2025 Audi A5/S5 Steering Fault B200042 TSB

Owners of 2025 Audi A5 and S5 models may encounter a "Steering fault" message accompanied by a yellow warning lamp in the instrument cluster. This condition, specifically identified by the diagnostic trouble code (DTC) B200042, indicates a control module malfunction related to the steering system. Audi has released Technical Service Bulletin (TSB) 2079733/2 to provide guidance to technicians on diagnosing and resolving this issue.

This TSB, identified as Transaction No. 2079733/2, was initially published on October 22, 2025, and revised on December 18, 2025. The revision added more models to the condition table and updated warranty information. The core problem stems from a software issue affecting the internal memory layout of the steering control module, leading to the "Control module faulty B200042" error.

Symptoms You Might Notice

The primary symptom reported by vehicle owners is the illumination of a yellow steering warning lamp in the instrument cluster. This warning typically appears after a software update or a workshop visit. If you own a 2025 Audi A5 or S5 and observe this warning, it indicates that your vehicle may be experiencing the steering fault B200042.

Fault Codes and Technical Identifiers

When diagnosed by a technician, the steering fault B200042 is logged under diagnostic address 0044. This DTC may be accompanied by symptom codes 5243138 or 13631746, which further specify the nature of the internal memory layout issue. These codes help technicians pinpoint the exact problem and apply the correct resolution.

Technical Background of the Issue

The root cause of the "Control module faulty B200042" steering fault is a software issue. Specifically, it relates to the internal memory layout within the steering control module. This type of software anomaly can lead to incorrect operation or reporting of faults within the system, even if no hardware component is physically damaged. Audi has implemented production solutions for newer vehicles, optimizing the internal memory layout for Audi A5 (FU) models from September 2, 2025, onward, and other e-tron models from later dates.

Repair Procedure Summary

To resolve the steering fault B200042, technicians are instructed to perform a software update. This update is detailed in a separate document, TSB 2079690, titled "00 Combined software update 03.10.00/C (28.13.01) KD2." The procedure involves connecting a battery charger to maintain stable voltage during the update process. The software update aims to correct the internal memory layout issue, thereby eliminating the steering fault B200042.

The repair process typically includes preliminary and follow-up work, such as allowing for a bus sleep cycle and performing calibration drives. These steps ensure that the new software is correctly integrated and the steering system functions as intended. The labor operation for this software update is identified as 0151 0010, with a fixed rate operation 0151 0040 for the complete update process. In cases where a flash abort occurs, an additional labor operation 0150 9999 is available for additional attempts.

Important Warnings for Owners

It is crucial for owners to understand the warranty implications of this Technical Service Bulletin 2079733/2. The TSB explicitly states: "If the vehicle is outside of any warranty, this Technical Service Bulletin is informational only." This means that if your 2025 Audi A5 or S5 is no longer covered by its original warranty, you may be responsible for the cost of the software update. Always confirm your warranty status with an authorized Audi dealer.

What Owners Should Do

If you own a 2025 Audi A5 or S5 and observe the yellow steering warning lamp or the "Control module faulty B200042" message, you should contact your authorized Audi dealer. Explain the symptoms you are experiencing and mention Technical Service Bulletin 2079733/2. The dealer will be able to diagnose the issue using the specified DTC B200042 and perform the necessary software update. It is recommended to schedule an appointment promptly to ensure your vehicle's steering system is functioning optimally.

Source: NHTSA ID 11027410