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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 Safari - 2WD 🢒 Preface 🢒 Cautions and Notices 🢒 Scan Tool Does Not Communicate with Class 2 Device

Circuit Description

Each module connected to the class 2 serial data circuit monitors serial data communication 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
    • The body control module (BCM) detects that the ignition is ON and sends the appropriate power mode message to the other class 2 modules. Therefore, the BCM must be connected to the class 2 serial data circuit for any other module to communicate with the scan tool.
    • When the class 2 serial data circuit is shorted to voltage or ground, DTCs U1300, U1301, or U1305 may set.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. A partial loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication 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 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.

    4.

  4. Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.

    5.

  5. Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.

    6.

  6. If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.

    7.

  7. The communication concern 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 in Wiring Systems.

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.

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 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 18

Go to Step 6

6

Are U1000 or U1255 the only DTCs 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 Lost Communications with XXX procedure for the module which is not communicating. The DTC U1001--U1254 Lost Communications with XXX procedure will determine which module is not communicating. Refer to DTC U1001-U1254 .

Did you complete the action?

Go to Control Module References in Body Control System for the applicable Diagnostic System Check

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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 and terminal tension 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 in Body Control System for the applicable Diagnostic System Check

Go to Step 9

9

Test the signal ground circuits of the DLC for an open or high resistance. 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 in Body Control System for the applicable Diagnostic System Check

Go to Step 10

10

  1. Disconnect the powertrain control module (PCM).
  2. Disconnect the splice pack by removing the comb.
  3. Use a jumper to connect the power mode master (PMM), terminal M, to the data link connector, terminal A, of the class 2 serial data circuit. To identify which module is the PMM, refer to Body Control System Description and Operation in Body Control System.
  4. Attempt to communicate with the PMM.

Does the scan tool communicate with the PMM?

Go to Step 12

Go to Step 11

11
  1. Test the class 2 serial data circuit between the DLC and the PMM for the following conditions. Turn ON the ignition when testing for a short to voltage:
    2. • High resistance
    • An open
    • Short to ground
    • Short to voltage
  2. Test the following circuits of the PMM for an open or high resistance:
    3. • The battery positive voltage input circuits
    • The battery positive voltage output circuits
    • The ignition voltage input circuits
    • The ignition voltage output circuits
    • The switched battery positive voltage supply circuits
    • The ground circuits

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 16

12

Important: The PMM must remain connected to the DLC. Use the appropriate jumper if needed.

Starting with the modules furthest from the DLC. Perform the following for each module, in order to determine the location of the concern:

  1. Turn OFF the ignition.
  2. One at a time, use a jumper to connect each of the modules to the class 2 serial data circuit at the splice pack.
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with the PMM.
  5. Continue step 1 through step 4 until all modules are connected or connecting a module stops communication.

Did the scan tool continue to communicate with the PMM as modules were connected to the class 2 serial data circuit?

Go to Step 16

Go to Step 13

13

  1. Test the class 2 serial data circuits to the suspect module for a short to ground or a short to voltage.
  2. Turn ON the ignition, with 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 16

Go to Step 14

14

Inspect for poor connections and terminal tension at the harness connector of the suspect module. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 15

15

Important:  Perform the module setup procedure if required.

Replace the suspect module. Refer to Control Module References in Body Control System for the appropriate Repair Instructions for module replacement.

Did you complete the replacement?

Go to Step 16

--

16

  1. Connect all of the modules.
  2. Connect all the connectors.
  3. Install a scan tool.
  4. Turn ON the ignition, with 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 letter "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 letter "U"?

Go to Step 18

Go to Step 19

18

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

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

Clear the DTCs using the scan tool.

Did you complete the action?

Go to Control Module References in Body Control System for the applicable Diagnostic System Check

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