2025-2026 Audi MIL On: DTC U041800 (TSB 2081024/1)

Symptoms

Owners of certain 2025-2026 Audi vehicles may observe that the "check engine light (MIL) is/was on" in their instrument cluster. This warning light, also known as the Malfunction Indicator Lamp, signals a potential issue detected by the vehicle's onboard diagnostic system. The presence of the Audi A6 U041800 fault code is directly linked to this symptom, indicating a specific underlying problem.

Fault Codes / DTCs

When diagnosing this condition, service technicians will typically find the following diagnostic trouble code (DTC) stored in the vehicle's systems:

Code	Description	Symptom Code	Diagnostic Address
U041800	"U041800 Brake electronics control unit implausible signal"	487509	812C

This specific DTC points to an implausible signal originating from the brake electronics control unit, which is identified by diagnostic address 812C.

Diagnosis and Trigger Conditions

Audi's workshop findings confirm that customer reports of the check engine light are plausible. A key characteristic of this issue is its intermittent nature: after a period of CAN bus sleep, the warning light may no longer be displayed and can be difficult to reproduce during a workshop visit. The underlying technical cause for the Audi A6 U041800 issue is that signals from the Anti-lock Braking System (ABS) control unit are being provided with a delay, which subsequently triggers the engine warning message.

Production Solution Status

As of the release date of Technical Service Bulletin (TSB) 2081024/1 on February 12, 2026, a permanent production solution for the delayed ABS control unit signals is still under development. Audi anticipates that a definitive solution will be available by the end of the second quarter of 2026. It is important to note that this timeline is subject to change as development progresses.

Important Warnings for Owners

If your 2025-2026 Audi is experiencing a check engine light with the Audi A6 U041800 DTC, it is crucial to understand the manufacturer's current guidance. Audi explicitly advises: "Do not replace any components for this condition since this will not resolve the customer's concern." This instruction is intended to prevent unnecessary part replacements and associated costs, as a permanent fix is forthcoming.

Furthermore, this TSB is informational only and is not applicable to any Audi Warranty for this specific condition. Any additional work performed on the vehicle to address other unrelated DTCs or issues must be billed separately from this bulletin.

Dealer Service Procedure Summary

For owners experiencing this condition, the recommended course of action is to visit an authorized Audi service center. Technicians will perform a diagnosis according to the instructions outlined in TSB 2081024/1. If the vehicle's condition matches the description in the TSB, the technician will explain to the customer that a solution is expected by the end of Q2 2026 and that no physical repairs are necessary at this point for the U041800 fault.

During the service visit, dealers are required to:

• Create a PSS (Pending Service Solutions) record in the PSS application, accessible through the Pending Service Solutions link in Audi Now (Service | AU-US).
• Delete the DTC U041800 from the vehicle's memory. It is noted that the customer's original complaint may have already been resolved by a period of CAN bus sleep.
• Ensure that the vehicle is receiving stable 12V power and eliminate any potential sources of current draw. After these steps, the vehicle should be reassessed for any apparent issues and other DTCs in all control units, with necessary repairs performed for those separate issues.

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Source: NHTSA ID: 11029431, Transaction No.: 2081024/1