U1990 – CAN Communication Bus Fault.

The ODBII code U1990 indicates a fault in the CAN (Controller Area Network) communication bus, suggesting a communication issue between modules in the vehicle’s network.

The severity of ODBII code U1990 CAN Communication Bus Fault is generally considered moderate to severe.

Common Causes For: U1988 Lost Communication with the Body Control Module (BCM)”.

• Faulty CAN bus wiring or connectors
• Malfunctioning CAN bus modules
• Short circuits in the CAN bus
• Open circuits in the CAN bus
• Interference from other electrical components
• Corroded or damaged connectors
• Faulty or incompatible aftermarket accessories
• Software or firmware issues in the modules
• Low battery voltage or poor power supply
• Grounding issues in the vehicle’s electrical system

Common misdiagnosis for U1990 CAN Communication Bus Fault.

• Faulty Engine Control Module (ECM)
• Defective Body Control Module (BCM)
• Bad wiring or connectors
• Faulty sensors
• Malfunctioning transmission control module
• Powertrain control module issues
• Battery or charging system problems
• Grounding issues
• Faulty CAN bus transceiver
• Software or firmware issues in modules

Common Troubleshooting Steps

The OBD-II code U1990 indicates a CAN (Controller Area Network) communication bus fault. This code typically suggests that there is a problem with the communication between various modules in the vehicle. Here are some common troubleshooting steps to diagnose and resolve the U1990 code:

• Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Other codes may provide more context about the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors related to the CAN bus. Look for damaged, frayed, or corroded wires and loose connections.
• Pay special attention to the connectors at the ECM (Engine Control Module) and other modules on the CAN bus.
• Check for Short Circuits:
• Use a multimeter to check for short circuits in the CAN bus wiring. Measure resistance between the CAN High and CAN Low wires; they should not be shorted together.
• Test the CAN Bus Voltage:
• Use an oscilloscope or a multimeter to check the voltage levels on the CAN High and CAN Low wires. The typical voltage levels should be around 2.5V when idle and should toggle between 0V and 5V when data is being transmitted.
• Inspect Modules:
• Check the modules connected to the CAN bus for any signs of failure. This includes the ECM, BCM (Body Control Module), ABS module, and others.
• If possible, perform a module reset or reprogramming if the module is suspected to be faulty.
• Check for Interference:
• Look for any aftermarket devices or modifications that may interfere with the CAN bus communication, such as alarms, stereo systems, or other electronic devices.
• Scan for Communication Issues:
• Use a professional-grade scan tool to check if the modules are communicating properly. Some tools can perform a network test to identify which module is not responding.
• Inspect Ground Connections:
• Ensure that all ground connections related to the CAN bus and modules are secure and free of corrosion.
• Check Battery Voltage:
• Ensure that the vehicle’s battery is in good condition and fully charged. Low voltage can cause communication issues.
• Perform a Hard Reset:
• Disconnect the battery for a few minutes to reset the vehicle’s computer systems. Reconnect and see if the code reappears. 1
• Consult Technical Service Bulletins (TSBs):
• Check for any TSBs related to the U1990 code for your specific vehicle make and model. Manufacturers may have specific fixes or updates. 1
• Seek Professional Help:
• If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who specializes in automotive electronics. By following these steps, you should be able to identify and resolve the underlying issue causing the U1990 CAN Communication Bus Fault code.