LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Buick >> 2005 >> Century Base >> Repair and Diagnosis >> External Pages >> Different car >> Section 2 (Data Link Communication System) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with Class 2 Device >> Test Description
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Test Description

WARNING: This page is about a different car, the 2004 Buick Regal and 2004 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 2:  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:
    • PCM
    • EBCM
    • SDM
    • IPC
    • BCM
    • HVAC Control Module
    • VCIM.
  2. 3:  The following DTCs may be retrieved with a history status, but are not the cause of the present condition.
    • U1300
    • U1301
  3. 6:  A State of Health DTC for a specific module 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. 7:  Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
  5. 9:  A poor connection at the star connector terminal for the DLC would cause this condition but will not set a DTC.
  6. 10:  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. 11:  The BCM detects the ignition switch position and sends the appropriate power mode message to the other modules. The BCM must remain connected to the DLC for any other module to communicate with the scan tool. This test isolates the BCM class 2 serial data circuit.
  8. 13:  This test isolates the PCM class 2 serial data circuit.
  9. 15:  This test isolates the EBCM class 2 serial data circuit.
  10. 17:  This test isolates the SDM class 2 serial data circuit.
  11. 19:  This test isolates the IPC class 2 serial data circuit.
  12. 21:  This test isolates the HVAC Control Module class 2 serial data circuit.
  13. 23:  This test isolates the VCIM class 2 serial data circuit.
  14. 26:  The communication malfunction may have prevented diagnosis of the customer complaint.
  15. 27:  If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
Scan Tool Does Not Communicate with Class 2 Device

Step Action Yes No
Schematic Reference: Data Link Connector (DLC) Schematics 
Connector End View Reference: Master Electrical Component List
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. 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 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 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following in Wiring Systems:Did you find and correct the condition?		 Go to Step 27  Go to Step 6 
6  Is U1000 or U1255 the only DTCs 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 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 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 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 and the star connector. Refer to Circuit Testing and 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 jumper wire to the DLC terminal of the star connector. Connect the other end of the jumper wire to the BCM terminal of the star connector.
  2. Turn ON the ignition, with the engine OFF.
  3. Attempt to communicate with the BCM.
Does the scan tool communicate with the BCM?		 Go to Step 13  Go to Step 12 
12
  1. Turn OFF the ignition.
  2. Disconnect the BCM.
  3. Test the class 2 serial data circuit between the star connector and the BCM for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Turn ON the ignition, with the engine OFF, when testing for a short to voltage.
Did you find and correct the condition?		 Go to Step 27  Go to Step 25 
13 
  1. Leave the jumper wire connected to the DLC terminal and to the BCM terminal of the star connector. Connect another jumper wire to the jumper wire connected 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 15  Go to Step 14 
14
  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. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Turn ON the ignition, leaving the engine OFF, when testing for a short to voltage.
Did you find and correct the condition?		 Go to Step 27  Go to Step 25 
15 
  1. Disconnect the jumper wire from the PCM 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. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Turn ON the ignition, leaving the engine OFF, when testing for a short to voltage.
Did you find and correct the condition?		 Go to Step 27  Go to Step 25 
17 
  1. Disconnect the jumper wire from the EBCM 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 19  Go to Step 18 
18
  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. Refer to Circuit Testing and Wiring Repairs in Wiring System. Turn ON the ignition, with the engine OFF, when testing for a short to voltage.
Did you find and correct the condition?		 Go to Step 27  Go to Step 25 
19 
  1. Disconnect the jumper wire from the SDM 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 20 
20
  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. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Turn ON the ignition, with the engine OFF, when testing for a short to voltage.
Did you find and correct the condition?		 Go to Step 27  Go to Step 25 
21 
  1. Disconnect the jumper wire from the IPC terminal of the star connector.
  2. Connect the jumper wire to the HVAC Control Module terminal of the star connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with the HVAC Control Module.
Does the scan tool communicate with the HVAC Control Module?		 Go to Step 23  Go to Step 22 
22
  1. Turn OFF the ignition.
  2. Disconnect the HVAC Control Module.
  3. Test the class 2 serial data circuit between the star connector and the HVAC Control Module for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Turn ON the ignition, with the engine OFF, when testing for a short to voltage.
Did you find and correct the condition?		 Go to Step 27  Go to Step 25 
23 
  1. Disconnect the jumper wire from the HVAC Control Module terminal of the star connector.
  2. Connect the jumper wire to the VCIM terminal of the star connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with the VCIM.
Does the scan tool communicate with the VCIM?		 Go to Step 27  Go to Step 24 
24
  1. Turn OFF the ignition.
  2. Disconnect the VCIM.
  3. Test the class 2 serial data circuit between the star connector and the VCIM for a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Turn ON the ignition, with the engine OFF, when testing for a short to voltage.
Did you find and correct the condition?		 Go to Step 27  Go to Step 25 
25 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 27  Go to Step 26 
26 
IMPORTANT: Perform the setup procedure for the module if required.
Replace the module that is not communicating. Refer to Control Module References in Body Control System for the appropriate repair instructions.Did you complete the repair?		 Go to Step 27  -
27 
  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 if there was 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 current DTCs that begin with a "U"?		 Go to Step 29  Go to Step 28 
28 Did you record any DTCs that do not begin with a "U"? Go to Step 29  Go to Step 31 
29 Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Refer to Control Module References in Body Control System for the applicable Diagnostic System Check.
Did you complete the action?		 Go to Step 30  -
30 Did you diagnose all of the DTCs? Go to Step 31  Go to Step 29 
31 Use the scan tool in order to clear the DTCs.
Did you complete the action?		 System OK -
scientia non olet · About LEMON Manuals