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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2006 🢒 Escalade EXT 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 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 data link connector (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. • Audio Amplifier, w/UQ7 and Y91
    • Body Control Module (BCM)
    • CD Changer (CDX), w/U1S and Y91
    • Digital Radio Receiver (DRR), w/U2K or U2L
    • Driver Door Module (DDM)
    • Driver Seat Module (DSM), w/AN3
    • Electronic Brake Control Module (EBCM)
    • Electronic Suspension Control (ESC) Module, w/Z55
    • Front Passenger Door Module (FPDM)
    • Generator Battery Control Module (GBCM)
    • HVAC Control Module
    • HVAC Control Module - Rear Auxiliary
    • Instrument Panel Cluster (IPC)
    • Powertrain Control Module (PCM)
    • Radio
    • Rear Seat Audio (RSA) Controller, w/UK8
    • Rear Seat Entertainment (RSE) Assembly, w/U42
    • Rear Wheel Steering Control Module (RWSCM)
    • Inflatable Restraint Sensing and Diagnostic Module (SDM)
    • Transfer Case Shift Control Module (TCSCM), w/NP1/NP8
    • Vehicle Communication Interface Module (OnStar), w/UE1
    • Vehicle Theft Deterrent (VTD) Module, w/VD1

  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 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 or a short 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. This test isolates the BCM class 2 serial data circuits.

    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 splice pack SP207 serial data circuits.

    9.

  9. This test isolates the rest of the splice pack SP207 serial data circuits.

    10.

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

    11.

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

    12.

  12. 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

  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 30

Go to Step 6

6

Is U1000 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 Diagnostic System Check - Vehicle in DTC Vehicle Information

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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 Diagnostic System Check - Vehicle in DTC Vehicle Information

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 Diagnostic System Check - Vehicle in DTC Vehicle Information

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 Diagnostic System Check - Vehicle in DTC Vehicle Information

Go to Step 11

11

  1. Disconnect the theft deterrent control module, if equipped.
  2. Test the class 2 serial data circuits between the splice pack SP205 and DLC 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.
  3. Test the class 2 serial data circuits between the splice pack SP205 and theft deterrent control module, if equipped, 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 30

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 body control system (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 powertrain control module (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 30

Go to Step 28

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 30

Go to Step 28

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 30

--

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 30

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 30

Go to Step 23

21

  1. Disconnect the jumper wire from the splice pack SP207 terminal of the splice pack SP205 and connect it to the splice pack SP206 terminal of the splice pack SP205.
  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 26

Go to Step 22

22
  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 24

Go to Step 23

23

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 30

--

24

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 30

Go to Step 25

25
  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 SP206 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 30

Go to Step 28

26

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 splice pack SP207 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, one by one.
  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 30

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 30

Go to Step 28

28

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 30

Go to Step 29

29

Replace the last disconnected module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 30

--

30

  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?

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

Go to Step 31

31

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 32

32

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

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