GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 Savana - AWD 🢒 Accessories 🢒 Theft Deterrent 🢒 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 BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must be connected to the DLC for any other module to communicate with the scan tool.
    • When the class 2 serial data circuit:
       - is shorted to ground
       - is shorted to voltage

The following DTCs may set:

    • U1300
    • U1301
    • U1305

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 body control module (BCM) sends the appropriate power mode message. If the BCM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate. Early 2004 model vehicles have a redundant class 2 serial data circuit between the BCM and PCM. Late 2004 model vehicles do not have this circuit and it is not necessary to disconnect the PCM to perform this step.

    5.

  5. Normal class 2 serial data communication cannot take place until the body control module (BCM) sends the appropriate power mode message. If the BCM 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 and Inline Harness Connector End Views 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 16

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

--

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. Remove the class 2 serial data splice pack comb.
  2. Disconnect the powertrain control module (PCM) if the vehicle is an early 2004 model.
  3. Using the correct terminal adapter and jumper wire at the spice pack, connect a jumper between the DLC and the body control module (BCM).
  4. Attempt to communicate with the BCM.

Does the scan tool communicate with the BCM?

Go to Step 12

Go to Step 11

11
  1. Test the class 2 serial data circuit(s) to the BCM for the following conditions. Turn ON the ignition when testing for a short to voltage:
    2. • High resistance
    • Open
    • Short to ground
    • Short to voltage
  2. Test the following circuits of the BCM 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 16

Go to Step 14

12

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

Using the correct terminal adapter and jumper wire at the splice pack, perform the following in order to determine which class 2 serial data circuit or module is causing the concern:

  1. Turn ON the ignition, with the engine OFF.
  2. Using the correct terminal adapter and jumper wire, connect each previously disconnected module to the class 2 serial data circuit one at a time until communication with the class 2 serial data circuit is lost.

Did you complete the action?

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 programming or 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 leaving 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

--