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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2006 🢒 TrailBlazer - 2WD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Scan Tool Does Not Communicate with High Speed GMLAN Device

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. When a module detects a bus-off condition, a DTC U2100 will be set. This DTC can be retrieved as history only.

Diagnostic Aids

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 connected at the data link connector (DLC) and the other is at the engine control module (ECM). When testing for a short between high speed GMLAN (+) and (-), a reading of 60 ohms is normal. If the high speed GMLAN serial data is open, testing the resistance between high speed GMLAN (+) and (-) will read about 120 ohms.

The engine will not start when there is a total malfunction of the high speed GMLAN serial data circuits while the engine is not running. 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
    • Any of the high speed GMLAN serial data circuits open

Test Description

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

  1. A partial malfunction in the high speed GMLAN serial data circuits uses a different procedure from a total malfunction of the high speed GMLAN data circuits. The following modules are connected to the high speed GMLAN serial data circuits:

    2. • ECM, for 5.3L
    • Transmission control module (TCM)

  2. Data link connector terminals 6 and 14 provide the connection to the GMLAN serial data high circuit and the GMLAN serial data low circuit respectively.

    3.

  3. The communication malfunction 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

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Important:: Make sure the CANdi module works fine. When functioning properly, CANdi's LED flashes. In the event of a problem, the LED will be constantly illuminated.

  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to communicate with the modules on high speed GMLAN data bus.

Does the scan tool communicate with any module on the GMLAN serial data circuits?

Go to Step 3

Go to Step 5

3

Did you record any DTCs in the range of U2105 to U2199?

Go to DTC U2105-U2199

Go to Step 4

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 the following conditions:
    3. • An intermittent short to ground
    • An intermittent short to voltage
    • An intermittent short between them--Refer to Diagnostic Aids.
    • 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 13

Go to Diagnostic Aids

5

  1. Turn OFF the ignition.
  2. 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 11

Go to Step 6

6
  1. Disconnect the engine control module (ECM).
  2. Turn ON the ignition, with the engine OFF.
  3. Attempt to communicate with the transmission control module (TCM).

Does the scan tool communicate with the TCM?

Go to Step 7

Go to Step 9

7

Inspect for poor connections at the high speed GMLAN serial data circuits of the ECM. 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 11

Go to Step 8

8

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 11

--

9
  1. Turn OFF the ignition.
  2. Disconnect the TCM.
  3. Test the high speed GMLAN circuits between the DLC and the TCM and between the TCM and the ECM for the following conditions:
    4. • An open
    • A short to ground
    • A short to battery
    • A short between them

Refer to the following in Wiring Systems:

    •  Circuit Testing
    •  GMLAN Wiring Repairs

Did you find and correct the condition?

Go to Step 11

Go to Step 10

10

Replace the TCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 11

--

11
  1. Reconnect all of the disconnected modules.
  2. Install a scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. Wait for 10 seconds.

    5. The scan tool may require a power up reset before communication will occur due to a short on the high speed GMLAN serial data circuits. Turn OFF or disconnect the scan tool prior to performing this test.

  5. Select the Display DTCs function for each module.
  6. 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 12

12

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 13

13

Use the scan tool in order to clear the history DTCs.

Did you complete the action?

System OK

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