GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2003 🢒 CTS - RHD 🢒 Engine 🢒 Engine Controls - 2.6L and 3.2L 🢒 DTC U2104

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) and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure that the required real-time response is maintained.

The CAN serial data line does not communicate with the scan tool via the DLC. CAN serial data information is interpreted by the ECM and transmitted to the serial data line by the ECM.

Conditions for Running the DTC

The CAN circuits are monitored continuously by the modules on the circuit. The only requirement is that the modules are in a RUN power mode.

Conditions for Setting the DTC

The module setting the DTC has attempted to establish communications on the CAN circuits more than 50 seconds.

Action Taken When the DTC Sets

The DTC is set as both current and history, the modules on the CAN network each take separate actions as listed:

    • Engine Control Module (ECM):
       - Turn ON the MIL during the third consecutive drive cycle with the error detected.
       - Record the operating conditions at the time of turning on the MIL and store the data as freeze frame information.
    • Transmission Control Module (TCM):
       - SERVICE TRANSMISSION message is displayed when the first error is detected.
       - Transmission operates in the default mode.

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

Diagnostic Aids

Missing data from a module may assist in diagnosing this malfunction. Determine the module that is not communicating by observing the following:

    • Transmission Data (TCM)
       - Engine Speed (RPM) -- This comes from the ECM.
       - MIL Request -- This goes to the ECM.
    • Engine Data (ECM)
       - Transmission Speed-- This comes from the TCM.
       - MIL Request -- This comes from the TCM.

Test Description

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

  1. A communications failure to one or more modules of a data link circuit may cause the malfunction.

    2.

  2. If a module is not transmitting the required data, the module receiving the data cannot detect the presence of the transmitting module.

    3.

  3. The TCM needs time to reset memory.

Step

Action

Yes

No

Schematic Reference: Data Link Connector Schematics

Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems

1

Did you perform either the Engine Controls, or Transmission, Diagnostic System Check?

Go to Step 2

Go to Control Module References in Body Control System

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, monitor the DTC Information for DTC U2100.
  4. With a scan tool, monitor the DTC Information for DTCs in the range of U2105 - U2106.

Does the scan tool indicate that DTC U2100 or DTCs in the range of U2105 - U2106 as either current or history DTCs?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

Use the scan tool to observe the Data Lists of the ECM, TCM for the data listed:

    • Transmission Data (TCM):
       - Engine Speed (RPM) -- This comes from the ECM.
       - MIL Request -- This goes to the ECM.
    • Engine Data (ECM):
       - Transmission Speed -- This comes from the TCM.
       - MIL Request -- This comes from the TCM.

Either data missing or a mismatch between the data sent and received indicates a malfunction

Does either the lack of information in the data listed or a mismatch between the modules in the data listed indicate an inoperative module?

Go to Step 4

Go to Step 6

4

Inspect for poor connections at the harness connector of the module that is not communicating. 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 9

Go to Step 5

5

Important: Perform the programming or set up procedure for the replaced control module if required.

Replace the control module that is not communicating. Refer to Control Module References in Body Control System.

Did you complete the replacement?

Go to Step 6

--

6

  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition switch.
  3. Wait at least 10 seconds.
  4. Turn the ignition ON, with the engine OFF.
  5. Retrieve DTCs from the ECM and TCM.

Does the DTC reset ?

Go to Step 7

System OK

7

Inspect the connector of the module recording the DTC. 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 9

Go to Step 8

8

Important: Perform the programming or set up procedure for the replaced control module if required.

Replace the control module that has set the DTC. Refer to Control Module References in Body Control System.

Did you complete the replacement?

Go to Step 9

--

9
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition switch.
  3. Wait at least 10 seconds.
  4. Turn the ignition ON, with the engine OFF.
  5. Retrieve DTCs from the ECM and TCM.

Does the DTC reset ?

Go to Step 2

System OK