U1203 – Lost Communication with the Anti-lock Brake System (ABS) Control Module.

The ODBII code U1203 indicates that there is a loss of communication between the vehicle’s main control module and the Anti-lock Brake System (ABS) control module, which may affect the ABS functionality.

The severity of ODBII code U1203 is generally considered moderate to severe.

Common Causes For: U1202 U1202: “Speed Control Module Communication Loss”

• Faulty ABS control module
• Damaged wiring or connectors
• Corroded connectors
• Blown fuse
• Faulty vehicle speed sensor
• Communication network issues (CAN bus problems)
• Low battery voltage
• Software issues or updates needed in the ABS module

Common misdiagnosis for U1203 Lost Communication with the Anti-lock Brake System (ABS) Control Module.

• Faulty ABS Control Module
• Wiring issues or damaged connectors
• Faulty wheel speed sensors
• Issues with the Engine Control Module (ECM)
• Faulty brake pedal position sensor
• Low battery voltage or charging system issues
• Corroded or loose ground connections
• Faulty diagnostic tools or software errors
• Incorrectly installed or malfunctioning aftermarket components
• Other communication network issues (e.g., CAN bus problems)

Common Troubleshooting Steps

When dealing with the OBD-II code U1203, which indicates “Lost Communication with the Anti-lock Brake System (ABS) Control Module,” there are several common troubleshooting steps you can follow to diagnose and potentially resolve the issue. Here’s a structured approach:

• Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Other codes may provide more context or indicate related issues.
• Inspect the ABS Control Module: **Visual Inspection: Check the ABS control module for any visible damage, corrosion, or loose connections.
• **Connector Check: Ensure that the electrical connectors to the ABS module are secure and free of corrosion or dirt.
• Check Wiring and Connections: Inspect the wiring harness leading to the ABS module for any signs of wear, fraying, or damage.
• Look for any broken or shorted wires that could interrupt communication.
• Test the ABS Module: If possible, perform a bench test on the ABS control module to ensure it is functioning correctly.
• If you have access to a known good ABS module, consider swapping it temporarily to see if the issue resolves.
• Check Power and Ground: Verify that the ABS module is receiving the correct voltage and ground. Use a multimeter to check for proper power supply and ground connections.
• Inspect the CAN Bus: The ABS module communicates over the CAN (Controller Area Network) bus. Check for any issues with the CAN bus wiring or connections.
• Use a scan tool to monitor the CAN bus for communication errors.
• Look for Intermittent Issues: Sometimes, communication issues can be intermittent. Pay attention to when the code appears (e.g., during specific driving conditions) and check for any patterns.
• Check for Software Updates: Verify if there are any software updates available for the ABS module or the vehicle’s ECU. Sometimes, manufacturers release updates to fix communication issues.
• Clear Codes and Test Drive: After performing checks and repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the ABS system for your specific vehicle make and model. Manufacturers may have documented solutions for known issues.1
• Seek Professional Help: If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with ABS systems and advanced diagnostic tools. By following these steps, you should be able to identify the root cause of the U1203 code and take appropriate action to resolve the communication issue with the ABS control module.