GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Express - AWD 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Scan Tool Does Not Communicate with High Speed GMLAN Device

Circuit Description

The GMLAN serial data circuits are high speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. The GMLAN serial data circuits also connect directly to the data link connector (DLC).

Modules connected to the GMLAN serial data circuits monitor communications during normal vehicle operation, where operation information is exchanged among the modules.

A CANdi Module is necessary between the scan tool and the ALDL and acts as a transceiver for the scan tool communications with the GMLAN modules. If a CANdi module is not used there may be no communication messages for the specific GMLAN modules.

The scan tool communicates with the following modules on the high speed GMLAN serial data circuits:

    • Auxiliary Heater Control Module (FOH) (w/K08, Coolant Heater)
    • Engine control module (ECM)
    • Glow plug control module (GPCM)
    • Transmission control module (TCM)

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, not using a CANdi module may cause scan tool communication errors against modules that should 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 Communication Schematics

Connector End View Reference: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

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

Go to DTC U0100-U0299

Go to Step 3

3

Using the list in the circuit description, attempt to communicate with the following modules:

    • Auxiliary Heater Control Module (FOH) (w/K08, Coolant Heater)
    • Engine control module (ECM)
    • Glow plug control module (GPCM)
    • Transmission control module (TCM)

Does the scan tool communicate with all equipped modules?

Go to Step 4

Go to Step 5

4

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

Refer to the following:

    •  Circuit Testing
    •  Connector Repairs
    •  GMLAN Wiring Repairs

Did you find and correct the condition?

Go to Step 9

Go to Diagnostic Aids

5
  1. Turn OFF the ignition.
  2. Disconnect the scan tool from the 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 .

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6
  1. Disconnect the ECM.
  2. Repair the high speed GMLAN serial data circuits between DLC connector and ECM for an open. Refer to GMLAN Wiring Repairs and Connector Repairs .

Did you complete the repair?

Go to Step 7

--

7
  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

Go to Step 8

8

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

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 9

9

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--