GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2007 🢒 ION 🢒 DTC 🢒 DTC U2100

Circuit Description

The controller area network (CAN) serial data line is a high speed serial data bus used to communicate information between the engine control module (ECM), body control module (BCM), and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure the required real-time response is maintained. The CAN serial data line does not communicate with the scan tool via the data link connector (DLC). CAN serial data information is interpreted by the BCM and transmitted to the serial data line by the BCM.

Modules connected to the CAN serial data circuit monitors communication during normal vehicle operation, where operation information is exchanged among the modules. Each module on the CAN network maintains a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255, the controller removes itself from the network and DTC U2100 will result.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC U2100 Controller Area Network (CAN) Bus Communication

Conditions for Running the DTCs
    • Supply voltage to the modules are in the normal operating range.
    • The vehicle is in the RUN power mode.

Conditions for Setting the DTC

The module setting the DTC has attempted to establish communications on the CAN circuits for more than 7 times.

Action Taken When the DTCs Sets
    • The module suspends all message transmission.
    • The module uses default values for all parameters received on the serial data circuits.
    • The module inhibits the setting of all other communication DTCs.

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
    • This DTC cannot be retrieved with a current status. Diagnosis of current DTC is accomplished via the symptom, Scan Tool Does Not Communicate with High Speed GMLAN Device.
    • An intermittent condition is likely to be caused by a short on the GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with High Speed GMLAN Device procedure in order to isolate an intermittent condition.

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
  1. Turn the ignition OFF.
  2. Disconnect the body control module (BCM), engine control module (ECM), electronic brake control module (EBCM), and transmission control module (TCM) connectors.
  3. Test both the controller area network (CAN) high and low circuits for the following conditions:
    4. • A short to ground
    • A short to voltage
    • A short to each other

Turn the ignition ON, with the engine OFF when you test for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 5

Go to Step 3

3
  1. Using the scan tool, clear the DTCs.
  2. Turn the ignition OFF.
  3. Reconnect each module one at a time, starting with the TCM, then the BCM, the EBCM, and finally the ECM.
  4. After each module is connected, check for U2100 in the ECM and EBCM.

Does DTC U2100 reset after reconnecting each module one at a time?

Go to Step 5

Go to Step 4

4

Replace the module that resets U2100. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 5

--

5
  1. Reconnect all modules not already connected.
  2. Use the scan tool in order to clear the DTCs.
  3. Turn the ignition switch OFF.
  4. Wait at least 10 seconds.
  5. Turn the ignition ON, with the engine OFF.
  6. Retrieve DTCs from the ECM and EBCM.

Does the DTC reset ?

Go to Step 2

System OK