GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Firebird 🢒 Body and Accessories 🢒 Body Control 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 trouble codes (DTCs) may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure that all of the DTCs are diagnosed and cleared from memory.

Diagnostic Aids

Disconnecting modules and turning the ignition switch to RUN may cause DTCs to set in these modules. Check for DTCs in each module upon completion of the required repair.

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. DTCs U1300 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 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 the star connector 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 EBCM class 2 serial data circuit.

    10.

  10. This test isolates the IPC 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

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 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 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 4

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 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 21

Go to Step 6

6

Is U1000 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. 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 to 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 8

8

Test the DLC ground circuit terminal 5 for an open. Refer to Circuit Testing and to 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 9

9

  1. Disconnect the star connector.
  2. Inspect for poor connections at the star connector. Refer to Testing for Intermittent Conditions and Poor Connections and to 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 10

10

Test the class 2 serial data circuit for an open or a short between the DLC connector and the star connector. Refer to Circuit Testing and to 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 11

11

  1. Connect a 3A fused jumper to the DLC terminal of the star connector.
  2. Connect the other end of the jumper wire to the PCM terminal of the star connector.
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the PCM.

Does the scan tool communicate with the PCM?

Go to Step 13

Go to Step 12

12
  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 with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 19

13

  1. Disconnect the jumper wire from the PCM terminal of the star connector.
  2. Connect the jumper wire to the SDM terminal of the star connector.
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the SDM.

Does the scan tool communicate with the SDM?

Go to Step 15

Go to Step 14

14
  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 with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 19

15

  1. Disconnect the jumper wire from the SDM terminal of the star connector.
  2. Connect the jumper wire to the EBCM terminal of the star connector.
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the EBCM.

Does the scan tool communicate with the EBCM?

Go to Step 17

Go to Step 16

16
  1. Turn OFF the ignition.
  2. Disconnect the EBCM.
  3. Test the class 2 serial data circuit between the star connector and the EBCM for a short to ground or a short to voltage.
  4. Turn ON the ignition with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 19

17

  1. Disconnect the jumper wire from the EBCM terminal of the star connector.
  2. Connect the jumper wire to the IPC terminal of the star connector.
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the IPC.

Does the scan tool communicate with the IPC?

Go to Step 21

Go to Step 18

18
  1. Turn OFF the ignition.
  2. Disconnect the IPC.
  3. Test the class 2 serial data circuit between the star connector and the IPC for a short to ground or a short to voltage.
  4. Turn ON the ignition with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 19

19

Inspect for poor connections at the class 2 serial data circuit of the module that is not communicating. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 20

20

Important: Perform set up procedure if required.

Replace the module which is not communicating. Refer to Control Module References in Body Control System.

Did you complete the replacement?

Go to Step 21

--

21

  1. Reconnect all of the disconnected modules.
  2. Reconnect any other disconnected connectors.
  3. Install a scan tool.
  4. Turn ON the ignition with 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 23

Go to Step 22

22

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

Go to Step 23

Go to Step 25

23

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

Did you complete the action?

Go to Step 24

--

24

Did you diagnose all of the DTCs?

Go to Step 25

Go to Step 23

25

Clear the DTCs using the scan tool.

Did you complete the action?

System OK

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