SCM class 2 circuit of the star connector.
  3. Attempt to communicate with the Suspension Control Module (SCM).

Does the scan tool communicate with the SCM?

Go to Step 25

Go to Step 24

24
  1. Turn off the ignition.
  2. Disconnect the SCM.
  3. Test the class 2 circuit between the star connector and the SCM 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 38

Go to Step 36

25

  1. Disconnect the jumper wire from the SCM class 2 circuit of the star connector.
  2. Connect the jumper wire to the HVAC class 2 circuit of the star connector.
  3. Attempt to communicate with the HVAC control module.

Does the scan tool communicate with the HVAC control module?

Go to Step 27

Go to Step 26

26
  1. Turn OFF the ignition.
  2. Disconnect the HVAC control module.
  3. Test the class 2 circuit between the star connector and the HVAC control 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 38

Go to Step 36

27

  1. Disconnect the jumper wire from the HVAC class 2 circuit of the star connector.
  2. Connect the jumper wire to the transmission class 2 circuit of the star connector.
  3. Attempt to communicate with the Transmission control module.

Does the scan tool communicate with the Transmission Module?

Go to Step 29

Go to Step 28

28
  1. Turn OFF the ignition.
  2. Disconnect the Transmission control module.
  3. Test the class 2 circuit between the star connector and the Transmission control 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 38

Go to Step 36

29

  1. Leave the jumper wire connected to terminal K of the star connector.
  2. Attempt to communicate with the DIC.

Does the scan tool communicate with the DIC?

Go to Step 31

Go to Step 30

30
  1. Turn OFF the ignition.
  2. Disconnect the DIC.
  3. Test the class 2 circuit between the star connector and the DIC 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 38

Go to Step 36

31

  1. Disconnect the jumper wire from terminal K of the star connector.
  2. Connect the jumper wire to the memory mirror/transfer case shift control module class 2 circuit of the star connector.
  3. Attempt to communicate with the memory Mirror Module (MMM).

Does the scan tool communicate with the MCM?

Go to Step 33

Go to Step 32

32
  1. Turn OFF the ignition.
  2. Disconnect the MMM.
  3. Test the class 2 circuit between the star connector and the MMM for 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 38

Go to Step 36

33

  1. Disconnect the jumper wire from the MMM class 2 circuit of the star connector.
  2. Connect the jumper wire to the MSM class 2 circuit of the star connector.
  3. Attempt to communicate with the MSM.

Does the scan tool communicate with the MSM?

Go to Step 35

Go to Step 34

34
  1. Turn OFF the ignition.
  2. Disconnect the MSM.
  3. Test the class 2 circuit between the star connector and the MSM 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 38

Go to Step 36

35

  1. Turn OFF the ignition.
  2. Test the class 2 circuit for the cellular phone ready wiring between the cellular phone communications class 2 circuit of star connector and the body wiring harness junction block 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 38

Go to Step 36

36

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 38

Go to Step 37

37

Replace the module which is not communicating. Refer to Control Module References for the appropriate repair instructions.

Did you complete the replacement?

Go to Step 38

--

38
  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. 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 40

Go to Step 39

39

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

Go to Step 40

Go to Step 42

40

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

Did you complete the action?

Go to Step 41

--

41

Did you diagnose all of the DTCs?

Go to Step 42

Go to Step 40

42

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK