2025-2026 Audi S5, SQ5, A6 P029900 Underboost TSB

Owners of certain 2025-2026 Audi S5, SQ5, and A6 vehicles may experience a "Drive System fault" or an "exhaust emissions warning lamp is illuminated in the instrument cluster", along with a "MIL on" (Malfunction Indicator Lamp). These symptoms are often accompanied by a noticeable slight loss of performance. This condition is linked to Diagnostic Trouble Code (DTC) P029900, specifically "Turbo/Super Charger Underboost", which is stored in the Engine Control Unit (J62). Audi has released Pending Service Solution (PSS) 2079454/3 to address this concern. If you own a 2025-2026 Audi A6 P029900 issue, this bulletin provides crucial information.

Symptoms

If you own a 2025-2026 Audi S5, SQ5, or A6, you might observe the following:

• A "Drive System fault" message displayed.
• The "exhaust emissions warning lamp is illuminated in the instrument cluster".
• The "MIL on" (Malfunction Indicator Lamp) is active.
• A slight loss of engine performance.

These symptoms point towards an issue with the vehicle's engine management system, specifically related to charge pressure.

Fault Codes / DTCs

When diagnosing this issue, technicians will find the following Diagnostic Trouble Code (DTC) stored in the Engine Control Unit (J62, address word 0001):

Code	Description	Symptom	Condition
P029900	Turbo/Super Charger Underboost	34203	static/intermittent

This DTC indicates that the engine's turbocharger or supercharger is not producing the expected boost pressure.

Diagnosis / Trigger Conditions

The root cause of the "Turbo/Super Charger Underboost" condition and the associated DTC P029900 is identified as a software issue within the engine control unit (address 0001) related to charge pressure diagnostics. Owners of a 2025-2026 Audi A6 P029900 fault should be aware of this underlying cause. It's important to note that this complaint typically does not occur during normal vehicle operation. Generally, a low charge level condition is often observed during extended stationary periods, such as during vehicle transportation or while the vehicle is at the workshop.

Important Warnings for Owners

Audi has provided specific instructions regarding this issue. Owners should be aware of the following:

• No immediate repair needed: Audi states that "no repairs are necessary at this point." The matter is under review, and customers will be advised if any action is determined to be needed. A resolution is expected by the end of the 3rd quarter of 2026, though this timing is "subject to change."
• Do not replace components: Audi explicitly advises, "Do not replace any components for this condition since this will not resolve the customer's concern." The issue is software-related.
• PSS applicability: This Pending Service Solution (PSS) may apply to vehicles still within the new model launch repair authorization period.

Repair Procedure Summary

For vehicles experiencing the "Turbo/Super Charger Underboost" condition and storing DTC P029900, the current procedure for Audi workshops involves monitoring and documentation rather than immediate physical repair. If you are dealing with an Audi A6 P029900 issue, technicians are instructed to explain to customers that the issue is under review and that no repairs are currently necessary. Crucially, no components should be replaced for this condition. For vehicles still in the launch phase, workshops must create a web ticket with the Technical Assistance Center (TAC) per the repair authorization. They must also enter the vehicle into the PSS database and reference TSB 2079454/3 in the first line of the TAC case. This process helps Audi gather data for a future solution.

Warranty Information

For this issue, Audi specifies the following warranty claim details under PSS 2079454/3:

• Claim Type: If the vehicle is outside of any warranty, this Technical Service Bulletin is informational only.
• Service Number: 2470
• Damage Code: 0055
• Labor Operations: "GFF/ Guided Functions" with operation codes "0150 0060" (time stated on the diagnostic protocol) and "0150 0010" (See SRT with associated operations).
• Claim Comment: "As per TSB 2079454/3". All warranty claims must adhere to the Audi Warranty Policies and Procedures Manual and are subject to audit.

Required Tools

To diagnose and process this issue, workshops require specific equipment:

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

Revision History

This bulletin, Transaction No. 2079454/3, has undergone several revisions:

• Revision 3: "Revised Service" (updated timing for analysis results).
• Revision 2 (10/07/2025): "Revised header (Add Model)".
• Revision 1 (09/30/2025): "Initial publication".

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Source: NHTSA ID 2079454/3