GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2006 🢒 Equinox 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 DTC U2105-U2199

Circuit 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. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC U2105 Lost Communication With Engine Control Module (ECM)
    • DTC U2106 Lost Communication With Transmission Control Module (TCM)
    • DTC U2107 Lost Communication With Body Control Module (BCM)
    • DTC U2108 Lost Communication With Electronic Brake Control Module (EBCM)

Conditions for Running the DTCs
    • Voltage supplied to the modules is in the normal operating voltage range.
    • The vehicle power mode requires serial data communication to occur.
    • The DTC U2100 does not have a current status.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

The module uses a default value for the missing parameter.

Conditions for Clearing the DTC
    • A current DTC clears when the malfunction is no longer present.
    • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids
    • A poor connection at the inoperative module may cause this code to set.
    • An improperly powered module may cause this code to set.

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. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Attempt to communicate with BCM.

Were you able to communicate with BCM?

Go to Step 3

Go to Scan Tool Does Not Communicate with Class 2 Device

3

Attempt to communicate with EBCM, if equipped or with TCM, if not equipped with EBCM.

Were you able to communicate with EBCM/TCM?

Go to Step 8

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the vehicle communication interface module (VCIM).
  3. Bypass the VCIM installing jumpers between GMLAN serial data circuits at the VCIM connector:
    4. • Connect a jumper between high speed GMLAN bus (+) circuit to BCM and high speed GMLAN bus (+) circuit to the EBCM/TCM.
    • Connect a jumper between high speed GMLAN bus (-) circuit to BCM and high speed GMLAN bus (-) circuit to the EBCM/TCM.
  4. Attempt to communicate with EBCM, if equipped, or with TCM, if not equipped with EBCM.

Were you able to communicate with EBCM/TCM?

Go to Step 5

Go to Step 7

5

Test the high speed GMLAN serial data circuits of the VCIM for poor connections. 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 13

Go to Step 6

6

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

Did you complete the replacement?

Go to Step 13

--

7
  1. Turn OFF the ignition.
  2. Test the high speed GMLAN serial data circuits between BCM and EBCM/TCM for an open. Refer to the following:
    3. •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  GMLAN Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 13

Go to Step 8

8

Important:: Use the DTC Descriptor list to determine the closest module to DLC which is not communicating.

Test the following circuits of the closest module to DLC that is not communicating, for an open or a short to ground:

    • The battery positive circuits
    • The battery voltage output circuits
    • The switched battery positive voltage circuits

Refer to the following:

    •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 13

Go to Step 9

9
  1. Turn OFF the ignition.
  2. Test the ground circuits of the closest module to DLC that is not communicating, for an open. Refer to the following:
    3. •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 13

Go to Step 10

10

Test the high speed GMLAN serial data circuits of the closest module to DLC that is not communicating, for an open. Refer to the following:

    •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  GMLAN Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 13

Go to Step 11

11

Test the following circuits of the closest module to DLC that is not communicating, for poor connections:

    • The battery positive voltage circuits
    • The battery voltage output circuits
    • The switched battery positive voltage circuits
    • The ground circuits
    • The high speed GMLAN serial data circuits

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 13

Go to Step 12

12

Replace the closest module to DLC that is not communicating. Refer to Control Module References for replacement, setup and programming.

Did you complete the replacement?

Go to Step 13

--

13
  1. Reconnect all disconnected modules.
  2. Turn ON the ignition, with the engine OFF.
  3. Use the scan tool in order to clear the DTCs.

Does the scan tool still display any other current DTCs?

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

System OK