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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Envoy - 4WD 🢒 Body and Accessories 🢒 Theft Deterrent 🢒 Scan Tool Does Not Communicate with Class 2 Device

Circuit Description

Modules connected to the class 2 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. 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 circuit is shorted to battery negative voltage, U1300 will be set. Refer to DTC U1300 .
    • When the class 2 circuit is shorted to battery positive voltage U1301 will be set. Refer to DTC U1301 .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

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

    2. • Electronic climate control module (ECCM)
    • Transfer case shift control module (TCSCM)
    • Electronic brake control module (EBCM)
    • Powertrain control module (PCM)
    • Vehicle interface unit (VIU)
    • Body control module (BCM)
    • Instrument panel cluster (IPC)
    • Driver information center (DIC)
    • Memory seat module (MSM)
    • Inflatable restraint sensing and diagnostic module (SDM)

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

    3. • U1300
    • U1301

  3. 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.

    4.

  4. DLC 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 terminal A would cause this condition but will not set a DTC.

    6.

  6. An open in the class 2 circuit between the DLC and SP201 will prevent the scan tool from communicating with a module. This condition will not set a DTC.

    7.

  7. The class 2 circuit is shorted to battery positive voltage or battery negative voltage. 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 class 2 circuit.

    8.

  8. 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 PCM class 2 circuit.

    9.

  9. This test isolates the TCSCM class 2 circuit.

    10.

  10. This test isolates the VIU class 2 circuit.

    11.

  11. This test isolates the EBCM class 2 circuit.

    12.

  12. This test isolates the SDM class 2 circuit.

    13.

  13. This test isolates the IPC class 2 circuit.

    14.

  14. This test isolates the MSM class 2 circuit.

    15.

  15. This test isolates the DIC class 2 circuit.

    16.

  16. This test isolates the ECCM class 2 circuit.

    17.

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

    18.

  18. 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 leaving the engine OFF.
  2. Attempt to communicate with each module on the class 2 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 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 6

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 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 33

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. Remove the scan tool from the DLC.
  3. Inspect for poor connections at the DLC ground terminals. 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 Systems for the applicable Diagnostic System Check

Go to Step 8

8

Test the DLC signal return circuit 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 Systems for the applicable Diagnostic System Check

Go to Step 9

9

  1. Remove the comb SP201.
  2. Inspect for poor connections at SP201. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
  3. Test for continuity between pin A and all other pins at SP201. 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 Systems for the applicable Diagnostic System Check

Go to Step 10

10

Test the DLC class 2 circuit for an open or a short. 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 Systems for the applicable Diagnostic System Check

Go to Step 11

11

  1. Connect a jumper wire to each end of both BCM class 2 serial data circuits.
  2. Turn ON the ignition leaving the engine OFF.
  3. 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. Remove C1 and C2 of the BCM.
  3. Test the BCM class 2 circuits for a short to battery negative voltage or a short to battery positive voltage. Turn ON the ignition leaving the engine OFF when testing for a short to battery negative voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 33

Go to Step 31

13

  1. Leave the jumper wires connected to the BCM class 2 circuit.
  2. Connect another jumper wire to each end of the PCM class 2 circuit.
  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. Remove C1 of the PCM.
  3. Test the PCM class 2 circuit for a short to battery negative voltage or a short to battery positive 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 33

Go to Step 31

15

  1. Remove the jumper wire from the PCM class 2 circuit.
  2. Connect the jumper wire to the end of the 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. Remove the connector which contains the TCSCM class 2 circuit.
  3. Test the TCSCM class 2 circuit for a short to battery negative voltage or a short to battery positive 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 33

Go to Step 31

17

  1. Remove the jumper wire from the TCSCM class 2 circuit.
  2. Connect the jumper wire to the end of the VIU class 2 circuit.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the VIU.

Does the scan tool communicate with the VIU?

Go to Step 19

Go to Step 18

18
  1. Turn OFF the ignition.
  2. Remove the VIU connector.
  3. Test the VIU class 2 circuit for a short to battery negative voltage or a short to battery positive 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 33

Go to Step 31

19

  1. Remove the jumper wire from the VIU class 2 circuit.
  2. Connect the jumper wire to the end of the EBCM class 2 circuit.
  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 21

Go to Step 20

20
  1. Turn OFF the ignition.
  2. Remove C1 of the EBCM.
  3. Test the EBCM class 2 circuit for a short to battery negative voltage or a short to battery positive voltage. Turn ON the ignition leaving the engine OFF when testing for a short to batery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 33

Go to Step 31

21

  1. Remove the jumper wire from the EBCM class 2 circuit.
  2. Connect the jumper wire to the end of the SDM class 2 circuit..
  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 23

Go to Step 22

22
  1. Turn OFF the ignition.
  2. Remove the SDM connector.
  3. Test the SDM class 2 circuit for a short to battery negative voltage or a short to battery positive 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 System.

Did you find and correct the condition?

Go to Step 33

Go to Step 31

23

  1. Remove the jumper wire from the SDM class 2 circuit.
  2. Connect the jumper wire to the end of the IPC class 2 circuit.
  3. Turn ON the ignition leaving the engine OFF.

    4. Attempt to communicate with the IPC.

Does the scan tool communicate with the IPC?

Go to Step 25

Go to Step 24

24
  1. Turn OFF the ignition.
  2. Remove the IPC connector.
  3. Test the IPC class 2 circuit for a short to battery negative voltage or a short to battery positive voltage. Turn ON the ignition leaving the engine OFF when testing for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 33

Go to Step 31

25

  1. Remove the jumper wire from the IPC class 2 circuit.
  2. Connect the jumper wire to the end of the MSM.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the MSM.

Does the scan tool communicate with the MSM?

Go to Step 27

Go to Step 26

26
  1. Turn OFF the ignition.
  2. Remove C1 of the MSM.
  3. Test the MSM class 2 circuit for a short to battery negative voltage or a short to battery positive voltage. Turn ON the ignition leaving the engine OFF when testing for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 33

Go to Step 31

27

  1. Remove the jumper wire from the MSM class 2 circuit.
  2. Connect the jumper wire to the end of the DIC.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the DIC.

Does the scan tool communicate with the DIC?

Go to Step 33

Go to Step 28

28
  1. Turn OFF the ignition.
  2. Remove C1 of the DIC.
  3. Test the DIC class 2 circuit for a short to battery negative voltage or a short to battery positive voltage. Turn ON the ignition leaving the engine OFF when testing for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 33

Go to Step 29

29

  1. Remove the jumper wire from the DIC class 2 circuit.
  2. Connect the jumper wire to the end of the ECCM.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the ECCM.

Does the scan tool communicate with the ECCM?

Go to Step 33

Go to Step 30

30
  1. Turn OFF the ignition.
  2. Remove the ECCM connector.
  3. Test the ECCM class 2 circuit for a short to battery negative voltage or a short to battery positive voltage. Turn ON the ignition leaving the engine OFF when testing for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 33

Go to Step 31

31

Inspect for poor connections at the class 2 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 33

Go to Step 32

32

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

Did you complete the replacement?

Go to Step 33

--

33

  1. Connect all of the modules.
  2. Connect any other connectors.
  3. Connect 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 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 35

Go to Step 34

34

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

Go to Step 35

Go to Step 37

35

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

Did you complete the action?

Go to Step 36

--

36

Did you diagnose all of the DTCs?

Go to Step 37

Go to Step 35

37

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--