Here are the diagnostics with diagram.
The Controller Area Network (CAN) serial data circuit is a high speed serial data bus used to communicate information between the Electronic Brake and Traction Control Module (EBTCM), the Engine Control Module (ECM) and the Transmission Control Module (TCM). When the ignition switch is turned to the ON position, the modules begin to transmit data between each other. The following data is transmitted and received between the ECM and TCM:
The following data is transmitted and received between the ECM and EBTCM:
The addressing scheme employed with CAN assigns a label to every message, with each message receiving a unique "identifier". The identifier classifies the content of the message (such as engine speed). Each module processes only those messages whose identifiers are stored in the module's acceptance list. This is CAN's form of message filtering.
The identifier labels both the data content and the priority of the message being sent. Each module can begin transmitting its most important data as soon as the bus is unoccupied. When more than one module starts to transmit simultaneously, the message with the highest priority is assigned first access. A module responds to failure to gain access by automatically switching to receive mode, the module then repeats the transmission attempt as soon as the bus is free again.
Conditions for Running the DTC
The CAN Bus circuit is monitored continuously after the ignition switch is turned to the ON position.
Conditions for Setting the DTC
The ECM and TCM monitor the received messages from the EBTCM for corruption or for missing messages. 3 seconds after initialization, the control module that has set the DTC is not receiving a message back from the EBTCM, or the message is corrupted.
Action Taken When the DTC Sets
The following describes the action taken when the code is set in a particular control module.
The following describes the conditions for clearing the MIL/DTC in a particular control module.
This DTC is confined to a malfunction with the control module that the DTC was set in, or the control module(s) that is connected to the module the code was set in. A physical malfunction of the harness is not the cause of this DTC. If there is a malfunction with the CAN Bus harness, DTC U2100 will be set.
The scan tool can be used as an aid in diagnosing this DTC. In the scan tool data display, observe the following parameters that are transmitted over the CAN Bus:
Observing the data display parameters for abnormalities or missing data may pinpoint which control module is causing the malfunction.
The number(s) below refer to the step number(s) on the diagnostic table.
A DTC U2100 set in either the ECM, TCM or EBTCM may have caused U2108 to set. You must diagnose and clear DTC U2100 to determine if it is the cause of U2108 setting.
If the Electronic Brake Traction Control Module (EBTCM) loses power, it will cause other module(s) to set Lost Communication DTCs.
The malfunction is due to an open in the CAN Bus serial data circuit or an open in the module.
Because of the malfunction, the EBTCM may have set CAN Bus DTCs for those modules that it was monitoring.
The Engine Control Module (ECM) and Transmission Control Module (TCM) may have set other CAN Bus DTCs because of the original malfunction. You must clear the DTCs from these modules to avoid future misdiagnosis.
Did you perform the applicable diagnostic system check for one of the following modules?
Go to Step 2
Go to the Applicable Diagnostic System Check
Was DTC U2100 recorded as a history or current DTC in the ECM, TCM or EBTCM?
Go to diagnostic table DTC U2100 CAN-BUS Communication Malfunction
Go to Step 3
Did you find and correct the condition?
Go to Step 8
Go to Step 4
Inspect for poor connections/terminal tension at the CAN Bus serial data circuit(s) of the module that set DTC U2108. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Go to Step 5
Test the CAN Bus serial data circuit(s) for an open between the module that set DTC U2108 and the EBTCM. Refer to Testing for Continuity in Wiring Systems.
Go to Step 6
Inspect for poor connections/terminal tension at the CAN Bus serial data circuit(s) of the EBTCM. If DTC U2108 was set in the TCM, also inspect for poor connections/terminal tension at the CAN Bus serial data circuit(s) of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Go to Step 7
Replace the EBTCM. Refer to Electronic Brake and Traction Control Module Replacement in Antilock Brake System.
Did you complete the replacement?
Go to Step 10
Does the scan tool display any DTCs other than the following?
Go to Diagnostic System Check - ABS in Antilock Brake System
Go to Step 9
Use the scan tool in order to clear the DTCs.
Did you complete the action?
Select the Display DTCs function for the module(s) which set DTC U2108.
Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls 3.0L and/or Diagnostic System Check - ABS in Automatic Transmission 4L30-E
Go to Step 11