GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Catera 🢒 Body and Accessories 🢒 Data Link Communications 🢒 DTC U2100

Circuit Description

The controller area network (CAN) is a high speed system for sharing data. The circuit consists of a two wire twisted pair connecting the ECM to the TCM and a second twisted pair connecting the ECM to the EBCM.

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 ON power mode.

Conditions for Setting the DTC

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

Action Taken When the DTC Sets

Besides storing the DTC 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 second 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):
       - Turn ON the Service Transmission Lamp (STL) when the first error is detected.
       - Send a request to the ECM to turn ON the MIL during the second consecutive drive cycle with the error detected.
       - Operate in the Default Mode. Refer to Electronic Component Description in Automatic Transmission-4L30-E.
    • Electronic Brake Control Module (EBCM):
       - Traction Control System (TCS) is disabled.
       - Turn ON the TC indicator.

Conditions for Clearing the MIL/DTC

The MIL, STL and TC indicators are cleared, turned OFF, and the DTC cleared by a different strategy for each module:

    • ECM:
       - If the fault is not detected for three consecutive drive cycles the current DTC is cleared and the MIL is turned OFF.
       - The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles.
       - The history DTC is cleared if there is a KAM reset (battery disconnected).
    • TCM:
       - If the fault is not detected for one drive cycle the current DTC is cleared and the STL is turned OFF.
       - The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles.
       - The Default Mode transmission control is cancelled when the malfunction is not present and the ignition switch is OFF long enough for the TCM to power-down and reset.
    • EBCM:
       - If the fault is not detected for one drive cycle the current DTC is cleared and the TC indicator is turned OFF.
       - The history DTC is cleared if the malfunction does not reoccur for 100 consecutive drive cycles.

Step

Action

Yes

No

Schematic Reference: Data Link Connector Schematics

1

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

Go to Step 2

Go to Control Module References in Body Control System

2
  1. Turn OFF the ignition.
  2. Disconnect the connectors on the EBCM, ECM and TCM.
  3. Test the CAN high and low circuits for all three modules or shorts to ground, B+ and each other. Turn ON the ignition, with the engine OFF when you test for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Reconnect all components.
  3. Connect a scan tool to the vehicle.
  4. Use the scan tool in order to clear the DTC.
  5. Turn OFF the ignition.
  6. Disconnect the EBCM and the TCM connectors.
  7. Turn the ignition ON, with the engine OFF.
  8. Use the scan tool to view DTCs in the ECM.

Does the DTC U2100 reset?

Go to Step 6

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Reconnect the TCM connector.
  3. Turn the ignition ON, with the engine OFF.
  4. Use the scan tool to view DTCs in the ECM and the TCM.

Does the DTC U2100 reset?

Go to Step 6

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Reconnect the EBCM connector.
  3. Turn the ignition ON, with the engine OFF.
  4. Use the scan tool to view DTCs in the ECM, TCM and the EBCM.

Does the DTC U2100 reset?

Go to Step 6

System OK

6

Inspect for poor connections at the harness connector of the module that was last connected. 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 8

Go to Step 7

7

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

Replace the control module that was last connected. Refer to Control Module References in Body Control System.

Did you complete the replacement?

Go to Step 8

--

8
  1. Reconnect all modules not already connected.
  2. Use the scan tool in order to clear the DTCs.
  3. Turn OFF the ignition switch.
  4. Wait at least 10 seconds.
  5. Turn the ignition ON, with the engine OFF.
  6. Retrieve DTCs from the ECM, EBCM and TCM.

Does the DTC reset ?

Go to Step 2

System OK