GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Firebird 🢒 Body and Accessories 🢒 Data Link Communications 🢒 Scan Tool Does Not Communicate with Class 2 Data Line

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.

The diagnostic procedure assumes that all modules are powered. When you are uncertain whether this condition is met, perform the Diagnostic System Check for the module in question. 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
    • Use a J35616-A when probing or checking electrical connector terminals. The J35616-A prevents terminal damage, plus checks for proper terminal contact tension.
    • If a short to B+ is present a history U1301 will set in the modules. Refer to DTC U1301 Class 2 Short to Battery .
    • If a short to ground is present a history U1300 will set in the modules. Refer to DTC U1300 Class 2 Short to Ground .
    • If the malfunction is intermittent refer to Intermittents and Poor Connections Diagnosis .
    • Disconnecting modules and turning the ignition switch to RUN may cause DTCs in these modules. Check for DTCs in each module upon completion of the required repair.
    • Make sure the theft deterrent system has not caused a class 2 no communication malfunction. Refer to Vehicle Theft Deterrent (VTD) System Check .

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.

    2.

  2. DTCs U1300 and/or U1301 may be retrieved with a history status. These DTCs are not the cause of the present condition.

    3.

  3. A state of health DTC with a history status may be present along with a U1000 having a current status. This indicates the malfunction occured 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 terminal G 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 star connector 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 wiring for a short, make sure there is not a module connected to the wire being tested. This test isolates the PCM class 2 serial data circuit.

    8.

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

    9.

  9. This test isolates the EBTCM class 2 serial data circuit.

    10.

  10. This test isolates the instrument cluster class 2 serial data circuit.

    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

1

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Inoperative

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 5

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 U1255?

Go to Step 4

Go to diagnostic aids

4

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

Go to DTC U1000 Loss of Class 2 Serial Data Fault

Go to Diagnostic Trouble Code (DTC) List

5
  1. Turn off the ignition.
  2. Disconnect the scan tool from the data link connector (DLC).
  3. Inspect for poor connections/terminal tension at the DLC terminals 2 and 5. Refer to Connector Repairs .

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 6

6

Test the DLC ground circuit terminal 5 for an open. Refer to Wiring Repairs .

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 7

7
  1. Disconnect the star connector.
  2. Inspect for poor connections/terminal tension at the star connector. Refer to Connector Repairs .

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 8

8

Test the class 2 serial data circuit for an open or a short between the DLC terminal 2 and the star connector terminal G. Refer to Wiring Repairs .

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 9

9
  1. Using the correct terminal adapter from J35616-A, connect a jumper wire to terminal G of the star connector.
  2. Connect the other end of the jumper wire (with correct terminal adapter) to terminal C 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 11

Go to Step 10

10
  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 Wiring Repairs .

Did you find and correct the condition?

Go to Step 19

Go to Step 17

11
  1. Disconnect the jumper wire from terminal C of the star connector.
  2. Connect the jumper wire to terminal E 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 13

Go to Step 12

12
  1. Turn off the ignition.
  2. Disconnect the SDM.
  3. Test the class 2 serial data 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 Wiring Repairs .

Did you find and correct the condition?

Go to Step 19

Go to Step 17

13
  1. Disconnect the jumper wire from terminal E of the star connector.
  2. Connect the jumper wire to terminal J of the star connector.
  3. Turn on the ignition leaving the engine off.
  4. Attempt to communicate with the EBTCM.

Does the scan tool communicate with the EBTCM?

Go to Step 15

Go to Step 14

14
  1. Turn off the ignition.
  2. Disconnect the EBTCM.
  3. Test the class 2 serial data circuit between the star connector and the EBTCM 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 Wiring Repairs .

Did you find and correct the condition?

Go to Step 19

Go to Step 17

15
  1. Disconnect the jumper wire from terminal J of the star connector.
  2. Connect the jumper wire to terminal L of the star connector.
  3. Turn on the ignition leaving the engine off.
  4. Attempt to communicate with the instrument cluster.

Does the scan tool communicate with the instrument cluster?

Go to Step 19

Go to Step 16

16
  1. Turn off the ignition.
  2. Disconnect the instrument cluster.
  3. Test the class 2 serial data circuit between the star connector and the instrument cluster 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 Wiring Repairs .

Did you find and correct the condition?

Go to Step 19

Go to Step 17

17

Inspect for poor connections/terminal tension at the class 2 serial data circuit of the module that is not communicating. Refer to Connector Repairs .

Did you find and correct the condition?

Go to Step 19

Go to Step 18

18

Replace the module which is not communicating. Refer to the appropriate Repair Instructions for module replacement.

Did you complete the replacement?

Go to Step 19

--

19
  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 21

Go to Step 20

20

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

Go to Step 21

Go to Step 23

21

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

Did you complete the action?

Go to Step 22

--

22

Did you diagnose all of the DTCs?

Go to Step 23

Go to Step 21

23

Clear the DTCs using the scan tool.

Did you complete the action?

System OK

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