GM Service Manual Online
For 1990-2009 cars only

Circuit Description

Modules connected to the controller area network (CAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. If no communication is detected on CAN serial data circuit, the DTC is set. A total non communication condition may be caused by a short to battery or voltage on any of the CAN circuits or a short between the CAN high and low circuits.

The following modules communicate on CAN serial data bus:

    • The body control module (BCM)
    • The electronic brake control module (EBCM), if equipped
    • The engine/powertrain control module (ECM/PCM)
    • The transmission control module (TCM), with L61

DTC Descriptor

This diagnostic procedure supports the following DTCs:

    • DTC U2102 More Controllers On Bus Than Programmed
    • DTC U2103 Fewer Controllers On Bus Than Programmed

Conditions for Running the DTC

    • Voltage supplied to the modules is in the normal operating voltage range.
    • The vehicle power mode requires communication to occur.

Conditions for Setting the DTC

Each controller on the CAN serial data circuit monitors the activity or traffic on the bus. The modules have prerecorded information about what messages should be expected during normal functionality. The module setting the DTC does not receive CAN messages from all of the modules it expected to, or receives too many CAN messages. This indicates that there may be fewer controllers or more controllers actively communicating on the bus than programmed.

Action Taken When the DTC Sets

    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) turns ON during the second consecutive drive cycles with the error detected in the ECM.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The ECM records the operating conditions at the time of turning ON the MIL and stores the data as Freeze Frame information.

Conditions for Clearing the MIL/DTC

    • A current DTC and MIL clear when the malfunction is no longer present.
    • A history DTC clears when requested by the scan tool or when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Step

Action

Yes

No

Schematic Reference: Data Communication Schematics

Connector End View Reference: Data Communication Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install the scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. Retrieve DTCs.

Did you record any of the following DTCs, with a current status?

    • U0073
    • U2100
    • U2104
    • Any DTC in range of U0100-U0299, except U0107
    • Any DTC in range of U2105-U2199

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3

Attempt to communicate with all modules that communicate on CAN bus, conform to vehicle options. See circuit description for the list of modules and options.

Does the scan tool communicate with all modules that communicate on CAN bus?

Go to Step 4

Go to Data Link References for the appropriate loss of communication procedure

4

  1. Program the module that had the DTC U2102 or U2103 set. Refer to Control Module References for programming.
  2. Cycle the ignition.
  3. Retrieve DTCs.

Is the DTC U2102 or U2103 still current?

Go to Step 5

Go to Step 6

5

Replace the control module that had set DTC U2102 or U2103. Refer to Control Module References for replacement, setup and programming.

Did you complete the replacement?

Go to Step 6

--

6

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 1

System OK