U0003 - High Speed Can Communication Bus (+) Open

The Controller Area Network (CAN) is a complex automotive bus network that interconnects various devices without a central computer. Between the devices, there’s an exchange of data and working parameters, which are loaded with information about the messages to be exchanged via the serial data circuits.

There are two specific wires to carry out the communication for the CAN bus (CAN high and CAN low). At idle, the CAN bus lines have 2.5 volts. In bit communication, the high CAN carries 3.75, while the low one carries 1.25 volts. This way, they maintain a differential of 2.5 between both lines.

To send information via both CAN buses, it is executed through the Totally Integrated Power Module (TIMP). Utilizing codes, the TIMP identifies which module is sending information. This transmission of information is called binary conversation.

The diagnostic code U0003 OBDII is stored when a problem is detected on the high-speed CAN communication bus due to an open circuit. OBDII Fault Codes correspond to the U-Codes (Network Communications) also known as network communications codes. This fault code applies to all communication components of the vehicle’s electronic system.

Automobiles that have an Electronic Control Module (ECM), which serves as the brain of the vehicle, are responsible for sending and receiving information from all the electronic modules of the automobile. So a U-Codes type failure symbolizes a deficiency somewhere in the ECM.

• Check Engine light illuminates.
• Unexpected engine shutdown.
• Engine starting is difficult.
• Irregular engine operation.
• Unexpected activation of the vehicle alarm.

OBD2 fault code U0003 is set by the following:

• If an OBD2 U0003 fault is present, it means that a fault has been recognized in the wiring or connector of the Control Area Network or in the Fully Integrated Power Module (TIMP), due to an open circuit.
• High CAN bus wires or connectors may be in poor condition.
• Battery voltage may not be sufficient.
• Possibly there are deficiencies in a controller.
• Deficient or sulfated ground on the module.
• Deterioration in the CAN bus harness.
• Outdated module software.

In order to troubleshoot the DTC U0003 OBDII code consider the following:

• Consult the Technical Service Bulletins.
• Using an automotive scanner, try to establish communication with a control module in order to check if there are other network-related codes stored. If so, diagnose the codes in the order retrieved.
• It may be a matter of resetting the software of the faulty module. In some cases, modules can be reprogrammed.
• Check the integrity of the battery, as well as the voltage that sends the same one is within the acceptable parameters. If deficiencies are found in this value, make the required corrections.
• Check the high CAN bus wiring for damage due to burns or wear. If any of the above conditions are found, proceed with repairs.