Navigating the complexities of modern vehicle diagnostics often involves deciphering OBDII (On-Board Diagnostics II) codes. Among these, code U0126, “Lost Communication with Steering Angle Sensor (SAS) Module,” is a communication fault code that can impact your vehicle’s steering and stability systems. As an expert at Autel France, understanding this code is crucial for effective vehicle repair. This article delves into the specifics of U0126, providing a comprehensive guide to its symptoms, causes, diagnosis, and potential fixes.
To fully grasp the significance of U0126, it’s essential to understand the role of the Steering Angle Sensor (SAS) and the system it operates within. Many contemporary vehicles have transitioned from traditional hydraulic power steering to Electric Power Steering (EPS) systems. EPS offers enhanced fuel efficiency and greater control, and the SAS is a critical component within these systems.
Understanding Electric Power Steering (EPS) systems is key to diagnosing U0126, which often involves the Steering Angle Sensor within these modern steering setups.
A typical EPS system integrates several key components:
- Control Module (EPS CM): The brain of the system, processing data and controlling the electric motor.
- Steering Angle Sensor (SAS): This sensor monitors the steering wheel’s position and rate of turn, crucial for stability and steering assist functions. In some designs, the SAS is integrated into the control module itself, referred to as the SAS module.
- Torque Sensor: Measures the force applied to the steering wheel by the driver, providing input for the EPS system to determine the level of power assist needed.
- Electric Motor: Mounted on the steering column, this motor provides the power assist to make steering easier.
- Rack and Pinion Assembly: The mechanical linkage that translates steering wheel input into wheel movement.
The SAS module is vital for vehicle systems like Electronic Stability Control (ESC) and power steering. It communicates steering wheel angle information to other vehicle modules via the Controller Area Network (CAN) bus. The CAN bus is a communication network within the vehicle, allowing various modules to share data. It utilizes two lines, CAN High and CAN Low, operating at different data speeds. Terminating resistors at each end of the bus ensure signal integrity.
Code U0126 arises when the SAS module fails to communicate effectively on the CAN bus. This communication loss disrupts the data flow necessary for proper functioning of systems relying on steering angle information.
Symptoms of OBDII Code U0126
When your vehicle logs a U0126 code, you may observe several symptoms, indicating a problem with the SAS module’s communication:
- Illuminated Warning Lights: The most common symptom is the activation of warning lights on your dashboard. These may include the power steering warning light, ABS (Anti-lock Braking System) light, ESC/Traction Control light, or a general check engine light. The specific lights will depend on the vehicle make and model and which systems are affected by the loss of SAS signal.
- Power Steering Issues: You might experience problems with the power steering assist. This can range from intermittent loss of power assist to a complete lack of power steering, making the steering wheel hard to turn, especially at low speeds.
- Stability Control Problems: Since the SAS input is critical for ESC and traction control systems, a U0126 code can lead to issues with these systems. You may notice that the ESC or traction control system is not functioning correctly, particularly during cornering or in slippery conditions.
- Other System Malfunctions: In some cases, depending on the vehicle’s design and how interconnected its systems are, a U0126 code could potentially affect other systems that rely on CAN bus communication.
Common Causes of U0126
Several factors can lead to a U0126 code. Identifying the root cause is essential for effective repair:
- Low Battery Voltage or Dead Battery: The SAS module, being an electronic component, requires stable and sufficient voltage to operate correctly. A weak or dead battery can cause communication issues and trigger a U0126 code, especially during vehicle start-up when voltage dips.
- Faulty Steering Angle Sensor (SAS) Module: The SAS module itself may be defective. Internal electronic failures or sensor malfunctions can prevent it from communicating properly on the CAN bus.
- SAS Module Circuit Issues: Problems in the wiring and circuits connected to the SAS module are a common cause. This includes:
- Open circuits: Broken or disconnected wires in the power, ground, or CAN bus lines to the SAS module.
- Short circuits: Wires shorting to ground or to each other, disrupting signal flow.
- High resistance: Corrosion or loose connections increasing resistance in the circuits, weakening signals.
- CAN Bus Problems: Issues within the CAN bus network itself can disrupt communication between modules. This could be due to:
- CAN bus line faults: Breaks, shorts, or excessive resistance in the CAN High or CAN Low wires.
- Terminating resistor issues: Faulty or missing terminating resistors can cause signal reflection and communication errors across the CAN bus.
- Software or Programming Errors: In rare cases, software glitches within the SAS module or related control modules can lead to communication problems.
Diagnosing and Repairing U0126
Diagnosing U0126 requires a systematic approach. Here are steps a professional technician would typically follow:
1. Preliminary Inspection and Code Verification:
- Initial Scan: Use an OBDII scan tool to confirm the presence of U0126 and check for any other related DTCs. Note if U0126 is current or historical.
- Clear Codes and Retest: Clear the U0126 code and any other stored codes. Then, operate the vehicle to see if the code returns. Intermittent issues or codes triggered by a temporary low voltage situation might not reappear.
- Visual Inspection: Carefully inspect the wiring and connectors associated with the SAS module. Look for:
- Damaged wiring: Frays, breaks, or rodent damage to wires.
- Loose or corroded connectors: Ensure connectors are firmly seated and free of corrosion.
2. Battery and Charging System Check:
- Battery Voltage Test: Use a multimeter to check the battery voltage. It should be within the manufacturer’s specified range (typically around 12.6 volts at rest and around 14 volts when the engine is running).
- Charging System Test: Verify the alternator is charging correctly. A faulty charging system can lead to low voltage issues and communication problems.
3. Check for Other DTCs and CAN Bus Diagnosis:
- Review All DTCs: Note any other DTCs present, especially other communication codes (U-codes). Multiple communication codes can point towards a broader CAN bus issue.
- CAN Bus Testing: If multiple communication codes are present, CAN bus diagnosis is crucial. This often involves:
- Datalink Connector (DLC) Check: Access the DLC (OBDII port) and use a multimeter or oscilloscope to test the CAN bus signals at pins 6 (CAN High) and 14 (CAN Low).
- CAN Bus Circuit Testing: Check for continuity, shorts to ground, and shorts to voltage in the CAN High and CAN Low circuits.
- Terminating Resistor Check: Verify the presence and correct resistance of the CAN bus terminating resistors.
4. SAS Module Circuit Testing:
- Power and Ground Check: Using a wiring diagram for your specific vehicle, identify the power and ground circuits for the SAS module. Use a multimeter to confirm:
- Power Supply: The SAS module is receiving the correct voltage.
- Ground Connection: A good ground connection is present.
- Circuit Integrity Testing: Perform continuity tests on the wiring between the SAS module and the vehicle’s computer or other relevant modules to rule out open or high resistance circuits.
5. SAS Module Communication Test and Potential Replacement:
- Scan Tool Communication: Use a professional-grade scan tool to attempt to communicate directly with the SAS module. If the scan tool cannot establish communication, even after verifying power and ground, it suggests a faulty SAS module.
- Module Reprogramming/Software Update: Before replacing the SAS module, check for any Technical Service Bulletins (TSBs) or software updates from the vehicle manufacturer. In some cases, reprogramming the module with updated software can resolve communication glitches.
- SAS Module Replacement: If all circuit tests are satisfactory and the module still fails to communicate, replacement of the SAS module may be necessary. After replacement, programming or calibration of the new module is often required using a scan tool to ensure correct system operation.
6. Professional Assistance:
Diagnosing CAN bus and communication issues can be complex and requires specialized tools and knowledge. If you are not comfortable performing these diagnostic steps, it is best to seek assistance from a qualified automotive technician. Find a reputable repair shop in your area for accurate diagnosis and repair.
Related OBDII Codes
U0126 is part of the broader family of ‘U’ codes, which indicate network communication issues within the vehicle. Other related codes include:
- U0100 – Lost Communication With ECM/PCM: Indicates a loss of communication with the Engine Control Module (ECM) or Powertrain Control Module (PCM), the main computer controlling engine and transmission functions.
- U0121 – Lost Communication With ABS Control Module: Signifies a communication failure with the Anti-lock Braking System (ABS) control module.
- U-codes (U0001-U0300 range): Generally represent various lost communication faults with different modules throughout the vehicle’s network.
Understanding Obdii Code U0126 and its diagnostic process is crucial for effectively addressing communication issues in modern vehicles. By following a systematic approach and utilizing the right tools, technicians can accurately pinpoint the root cause and restore proper system functionality, ensuring vehicle safety and performance.
