|Code||Fault Location||Probable Cause|
|U1123|| SCP (J1850) Invalid or Missing Data for Odometer |
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|VNT control unit, wiring, ECU, battery voltage|
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What Does Code U1123 Mean?
Audi, Nissan, and Volkswagen manufacturers define U1123 as SCP (J1850) Invalid or missing data for Odometer. The code is triggered due to a lack of communication or disconnection between controls and components that could affect the odometer. The most possible causes of this code include a malfunction in the VNT (Variable Nozzle Turbine) of the control unit and short circuits in communication wiring between these control units and the ECU.
U1123 is related to the Serial Corporate Protocol (SCP), also called the J1850. The J1850 is a standard protocol adopted by the US for Class B networks. It is defined as a system that transfers data between nodes to reduce redundant elements. It is one of the numerous communications protocols used by different auto manufacturers. The adoption of the SCP (J1850) makes communication between the control modules and other vehicle components possible by using BUS communication.
The code also refers to the odometer which measures the distance that is displayed on the dashboard and cannot be reset. The Odometer is controlled and regulated by modules like the ECM. Once there is a communication fault to the odometer, U1123 will be triggered.
Note: I recommend inspecting the harness and connection for corrosion in diagnosing this code. Also, check for damaged pins and wiring. Verify the voltage to the ECU and flash its software and update it if possible.
Where is the U1123 sensor located?
The ECU of a Volkswagen is usually located above the master cylinder in a black box casing. The unit is in constant communication with the control components of your vehicle, and many times short wire connection between the circuits and these modules could cause a lack of communication and hence trigger the code.
The odometer is found visibly on the car dashboard and constantly displays the distance traveled by the vehicle.
What are the common causes of code U1123?
The U1123 code can be caused by anything that will cause the Communication Bus to fail. It can also be caused by anything that can disrupt the communication between the various communication units. It would be best to inspect the communication or CAN Bus for problems once you get the code or a warning light regarding this code.
Other factors that could cause the U1123 trouble code include:
- Malfunction in the VNT control unit
- Short/ open circuit in communication wiring between ECU and control unit.
- Faulty connection to the Anti-lock brake Module (ABS)
What are the symptoms of code U1123?
The U1123 will come with obvious symptoms that could easily be traced to the code. In most cases, you will first notice the problem in the Odometer. A failed Odometer system is an obvious symptom of this code. Below are some of the obvious signs of the U1123 code.
- Triggered check engine light
- Failed speedometer
- Continuous flashing of the O/D light
Codes Related to U1123
The following are some related codes that may appear with the U1123 fault code on the OBDII scanner.
Another SCP (J1850) code is related to the Hybrid Electronic Cluster (HEC). This is when the PCM of a vehicle can not successfully communicate with the HEC. This code is most likely to come up with the U1123 code.
This code also has to do with the CAN bus lines being faulty. Once the CAN Bus cannot foster communication, you will most likely get this trigger code.
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