U1804 – Data Bus Communication Fault
The ODBII code U1804 indicates a data bus communication fault, meaning there is a problem with the communication between the vehicle’s control modules over the data bus network.
The severity of ODBII code U1804 is moderate.
Common Causes For: U1803 U1803: Data Bus Communication Fault
- Faulty wiring or connectors in the data bus system
- Malfunctioning control modules
- Poor ground connections
- Corroded or damaged connectors
- Interference from aftermarket devices
- Software issues or bugs in the control modules
- Low battery voltage or power supply issues
- Faulty or damaged data bus communication lines
Common misdiagnosis for U1804 U1804: Data Bus Communication Fault
- Faulty ABS module
- Defective engine control module (ECM)
- Malfunctioning transmission control module (TCM)
- Bad wiring or connectors
- Faulty body control module (BCM)
- Issues with the CAN bus system
- Defective powertrain control module (PCM)
- Incorrectly installed aftermarket accessories
- Low battery voltage or weak battery
- Grounding issues
Common Troubleshooting Steps
The OBD-II code U1804 indicates a “Data Bus Communication Fault.” This code typically points to issues with the communication between various modules in the vehicle’s network. Here are some common troubleshooting steps to diagnose and resolve the U1804 code:
- Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Other codes may provide more context or indicate which module is having communication issues.
- Inspect Wiring and Connectors: Visually inspect the wiring and connectors related to the data bus. Look for signs of damage, corrosion, or loose connections. Pay special attention to the connectors of the modules involved in the communication.
- Check the Modules: Identify the modules that are part of the communication network (e.g., Engine Control Module (ECM), Transmission Control Module (TCM), Body Control Module (BCM), etc.). Ensure that they are functioning properly and are powered.
- Test the Data Bus: Use a multimeter or an oscilloscope to test the data bus for proper voltage levels and signal integrity. Check for short circuits or open circuits in the data lines.
- Inspect for Ground Issues: Ensure that all modules have a good ground connection. Poor grounding can lead to communication faults.
- Check for Interference: Look for any aftermarket devices or modifications that may interfere with the data bus communication. This includes alarms, stereo systems, or other electronic devices.
- Perform a Network Scan: If available, use a professional-grade scan tool to perform a network scan. This can help identify which module is not responding or communicating properly.
- Reset the Codes: After performing inspections and repairs, clear the codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns.
- Update Software/Firmware: Check if there are any software updates available for the vehicle’s modules. Sometimes, communication issues can be resolved with a software update.
- Consult Service Manual: Refer to the vehicle’s service manual for specific diagnostic procedures related to the U1804 code. This may provide additional insights or steps tailored to your vehicle model.1
- Seek Professional Help: If the issue persists after performing the above steps, consider seeking help from a qualified mechanic or dealership. They may have specialized tools and knowledge to diagnose complex communication issues. By following these steps, you should be able to identify and resolve the underlying cause of the U1804 code.