2025-2026 Audi A5 / Q5 Engine MIL On DTC P029900 TSB

Revision History

This Technical Service Bulletin (TSB) 2079454/2 has undergone revisions since its initial publication. Revision 1 was initially published on September 30, 2025. Revision 2 updated the header to add specific models to the bulletin's scope.

Symptoms

Owners of affected 2025-2026 Audi A5 and Q5 vehicles equipped with the EA839evo V6 TFSI engine may observe several indicators pointing to this issue. The most prominent symptom is the illumination of the Malfunction Indicator Lamp (MIL), commonly known as the 'Check Engine' light, in the instrument cluster. This is often accompanied by a message indicating a "Drive System fault". Additionally, the "exhaust emissions warning lamp is illuminated in the instrument cluster." Owners may also notice "A slight loss of performance noticeable" while driving.

Fault Codes / DTCs

When diagnosing this issue, workshops will find a specific Diagnostic Trouble Code (DTC) stored in the Engine Control Unit (J62), which is addressed as word 0001. The presence of this code is a key indicator of the underlying problem.

Code	Description	Symptom	Module
P029900	Turbo/Super Charger Underboost	34203	Engine Control Unit, J62 (0001)

This DTC is typically recorded as a static/intermittent fault.

Diagnosis and Trigger Conditions

This Audi P029900 MIL issue is specifically linked to certain environmental conditions. The Technical Service Bulletin 2079454/2 explicitly states that this TSB "only applies if the intake temperature is >65°C". This means that the fault is most likely to occur and be diagnosed when the vehicle is operating in high ambient temperature conditions, leading to elevated intake air temperatures. The complaint generally does not occur during normal vehicle operation but can manifest during extended stationary periods, such as during transportation or while the vehicle is at the workshop, due to a low charge level.

Technical Background

The root cause of the "Turbo/Super Charger Underboost" condition and the resulting Audi P029900 MIL warning is identified as a "Software issue (engine control unit, address 0001) with charge pressure diagnostics." This software anomaly primarily triggers the complaint when the vehicle experiences "high ambient temperatures." There is currently no production solution implemented for this issue.

Important Warnings and Owner Information

Audi has provided specific instructions for addressing this issue, and there are critical points for owners to understand:

• No Component Replacement: "Do not replace any components for this condition since this will not resolve the customer's concern." This TSB clarifies that the issue is software-related, and replacing hardware will not fix the problem.
• Resolution Under Review: Owners will be advised if any action is determined to be needed, with a result expected "by the end of the 4th quarter of 2025 (subject to change) and that no repairs are necessary at this point." This means a definitive fix is still being developed.
• New Model Launch Period: "This PSS may apply to vehicles still within the new model launch repair authorization period!" For vehicles in this phase, workshops must create a web ticket with the Technical Assistance Center (TAC) for repair authorization and enter the vehicle into the PSS database, referencing TSB 2079454/2 in the TAC case.

Warranty Information

For vehicles experiencing the Audi P029900 MIL issue, warranty claims are handled according to specific guidelines. The claim type is generally applicable if the vehicle is within its warranty period; otherwise, the bulletin serves as informational guidance. The Service Number associated with this TSB is 2470, and the Damage Code is 0055.

Labor operations for this service include:

• GFF/ Guided Functions (0150 0060): Time stated on the diagnostic protocol.
• GFF/ Guided Functions (0150 0010): See SRT with associated operations.

All warranty claims must adhere to the Audi Warranty Policies and Procedures Manual and are subject to review by Audi Warranty. The claim comment should reference "As per TSB 2079454/2".

Required Tools

To diagnose and address this condition, Audi workshops will utilize specific diagnostic equipment:

• VAS 6160/VAS 6150: These are specialized VAS testers.
• ODIS (Windows 10): The VAS testers must be running the current version of the Offboard Diagnostic Information System (ODIS) software on a Windows 10 operating system.

NHTSA ID: 10252577