U2104

DTC U2104

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 (LB7 engine):
- The engine control module (ECM)
- The transmission control module (TCM), w/M74
- The fuel injector control module (FICM)

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC U2104 Controller Area Network (CAN) Bus Reset Counter Overrun

CONDITIONS FOR RUNNING THE DTCS
- Voltage supplied to the modules is in the normal operating voltage range.
- The engine is running.

CONDITIONS FOR SETTING THE DTC
A total non-communication condition is detected on CAN serial data circuit.

ACTION TAKEN WHEN THE DTC SETS
- The module uses a default value for the missing parameter.
- The malfunction indicator lamp (MIL) will illuminate on the second consecutive ignition cycle that the diagnostic runs and fails, for the type B DTCs. For a detailed description about DTCs types refer to Diagnostic Trouble Code (DTC) Type Definitions in Computers and Control Systems - 6.6L (LB7). Diagnostic Trouble Code Descriptions

CONDITIONS FOR CLEARING THE MIL/DTC
The MIL/DTC clearing depends on DTC type. For information about DTC type refer to Diagnostic Trouble Code (DTC) Type(s) in Computers and Control Systems - 6.6L (LB7). Diagnostic Trouble Code Descriptions

DTC TYPE B
- The MIL clears after 3 ignition cycles when the malfunction is no longer present.
- 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.

DTC TYPE C
- 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.

TEST DESCRIPTION

Step 1:

Step 2:

Steps 3 - 6:

Steps 7 - 10:

Steps 11 - 12:

The number below refers to the step number on the diagnostic table.
3. This test isolates a shorted FICM from a shorted TCM or ECM. By reading the signal from the FICM after the wiring has been tested, without a TCM connected, an FICM signal generating problem can be diagnosed. When the CAN circuits are open between 2 components, both components generate a 30,000-40,000 Hertz signal. When the system is not open, the frequency is 3,000-3,500 Hertz.