U0126 OBD-II: Lost Communication With Steering Angle Sensor Module

What does code U0126 mean?

Code U0126 stands for Lost Communication with Steering Angle Sensor (SAS) Module.

Older vehicles use a hydraulic power steering pump to provide the driver with power steering. This makes the steering wheel easy to turn. Many modern vehicles, however, are equipped with electric power steering.

Power steering makes the steering wheel easy to turn.

A typical electric power steering system consists of the following components:

• Control module
• Steering angle sensor (SAS)
• Torque sensor
• Steering column-mounted electric motor
• Rack and pinion assembly

The control module is computer that monitors and controls the system. The steering angle sensor detects the position of the steering wheel. On the other hand, the torque sensor measures steering column twist. The power steering control module uses this sensor information to determine control of the electric motor. The motor helps turn the steering gear pinion turn the rack from left to right, according to turning of the steering wheel.

In some cases, the SAS is built into the control module. It is then referred to as a SAS control module, instead of a sensor. The SAS module communicates with other modules throughout the vehicle via the Controller Area Network (CAN) bus. The CAN bus consists of two lines: CAN High and CAN Low. The CAN High bus has a data rate of 500k bits/second, whereas CAN Low Communicates at a data rate of 125k bits/second. Two terminating resistors are located at the ends of the CAN bus.

Code U0126 indicates the SAS module is not receiving or transmitting messages on the CAN bus.

U0126 symptoms

• Illuminated warning lights
• SAS-related performance issues

Common causes for U0126

Code U0126 is typically caused by one of the following:

• A dead battery
• A faulty SAS module
• A problem with SAS module circuit
• A problem with the CAN bus

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How to diagnose and repair U0126

Perform a preliminary inspection

Sometimes U0126 can pop up intermittently, or it can result from a dead battery. This is especially true if the code is a history code and not current. Clear the code and see if it returns. If it does, the next step is to perform a visual inspection. A trained eye can check for issues such as broken wires and loose connections. If a problem is found, the issue should be repaired and the code cleared. If nothing is discovered, check for technical service bulletins (TSBs). TSBs are recommended diagnostic and repair procedures put out by the vehicle manufacturer. Finding a related TSB can greatly reduce diagnostic time.

Check the battery

The SAS module is a computer and computers need proper voltage to operate. Check the battery and charging system and repair as needed. Clear the codes and see if they return.

Check for other DTCs

Additional diagnostic trouble codes (DTCs) may indicate problems elsewhere that are affecting SAS module operation. For example, multiple communication DTCs may indicate a problem with the CAN network. Any additional DTCs should be addressed prior to diagnosing U0126.

If multiple communication DTCs are stored, diagnosis should start with the CAN bus. The bus can be checked for typically electrical defects, such as opens and shorts. CAN diagnosis usually begins at the datalink connector with a DMM or breakout box. Pin 6 of the connector is CAN High and pin 14 is can low. From there, further testing and repair of the CAN bus can be completed as needed.

Check for a faulty control module

If U0126 is the only DTC stored, the SAS module itself should be checked. The easiest was to start this process is by attempting to communicate with the SAS using a diagnostic scan tool. Once connected to the vehicle, the tool acts like just another module on the network. It can be used to address the SAS module. If the module does not respond, there is a problem with it.

Before condemning the module, it's important to check its circuit. Like any other electronic device, the SAS module must have proper power and ground. This can be done with a DMM.

If the module's circuit it good, yet it still won't communicate, it is probably faulty. Before replacing the module, however, its software should be checked. Often times a module can be reprogrammed instead of replaced if there's an available TSB or update.

Note: In some cases, the SAS sensor can be removed from the control module and serviced separately.

Other diagnostic codes related to U0126

All the 'U' codes are network communication codes. Codes U0100 to U0300 are lost communication with XX module codes.

Code U0126 technical details

This code is typically monitored when the ignition is on and battery voltage is within a specific range.