GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2004 🢒 H2 🢒 Preface 🢒 Cautions and Notices 🢒 Scan Tool Does Not Communicate with Class 2 Device

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 Aids

The engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The following conditions will cause a total loss of class 2 serial data communication:

    • A class 2 serial data circuit shorted to ground.
    • A class 2 serial data circuit shorted to voltage.
    • An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit.

Test Description

The numbers below refer to the step numbers 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. • Air Suspension Module (ESC)
    • Audio Amplifier (early production), refer to Radio/Audio System Description and Operation in Entertainment for more information.
    • BCM
    • DDM
    • DSM
    • EBCM
    • FPDM
    • HVAC Control Module
    • IPC
    • PCM
    • Radio
    • RSA Module
    • SDM
    • TCSCM
    • VCIM

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

    3. • U1300
    • U1301
    • U1305

  3. A state of health DTC with a history status may be present along with a U1000 or U1255 code having a current status. This indicates that the malfunction occurred when the ignition was ON.

    4.

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

    5.

  5. A poor connection at DLC terminal of the splice pack - SP205 would cause this condition but will not set a DTC.

    6.

  6. An open in the class 2 serial data circuit between the DLC and splice pack - SP205 will prevent the scan tool from communicating with any module. This condition will not set a DTC.

    7.

  7. 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 BCM and the PCM class 2 serial data circuits.

    8.

  8. This test isolates the BCM class 2 serial data circuits.

    9.

  9. The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must remain connected to the DLC for any other module to communicate with the scan tool. This test isolates the splice pack - SP207 serial data circuits.

    10.

  10. This test isolates the splice pack - SP206 serial data circuits and radio.

    11.

  11. This test isolates the EBCM and TCSCM class 2 serial data circuits.

    12.

  12. This test isolates the rest of the splice pack - SP205 serial data circuits.

    13.

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

    14.

  14. 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 and Inline Harness Connector End Views in Wiring Systems

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 8

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 in the range of U1000 to U1305?

Go to Step 4

Go to Step 7

4

Are the history 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:

    •  Circuit Testing
    •  Connector Repairs
    •  Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 36

Go to Step 6

6

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

Go to DTC U1000

Go to DTC U1001-U1254

7

Diagnose the non-communicating module by using the DTC U1001-U1254 procedure for the module which is not communicating. Refer to DTC U1001-U1254

Did you complete the action?

Go to Control Module References in Body Control System for the applicable Diagnostic System Check

--

8
  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 in Body Control System for the applicable Diagnostic System Check

Go to Step 9

9

Test the DLC ground circuit at 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 in Body Control System for the applicable Diagnostic System Check

Go to Step 10

10

  1. Disconnect the splice pack - SP205.
  2. Inspect for poor connections at the splice pack - SP205. 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 in Body Control System for the applicable Diagnostic System Check

Go to Step 11

11

Test the class 2 serial data circuit between the DLC and the splice pack - SP205 for an open, 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 Control Module References in Body Control System for the applicable Diagnostic System Check

Go to Step 12

12

  1. Using the correct terminal adapter, connect a jumper wire to the DLC terminal of the splice pack - SP205.
  2. Connect the other end of the jumper wire, using correct terminal adapter, to the BCM terminal of the splice pack - SP205.
  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 16

Go to Step 13

13

  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  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 14

Go to Step 15

14
  1. Turn OFF the ignition.
  2. Test the class 2 serial data circuit between the splice pack - SP205 and the PCM for an open, 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 36

Go to Step 34

15
  1. Turn OFF the ignition.
  2. Disconnect the BCM.
  3. Test both class 2 serial data circuits of the BCM for an open, 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 36

Go to Step 34

16

  1. Leave the jumper wire connected to the DLC terminal and to the BCM terminal of the splice pack - SP205.
  2. Connect another jumper wire from the jumper wire connected to the DLC terminal of the splice pack - SP205.
  3. Connect the other end of the jumper wire, using correct terminal adapter, to the splice pack - SP207 terminal of the splice pack - SP205.
  4. Turn ON the ignition leaving the engine OFF.
  5. Attempt to communicate with the BCM.

Does the scan tool communicate with the BCM?

Go to Step 21

Go to Step 17

17
  1. Disconnect the splice pack - SP207.
  2. Inspect for poor connections at the splice pack - SP207. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
  3. Attempt to communicate with the BCM.

Does the scan tool communicate with the BCM?

Go to Step 19

Go to Step 18

18

Repair the class 2 serial data circuit for a short to ground or a short to voltage between the splice pack - SP205 and the splice pack - SP207. 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 36

--

19

Repeat the following steps on the class  2 serial data circuits connected to the splice pack - SP207 until the concern is located:

  1. Connect another jumper wire to the splice pack - SP205 terminal of the splice pack - SP207.
  2. Connect the other end of the jumper wire, using correct terminal adapter, to the terminal for the devices connected to splice pack - SP207.
  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 36

Go to Step 20

20
  1. Turn OFF the ignition.
  2. Disconnect the module that caused the no communication condition.
  3. Test the class 2 serial data circuit between the splice pack - SP207 and the respective 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 36

Go to Step 34

21

  1. Disconnect the jumper wire from the splice pack - SP207 terminal of the splice pack - SP205.
  2. Connect the jumper wire to the splice pack - SP206 terminal of the splice pack - SP205.
  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 28

Go to Step 22

22
  1. Turn OFF the ignition.
  2. Disconnect the radio.
  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 34

Go to Step 23

23

Test the class 2 serial data circuit between the splice pack - SP205 and the radio 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 the condition?

Go to Step 36

Go to Step 24

24
  1. Disconnect the splice pack - SP206.
  2. Inspect for poor connections at the splice pack - SP206. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
  3. Attempt to communicate with the BCM.

Does the scan tool communicate with the BCM?

Go to Step 26

Go to Step 25

25

Repair the class 2 serial data circuit for a short to ground or a short to voltage between the splice pack - SP205 and the splice pack - SP206. 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 36

--

26

Repeat the following steps on the class 2 serial data circuits connected to the splice pack - SP206 until the concern is located:

  1. Connect another jumper wire to the splice pack - SP205 terminal of the splice pack - SP206.
  2. Connect the other end of the jumper wire, using correct terminal adapter, to the terminal for the devices connected to splice pack - SP206.
  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 36

Go to Step 27

27
  1. Turn OFF the ignition.
  2. Disconnect the module that caused the no communication condition.
  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 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 36

Go to Step 34

28

  1. Disconnect the jumper wire from the splice pack - SP206 terminal of the splice pack - SP205.
  2. Connect the jumper wire to the EBCM terminal of the splice pack - SP205.
  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 32

Go to Step 29

29
  1. Turn OFF the ignition.
  2. Disconnect the EBCM.
  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 34

Go to Step 30

30
  1. Turn OFF the ignition.
  2. Disconnect the TCSCM.
  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 34

Go to Step 31

31

Repair the class 2 serial data circuit between the splice pack - SP205 and either the EBCM or 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 complete the repair?

Go to Step 36

--

32

Repeat the following steps on the class 2 serial data circuits connected to the splice pack - SP205 until the concern is located:

  1. Disconnect the jumper wire from the EBCM terminal of the splice pack - SP205.
  2. Connect the jumper wire, using correct terminal adapter, to the terminal for the rest of devices connected to splice pack - SP205.
  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 36

Go to Step 33

33
  1. Turn OFF the ignition.
  2. Disconnect the module that caused the no communication condition.
  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 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 36

Go to Step 34

34

Inspect for poor connections at the class 2 serial data circuit of the last disconnected module. 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 36

Go to Step 35

35

Important: Perform the module setup procedure if required.

Replace the last disconnected module. Refer to Control Module References in Body Control System for the appropriate repair instructions.

Did you complete the replacement?

Go to Step 36

--

36

  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?

Go to Step 38

Go to Step 37

37

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

Go to Step 38

Go to Step 40

38

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

Did you complete the action?

Go to Step 39

--

39

Did you diagnose all of the DTCs?

Go to Step 40

Go to Step 38

40

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--