U0123 – Data bus: yaw rate sensor module – no communication

Reinier

By Reinier (Contact Me)
Last Updated 2016-09-10
Automobile Repair Shop Owner

CodeFault LocationProbable Cause
U0123 Data bus: yaw rate sensor module - no communication
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What Does Code U0123 Mean?

OBD II fault code U0123 is defined as “Lost Communication with Yaw Rate Sensor Module”, or sometimes as “Lost Communication with Yaw Rate Sensor”, and is set when a loss of communication occurs between the Yaw Rate Sensor/Module, and the other control modules that control the ABS, traction control, and stability control systems on a modern vehicle. “Communication” refers to the constant exchange of data between various controllers via the CAN bus (Controller Area Network) system. When the loss of communication exceeds 1 second on most applications, a code will be set and warning lights such as the ABS, Stability Control, and Traction Control will be illuminated. Note that Stability Control and/or Traction Control warning lights may flash. In terms of its operation, the yaw rate sensor/module measures the difference between the intended path, and the actual path the vehicle takes during cornering or violent evasive manoeuvres to avoid obstacles. However, the yaw rate sensor/module and its associated control modules form only one part of the equation that determines, or controls vehicle stability; other information relevant to the equation includes vehicle road speed, throttle position, transmission mode, and in some cases, even the proximity of other vehicles and/or obstacles. Nonetheless, the yaw rate sensor/module is typically inactive when the vehicle is moving in a straight line, and only becomes active when the steering angle changes. The amount of steering input is sent to the yaw rate sensor/module, where this information is compared to the road speed, throttle position and other parameters, such as data on lateral accelerations obtained from an accelerometer. If the yaw rate sensor/module determines that the vehicle is deviating from the intended path (based on the steering angle, road speed, and individual wheel speeds), and that the deviation is likely to cause a dangerous situation such as a skid, it will activate the stability control system to apply selective braking forces to one or more wheels via the ABS system to force the vehicle to follow the intended steering path. Note that in some cases, the stability control system may assume temporary control of both the throttle and transmission until the various systems involved in maintaining vehicle stability deem the vehicle to be under control, or to be following the intended steering angle. The image below illustrates the types of deviations from the intended steering angle the yaw rate sensor/module is intended to identify and correct. In both under -, and over steer conditions, the yaw rate sensor/module activates the stability control system to force the vehicle to follow the intended steering angle as communicated by the steering angle sensor. steering-angle-deviation

What are the common causes of code U0123?

The most common causes of U0123 are the loss of one or more ground connections, and open circuits in the CAN bus system, but to the yaw rate sensor/module in particular. Other possible causes could include the following-
  • Defective yaw rate sensor/module
  • Damaged, burnt, shorted, or corroded wiring and/or connectors
  • Low battery voltages that can damage control modules, including the yaw rate and related sensors/modules. In these cases, other codes that relate to the electrical system will almost certainly be present along with U0123.
  • High system voltages or voltage spikes that can damage control modules, including the yaw rate and related sensors/modules. In these cases, other codes that relate to the electrical system will almost certainly be present along with U0123.
  • Note that while failures of the PCM and other controllers do occur, it is a rare event, and therefore the fault must be sought elsewhere before any controller is replaced.

What are the symptoms of code U0123?

Code U0123 will rarely cause driveability issues, but be aware that depending on the application, the warning light for the ABS system may be illuminated along with those for the traction -, and stability control systems. Also, note that on some applications the traction control and ABS systems may be deactivated while code U0123 is active and unresolved.

How do you troubleshoot code U0123?

WARNING: Since U0123 is one of the few codes that indicate in which part of the CAN bus system a fault has occurred, it might be possible for non-professional mechanics to diagnose and repair this code. However, extreme care must still be taken when diagnosing this code because placing a probe on the wrong connector pin at the wrong time can cause fatal damage to other parts of the CAN bus system. Therefore, it is strongly recommended that the vehicle be referred for professional diagnosis and repair if you do not have a complete understanding of how the CAN bus system works, or of the circuits being tested. Also, take note that generic code readers generally cannot access the CAN bus system, meaning that referring the vehicle for professional diagnosis and repair might be the better option if professional grade diagnostic equipment is not available. NOTE #1: If you have enough confidence in your diagnostic skills to attempt a diagnosis of code U0123, you will require a repair manual that includes complete wiring diagram for the application being worked on, as well as a pin-out chart that clearly indicates the function and color-coding of each wire in every connector in the system under investigation. Attempting a diagnosis of this code unless you have an accurate and valid wiring diagram/pin-out chart, will almost certainly result in a misdiagnosis and secondary damage to the CAN bus system caused by short circuits due to incorrect diagnostic methods. NOTE #2: Before starting an electrical diagnosis of this code, check to make sure that the traction control system has not been deactivated or switched off. On most applications, the traction control warning light will flash when the system is deactivated, which could be interpreted as a fault by inexperienced mechanics, especially in cases where a generic code reader cannot access the CAN bus system to confirm that a fault code is actually present. NOTE #3: On some applications, it may not be possible to clear code U0123 if the steering angle sensor has not been recalibrated after a 4-wheel alignment procedure, or after some types of repair work to the steering system has been completed. Always check that the steering angle calibration is valid, or follow the directions in the manual on the correct procedure to recalibrate the steering angle sensor. TIP: When dealing with code U0123, it is always a good idea to check for TSB’s (Technical Service Bulletins) for the application being worked on. There are many online resources that list TSB’s by make and model, and many hours of diagnostic time (and lots of money) can be saved if you have a known cure for a known issue on the affected application.

Step 1

If the traction control system has not been deactivated manually, and the steering angle sensor is properly calibrated, record all fault codes present, as well as all available freeze frame data. This information can be helpful should an intermittent fault be diagnosed later on.

Step 2

Start the diagnostic procedure by inspecting all associated fuses, and replace any that show signs of discoloration caused by arcing, overheating, or corrosion. NOTE: If any fuses are found that have overheated, make a note of the fuse number(s) to make it easier to trace the affected circuit(s) on the wiring diagram during the next step.

Step 3

Consult the manual to determine the location, routing, function, and color-coding of each wire in each of the affected modules’ control circuit, and prepare to perform a thorough visual inspection of all affected wiring. However, before you start disassembling the vehicle, consult the manual to locate all ground connection points on the vehicle frame. Although all control modules require a sound ground connection to work, some control modules are grounded through the PCM, while others are grounded to the vehicle frame. Since loss of ground is a common cause of code U0123, locate all relevant ground connection points on the vehicle frame and make sure they are sound. If needs be, clean the connection point by sanding the metal surface with coarse sandpaper, and reconnect all ground wires, making sure that all connections and/or fasteners are properly secured. NOTE: Be aware that depending on the application, inspecting wiring could involve removing parts of the dashboard, seats, carpets, and various trim panels.

Step 4

If bad ground connections were found and repaired, clear all codes, and retest the system to see if the code returns. Note that in some cases, you may have to complete a prescribed drive cycle to reset the fault memory.

Step 5

If the code persists, locate all affected control modules and their associated wiring harnesses in order to inspect the wiring for signs of damage, short circuits, open circuits, disconnected wires, and/or corroded wiring and connectors. Note that this inspection requires insulation to be removed from wiring harnesses, so take extreme care to prevent causing damage to wiring where there was none before. If visible damage or problems are found, resist the temptation to repair wiring. Replacing damaged wiring harnesses with OEM replacements is always the better option because it eliminates issues with high resistances and/or poor continuity caused by poorly executed repairs. If repairs/replacements are made, clear all codes and retest the system to see if the code returns. Refer to Step 4. NOTE: In some cases, control modules that were disconnected may have to be reintegrated into the CAN bus system. Be sure to follow the instructions provided in the manual to do this correctly if reintegration is required.

Step 5

If however, no visible damage is found, prepare to perform reference voltage, ground, continuity, and resistance checks on all associated wiring. WARNING: Despite opinions to the contrary, DO NOT disconnect the battery during this step unless the manual specifically states that the battery needs to be disconnected at this point. Disconnecting the battery if it does not need to be disconnected can have unpredictable results at best, and cause the loss of data and memory from several control modules at worst. In any event, if the battery needs to be disconnected, follow the instructions in the manual to the letter, and make sure that a memory saving device is installed as per the instructions provided. Disconnect all controllers from their wiring harnesses before commencing resistance and/or continuity tests to avoid damage the modules. Be aware that this step requires the individual testing of several dozen circuits, and it is easy to test the wrong pin at this point. To make the procedure easier, and safer, test one circuit at a time and always insert the multimeter probe into a connector from the back of the connector. Nevertheless, take extreme care to avoid short circuits, and do NOT attempt this step if you do not have clearly marked pin-out charts for every connector in the circuit being tested. Compare all obtained readings with those stated in the manual, and replace any harness that contains a circuit in which obtained readings deviate from stated values.

Step 6

Some applications have two specialized communication circuits called the CAN C+ (or HSCAN +), and CAN C- (or HSCAN –) circuits, respectively. If these circuits are functional, they will cause a reading to be displayed on the multimeter, but be aware that the displayed values can differ between applications, although the value for the CAN+ circuit is usually around 2.6 volts, while the value for the CAN - circuit is usually about 2.4 volts. Note that on some applications, the value for the CAN – circuit can be as low as 0.5 volt. Note that slight fluctuations of these readings while they are being displayed are normal. Check the manual and/or the wiring diagram to see if the application has these high-speed CAN bus circuits, and follow the directions in the manual on the correct procedure to test them. Compare obtained readings with those stated in the manual, and follow the directions provided in the manual on the correct procedure to test for possible causes if obtained readings do not agree with stated values. Make repairs as required, or replace affected harnesses before testing the circuits again to see if communication has been restored. Refer to Step 4.

Step 7

If all electrical values fall within specification but the code persists, or reappears after having completed several drive cycles, there are two possibilities to consider. The first is that there is likely to be an intermittent fault present that can be extremely challenging even for professional mechanics to find and repair, and the second is that one or more control modules are defective. In both cases, the better option would be to refer the vehicle for professional diagnosis and repair. If an intermittent fault is the problem, large sections of the wiring harness is the best option; if control modules are defective, the replacement(s) need to be programmed to match the specific application, both of which are procedures that is best left to professional technicians.

Codes Related to U0123

Code U0123 refers specifically to a loss of communication with the Yaw Rate Sensor/Module, and as such, there are no directly related codes. As with other “Loss of Communication with ....” codes that run from U0100 to U029A there is no provision for codes indicating intermittent faults- once communication is lost for a period of time specified by the manufacturer, the relevant “Loss of Communication with ....” code will be set.