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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Chevy C Cab/Chassis HD (GMT 400) 🢒 Engine 🢒 Engine Electrical 🢒 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. 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
    • When the class 2 serial data circuit is shorted to ground, DTC U1300 will be set. Refer to DTC U1300 .
    • When the class 2 serial data circuit is shorted to battery positive voltage, DTC U1301 will be set. Refer to DTC U1301 .

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 circuit. The following modules communicate on the class 2 serial data circuit:

    2. • electronic brake control module (EBCM)
    • powertrain control module (PCM)
    • vehicle theft deterrent (VTD)

  2. The following DTCs may be retrieved with a history status, but are not the cause of the present condition.

    3. • U1300
    • U1301

  3. A State of Health DTC with a history status may be present along with a U1000 or U1255 having a current status. This indicates that the malfunction occurred when the ignition was ON.

    4.

  4. DLC terminal 2 and terminal 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.

    5.

  5. A poor connection at terminal A would cause this condition but will not set a DTC.

    6.

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

    7.

  7. This test isolates the PCM class 2 serial data circuit.

    8.

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

    9.

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

    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

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 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 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 16

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

  1. Turn OFF the ignition.
  2. Remove the scan tool from the 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 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 Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 9

9

Inspect S150 and S280. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 10

10

Test the class 2 circuit for an open or a short. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to the applicable Diagnostic System Check

Go to Step 11

11

  1. Turn OFF the ignition.
  2. Remove the PCM connector that contains the class 2 circuit.
  3. Attempt to communicate with any class 2 module.

Are you able to communicate with any class 2 modules?

Go to Step 15

Go to Step 12

12

  1. Turn OFF the ignition.
  2. Remove the EBCM connector that contains the class 2 circuit.
  3. Attempt to communicate with any class 2 module.

Are you able to communicate with any class 2 modules?

Go to Step 15

Go to Step 13

13

  1. Turn OFF the ignition.
  2. Remove the VTD connector that contains the class 2 circuit.
  3. Connect all other class 2 modules. Previous modules have been eliminated as a possible cause.

Are you able to communicate with any class  2 modules?

Go to Step 15

Go to Step 14

14

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 Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 15

15

Replace the module which is not communicating. Refer to the appropriate repair instructions:

    • EBCM replacement Electronic Brake Control Module Replacement in ABS
    • PCM replacement Powertrain Control Module Replacement in Engine Controls 6.5L
    • PCM replacement Powertrain Control Module Replacement in Engine Controls 8.1L
    • Theft Deterrent Control Module replacement Theft Deterrent Module Replacement in Theft Deterrent

Did you complete the replacement?

Go to Step 16

--

16

  1. Connect all of the modules.
  2. Connect all connectors.
  3. Connect 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 circuit. Remove 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 18

Go to Step 17

17

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

Go to Step 18

Go to Step 19

18

Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Refer to the applicable Diagnostic System Check.

Did you complete the action?

Go to Step 19

--

19

Did you diagnose all of the DTCs?

Go to Step 20

Go to Step 18

20

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

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