GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 GMC C Sierra - 2WD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Scan Tool Does Not Communicate with High Speed GMLAN Device

Scan Tool Does Not Communicate with High Speed GMLAN Device HP2

Circuit Description

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications on the high speed GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules.

The scan tool communicates with the following modules via the high speed GMLAN:

    • Energy Storage Control Module (ESCM)
    • Starter/Generator Control Module (SGCM)
    • Electro-Hydraulic Power Steering (EHPS) Module

Diagnostic Aids

Important: The tool communication with the modules connected only to high speed GMLAN data link requires the use of the CANdi module. Due to configuration of this vehicle, they may be communication DTCs set against modules that are able to communicate with the scan tool.

The following conditions may cause a total loss of high speed GMLAN data communication:

    • A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
    • Any of the high speed GMLAN serial data circuits shorted to ground or voltage
    • A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits

Step

Action

Yes

No

Schematic Reference: Data Link Connector Schematics

Connector End View Reference: Master Electrical Component List 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, with the engine OFF.
  2. Retrieve DTCs from the powertrain control module (PCM).

Did you record any DTCs in the range of U1881 to U1899?

Go to DTC U1881-U1899

Go to Step 3

3

Did you record any DTCs in the range of U0100 to U0299?

Go to DTC U0100-U0299

Go to Step 4

4

Attempt to communicate with the following modules:

    • Energy storage control module (ESCM)
    • Starter/Generator control module (SGCM)
    • Electro-hydraulic power steering (EHPS)

Does the scan tool communicate with all listed modules?

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.

  1. Disconnect the scan tool from the data link connector (DLC).
  2. Test the high speed GMLAN serial data circuits for:
    3. • an intermittent short to ground
    • an intermittent short to voltage
    • an intermittent short between high speed GMLAN (+) and (-) circuits
    • an intermittent open on any of the circuits

Refer to the following in Wiring Systems:

    •  Circuit Testing
    •  Connector Repairs
    •  GMLAN Wiring Repairs

Did you find and correct the condition?

Go to Step 10

Go to Diagnostic Aids

6
  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 6 and 14. 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 8

Go to Step 7

7
  1. Disconnect the SGCM.
  2. Repair the high speed GMLAN serial data circuits between DLC connector and SGCM for an open. Refer to GMLAN Wiring Repairs and Connector Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 8

--

8
  1. Reconnect all of the disconnected modules.
  2. Install a scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. Select the Display DTCs function for each module.
  5. 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 Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 9

9

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

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

Go to Step 10

10

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--

Scan Tool Does Not Communicate with High Speed GMLAN Device Diesel

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

High speed GMLAN serial data bus (+)

1

2

1

--

High speed GMLAN serial data bus (-)

1

2

1

--

1. No communication on any high speed GMLAN module.

2. An open in only one high speed GMLAN serial data circuit may allow degraded communication between the modules or no communication with a specific module.

Circuit/System Description

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The high speed GMLAN serial data bus uses two 120 ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is internal to the glow plug control module (GPCM) and the other is internal to the engine control module (ECM)/powertrain control module (PCM). Modules connected to the high speed GMLAN serial data circuits are the GPCM, ECM/PCM, and if equipped, the transmission control module (TCM).

Diagnostic Aids
    • This test is used for a total high speed GMLAN communication failure.
       - If this condition is not current, use of this diagnostic may lead to replacement of a correctly operating component.
       - If only 1 module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
    • Use the Data Link References to identify the high speed GMLAN serial data modules.
    • Use the DMM MIN/MAX function to capture/locate intermittent conditions.
    • The following conditions may cause a total loss of high speed GMLAN data communication:
       - A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
       - Any of the high speed GMLAN serial data circuits shorted to ground or voltage
       - A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits
       - An open in a high speed GMLAN serial data circuit between the DLC and the first splice. This open will cause no communication with the scan tool, and will not affect the module communication on the vehicle.

Reference Information

Schematic Reference

    •  Data Link Connector Schematics
    •  Control Module References

Connector End View Reference

Master Electrical Component List

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Circuit/System Verification

Using a scan tool, attempt to communicate with each module using the High Speed GMLAN serial data circuits. Communication should not be available on any High Speed GMLAN module.

⇒If any module communicates on High Speed GMLAN serial data, refer to DTC U0100-U0299 for diagnostics.

Circuit/System Testing

Important: If this condition is not current, use of this diagnostic may lead to replacement of a correctly operating component.

Automatic Transmission

  1. Ignition OFF, disconnect the harness connector C-2 at the ECM/PCM.
  2. Ignition ON, with a scan tool attempt to communicate with the TCM. Communication should not be available.
    3. ⇒If the TCM communicates, replace the ECM/PCM.
  3. Ignition OFF, disconnect the harness connector at the TCM, and reconnect the connector to the ECM/PCM.
  4. Ignition ON, with a scan tool attempt to communicate with the ECM/PCM. Communication should be available.
    5. ⇒If the ECM/PCM does not communicate, test the serial data circuits between the TCM and ECM/PCM and DLC for a short ground, voltage, or a short between the circuits.
  5. Ignition OFF, disconnect connector C-2 of the GPCM, and reconnect the connectors of the TCM.
  6. Ignition ON, with a scan tool attempt to communicate with the ECM/PCM. Communication should be available.
    7. ⇒If the ECM/PCM does not communicate, test the serial data circuits between the TCM and GPCM for a short ground, voltage, or a short between the circuits. If the circuits test normal, test or replace the TCM.
  7. Test or replace the GPCM.

Manual Transmission

  1. Ignition OFF, disconnect the harness connector C-2 at the GPCM.
  2. Ignition ON, with a scan tool attempt to communicate with the ECM/PCM. Communication should not be available.
    3. ⇒If the ECM/PCM communicates, replace the GPCM.
  3. Ignition OFF, disconnect the harness connector C-2 at the ECM/PCM.
  4. Test for less than 5 ohms of resistance between the serial data terminal 6 of the DLC and the serial data terminal 57 of the ECM/PCM, and between the serial data terminal 14 of the DLC and the serial data terminal 44 of the ECM/PCM.
    5. ⇒If greater than 5 ohms, repair the data circuit for open/high resistance between the DLC and the first splice.
  5. Both modules still disconnected, test for infinite resistance between the serial data terminal 6 and terminal 14 of the DLC.
    6. ⇒If less than infinite resistance, repair the short between the serial data circuits.
  6. Ignition on, both modules still disconnected, test for less than 1 volt between the serial data terminals 6, and 14 of the DLC and ground.
    7. ⇒If greater than 1 volt, repair the serial data circuit for a short to voltage.
  7. Both modules disconnected, test for infinite resistance between the high speed GMLAN serial data circuits of the DLC and ground.
    8. ⇒If less than infinite resistance, repair the serial data circuits for a short to ground.
  8. If all circuits test normal, test or replace the ECM/PCM.

Component Test

TCM-Communication

  1. Ignition OFF, disconnect the harness connector at the TCM, and connector C-2 at the ECM/PCM and GPCM. Install the J-39700 breakout box, the J-47275 breakout box adapter and the J-47275-1 magnetic overlay. Jumper the serial data pin 6 to pin 26 at the J-39700 breakout box in order to utilize the 120 ohm resistor internal to the TCM.
  2. Ignition ON, with a scan tool attempt to communicate with the TCM. Communication should be available.
    3. ⇒If the TCM does not communicate, replace the TCM.
  3. If the TCM does communicate, the condition may be intermittent and/or another module/circuit. Refer to Diagnostic Aids.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

    •  Control Module References for module replacement, setup, and programming
    •  GMLAN Wiring Repairs

Scan Tool Does Not Communicate with High Speed GMLAN Device 8.1L

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Circuit/System Description

The scan tool uses the High Speed GMLAN Serial Data (+) and (-) circuits to communicate with the transmission control module (TCM).

Reference Information

Schematic Reference

    •  Data Link Connector Schematics
    •  Control Module References

Connector End View Reference

Master Electrical Component List

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Circuit/System Verification

Using a scan tool, attempt to communicate with the TCM. The scan tool should communicate with the High Speed GMLAN device.

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the TCM.
  2. Ignition ON, verify that a test lamp does not illuminate between the following circuits and ground:
    3. • High Speed GMLAN Serial Data (+) terminal 6
    • High Speed GMLAN Serial Data (+) terminal 26
    • High Speed GMLAN Serial Data (-) terminal 27
    ⇒If the test lamp illuminates, test the affected circuit for a short to B+.
  3. Verify that a test lamp does not illuminate between the following circuits and B+:
    4. • High Speed GMLAN Serial Data (+) terminal 6
    • High Speed GMLAN Serial Data (+) terminal 26
    • High Speed GMLAN Serial Data (-) terminal 27
    ⇒If the test lamp illuminates, test the affected circuit for a short to ground.
  4. Test for less than 1.0 ohm of resistance between the following terminals:
    5. • High Speed GMLAN Serial Data (+) terminal 6 at the TCM and terminal 6 at the DLC
    • High Speed GMLAN Serial Data (+) terminal 26 and terminal 6 at the DLC
    • High Speed GMLAN Serial Data (-) terminal 27 and terminal 14 at the DLC
    ⇒If greater than the specified range, test the affected circuit for an open/high resistance.
  5. Test for infinite resistance between the following terminals:
    6. • High Speed GMLAN Serial Data (+) terminal 6 at the TCM and terminal 14 at the DLC
    • High Speed GMLAN Serial Data (+) terminal 26 and terminal 14 at the DLC
    • High Speed GMLAN Serial Data (-) terminal 27 and terminal 6 at the DLC
    ⇒If less than the specified value, test the affected circuits for a short to each other.
  6. If all circuits test normal, replace the TCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for TCM replacement, setup, and programming