U0073

DTC U0073

CIRCUIT DESCRIPTION
The engine control module (ECM), electronic brake traction control module (EBTCM) and transmission control module (TCM) if applicable, communicate via a controller area network (CAN) serial data bus. The CAN serial data bus transmits over two wires at speeds high enough to ensure that the required real-time response is maintained. Modules connected to the CAN serial data circuits monitor communications. During normal vehicle operation, information and commands are exchanged among modules. A no communication condition may result from a short to voltage, short to ground, or short between the CAN high and low circuits.

CONDITIONS FOR RUNNING THE DTC
- Voltage supplied to the modules are in the normal voltage range.
- The vehicle power mode requires serial communication to occur.

CONDITIONS FOR SETTING THE DTC
A no communication condition is detected on CAN serial data circuits.

ACTION TAKEN WHEN THE DTC SETS
A module may use a default value for a parameter that it expected to receive via serial data.

CONDITIONS FOR CLEARING THE MIL/DTC
- A current DTC and MIL clear when the malfunction is no longer present.
- A history DTC clears when requested by the scan tool or when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DIAGNOSTIC AIDS
The modules communicating on the CAN serial data circuits are wired parallel to each other. An open in the CAN circuits for one module will not affect other modules. A short to ground or short to voltage on either wire affects all modules no matter where the failure occurs.

TEST DESCRIPTION

Steps 1-7:

Steps 8-12:

The numbers below refer to the step numbers on the diagnostic table.
3. This test isolates a shorted TCM, ECM, or EBTCM. By reading the signal from the ECM after the wiring is tested, without a TCM connected, an ECM signal generating problem can be diagnosed. When the CAN circuits are open between two components, both components generate a 30,000 to 40,000 hertz signal. When the system is not open, the frequency is 3,000 to 3,500 hertz.