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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Blazer - 2WD 🢒 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. • The body control module (BCM)
    • The driver information center (DIC), w/Trip
    • The electronic brake control module (EBCM)
    • The inflatable restraint sensing and diagnostic module (SDM)
    • The instrument panel cluster (IPC)
    • The memory seat module (MSM) - driver, w/D44
    • The powertrain control module (PCM)
    • The radio
    • The transfer case shift control module (TCSCM), w/NP8

  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 or U1255 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 SP201 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 splice pack SP201 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 wire for a short, make sure there is not a module connected to the wire being tested. This test isolates the BCM class 2 serial data circuits.

    8.

  8. There is a redundant class 2 serial data circuit between BCM and PCM.

    9.

  9. 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 rest of the splice pack SP201 serial data circuits.

    10.

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

    11.

  11. 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 and Inline Harness Connector End Views 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 in Wiring Systems:

    •  Circuit Testing
    •  Connector Repairs
    •  Wiring Repairs

Did you find and correct the condition?

Go to Step 20

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

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 Vehicle DTC 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 Vehicle DTC 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 Vehicle DTC Information

Go to Step 10

10

  1. Disconnect the splice pack SP201.
  2. Inspect for poor connections at the splice pack 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 Diagnostic System Check - Vehicle in Vehicle DTC Information

Go to Step 11

11

Test the class 2 serial data circuit between the DLC and the splice pack SP201 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 Diagnostic System Check - Vehicle in Vehicle DTC Information

Go to Step 12

12

  1. Using the correct terminal adapter, connect a jumper wire to the DLC terminal of the splice pack SP201.
  2. Connect the other end of the jumper wire, using correct terminal adapter, to the body control module (BCM) terminal of the splice pack SP201.
  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 circuits between PCM and DLC 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 20

Go to Step 18

15
  1. Turn OFF the ignition.
  2. Disconnect the BCM.
  3. Test the 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 20

Go to Step 18

16

Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP201 until the concern is located:

  1. Leave the jumper wire connected to the DLC terminal and to the BCM terminal of the splice pack SP201.
  2. Connect the jumper wire, using correct terminal adapter, to the terminal for the rest of devices connected to splice pack SP201.
  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 20

Go to Step 17

17
  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 SP201 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 20

Go to Step 18

18

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 20

Go to Step 19

19

Replace the last disconnected module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 20

--

20

  1. Reconnect all of the disconnected modules.
  2. Install a scan tool.
  3. Turn ON the ignition leaving the engine OFF.
  4. Wait for 10 seconds.

    5. 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.

  5. 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.
  6. 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 21

21

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

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

Go to Step 22

22

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

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