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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 DeVille 🢒 Brakes 🢒 Antilock Brake System 🢒 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 malfunction of the class 2 serial data circuit while the engine is not running.

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.

    2.

  2. The following DTCs may be retrieved with a history status. These DTCs 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 with a current status. This indicates that the malfunction occurred when the ignition was on.

    4.

  4. The following modules are not monitored by other modules:

    5. • Left Middle Door Module (LMDM)
    • Memory Seat Module (MSM)
    • Navigation Data Entry Processor
    • Rear Heater and A/C Control (w/o B9Q)
    • Right Middle Door Module (RMDM)
    • Steering Column Module

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

    6.

  6. An open in the class 2 serial data circuit between the DLC and splice C200 will prevent the scan tool from communicating with any module. This condition will not set a DTC.

    7.

  7. If communication can be established, the malfunction is located in the wiring or one of the modules connected to splice pack SP300.

    8.

  8. If communication can be established, the malfunction is located in the wiring or one of the modules connected to splice pack SP304.

    9.

  9. If communication can be established, the fault is in the wiring or one of the modules between C200 and SP300.

    10.

  10. If communication can be established, the malfunction is in the wiring or one of the modules between the instrument cluster (IPC) and the dash integration module (DIM).

    11.

  11. If there are no current DTCs that begin with the letter 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

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 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 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 27

Go to Step 6

6

Are U1000 and U1255 the only DTCs displayed in the previously specified range?

Go to DTC U1000 and DTC U1255 Class 2 Communication Malfunction

Go to DTC U1001-U1254 Loss of XXX Communications

7

Diagnose the malfunction using the DTC U1001--U1254 Loss of XXX Communications procedures for the module which is not communicating. Refer to DTC U1001-U1254 Loss of XXX Communications .

Did you complete the action?

Go to Control Module References 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. 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 7

9

Test the ground circuit of the DLC 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 8

10

Test the class 2 serial data circuit of the DLC 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

11

  1. Turn OFF the ignition.
  2. Disconnect the splice pack SP300.
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit.

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

Go to Step 16

Go to Step 10

12

  1. Turn OFF the ignition.
  2. Disconnect splice pack SP304.
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit.

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

Go to Step 17

Go to Step 11

13

  1. Turn OFF the ignition.
  2. Disconnect C200.
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit.

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

Go to Step 18

Go to Step 12

14

  1. Turn OFF the ignition.
  2. Disconnect the DIM.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the class 2 serial data circuit between SP304 and the DIM for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 13

15
  1. Turn OFF the ignition.
  2. Disconnect the IPM.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the class 2 serial data circuit between the IPM and the DIM for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 14

16

  1. Turn OFF the ignition.
  2. Connect C200
  3. Connect SP300.
  4. Connect SP304.
  5. Connect the DIM.
  6. Disconnect the IPC.
  7. Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit.

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

Go to Step 22

Go to Step 23

17

  1. Turn OFF the ignition.
  2. Disconnect all the modules between the DIM and C200.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the class 2 serial data circuit between the DIM and C200 for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 19

18

  1. Turn OFF the ignition.
  2. Disconnect all the modules connected to SP300.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the class 2 serial data circuit between SP300 and the disconnected modules for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 19

19
  1. Turn OFF the ignition.
  2. Disconnect all the modules connected to SP304.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the class 2 serial data circuit between SP304 and all the disconnected modules for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 19

20

  1. Turn OFF the ignition.
  2. Disconnect all the modules between C200 and SP300.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the class 2 serial data circuit between C200 and SP300 for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 19

21
  1. Turn OFF the ignition.
  2. Connect the one of the modules in the suspect area.
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit.

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

Go to Step 20

Go to Step 21

22

Continue connecting the modules in the suspect area one at a time. Attempt to communicate after each connection until communication cannot be established or all the modules are connected.

Did you find the condition?

Go to Step 21

Go to Testing for Electrical Intermittents in Wiring Systems

23

Inspect for poor connections/terminal tension at the class 2 serial data circuit of the most recently connected 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 25

Go to Step 22

24

Replace the most recently disconnected or reconnected module. Refer to Control Module References for the appropriate Repair Instructions for module replacement.

Did you complete the replacement?

Go to Step 25

--

25

  1. Turn ON the ignition, with the engine OFF.
  2. Test the class 2 serial data circuit between the IPC and C200 for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 24

26

Replace the DIM. Refer to Control Module References for the appropriate Repair Instructions for module replacement.

Did you complete the replacement?

Go to Step 25

--

27

  1. Connect all of the modules.
  2. Connect all the connectors.
  3. Install a scan tool.
  4. Turn ON the ignition leaving the engine OFF.

    5. Important: 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 before you display DTCs.

  5. Wait for 10 seconds.
  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 your record any DTCs which begin with a U and with a current status?

Go to Step 27

Go to Step 26

28

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

Go to Step 27

Go to Step 28

29

Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction.

Did you complete the action?

Go to Step 28

--

30

Did you diagnose all of the DTCs?

Go to Step 29

Go to Step 27

31

Clear the DTCs using the scan tool.

Did you complete the action?

System OK

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