2022-2025 Audi Start System Fault TSB 2077631/1

Audi has released Technical Service Bulletin (TSB) 2077631/1 to address an instrument cluster message stating "Engine/power unit start system: fault. Please contact workshop" or "Engine start system: fault. Please contact workshop." This issue is typically accompanied by diagnostic trouble code (DTC) B143C29, indicating an implausible signal from the access/start authorization button. This TSB applies to various 2022-2025 Audi models, including the e-tron, A4, A6, A7, Q5, Q7, and Q8.

The TSB, released on April 16, 2025, clarifies that the Audi start system fault B143C29 often stems from the driver not fully depressing the start/stop button.

Symptoms

Owners of affected Audi vehicles may observe one of the following messages appearing in the instrument cluster:

• "Engine/power unit start system: fault. Please contact workshop"
• "Engine start system: fault. Please contact workshop"

These messages indicate a problem with the vehicle's engine start system, potentially affecting engine operation or the Start/Stop system functionality.

Fault Codes / DTCs

When diagnosing this issue, technicians may find the following diagnostic trouble code stored in the vehicle's systems:

Diagnostic Address	Diagnostic Trouble Code	Fault Symptom	Storage State
0046 - Convenience system central module	B143C29: Access/start authorization button implausible signal	symptom number 65638	Intermittent / static

The DTC B143C29 specifically points to an implausible signal from the access/start authorization button, with symptom number 65638. The convenience system central module (J393, diagnostic address 0046) is the component where this fault is typically logged.

Diagnosis and Technical Background

Audi's technical background for TSB 2077631/1 explains that the DTC B143C29 with symptom number 65638 is triggered when not all positions of the start/stop button are detected after being pressed a certain number of times consecutively. For model years up to 2022, this threshold is 30 presses. For 2023 model year vehicles and newer, the threshold has been increased to 50 presses before the fault is logged.

The primary reason for this Audi start system fault B143C29 is often that the driver does not press the start/stop button completely down. The system interprets these partial presses as an implausible signal, leading to the error message and DTC.

Important Warnings for Owners

• Do not replace the button: If the diagnostic checks confirm that all button positions are detected, it is assumed the button is functioning correctly. The complaint is then attributed to the button not being fully pressed. In such cases, replacing the start/stop button is not necessary and will not resolve the underlying cause.
• Technical Note on Contact 4: Audi explicitly states that contact 4 is not used in this system. An operation will never be shown for contact 4 when the button is pressed, and it should not be included in any diagnostic analysis.

Repair Procedure Summary

For technicians, the TSB outlines a diagnostic procedure. In the convenience system central control unit J393 (diagnostic address 0046), technicians should check the measured value for "entry and start authorization button." This check involves ensuring that all three button positions are detected when the button is pressed all the way down. If the DTC is logged statically but all button positions are detected, it should subsequently become intermittent. If all button positions are detected, the button is considered functional.

Warranty Information

For vehicles outside of warranty, this Technical Service Bulletin is informational only. Warranty claims related to this issue should be submitted in accordance with the Audi Warranty Policies and Procedures Manual. The relevant service number is 9677 and the damage code is 0040. Labor operations may include GFF / Guided Functions (0150 0000), Charge Battery (2706 8950), or potentially replacing the start/stop button (9677 19xx/9677 55xx) if deemed necessary after full diagnosis, though replacement is generally discouraged if the button is functional.

What Owners Should Do

If you experience the "Engine/power unit start system: fault" message or suspect an Audi start system fault B143C29, first ensure you are consistently pressing the start/stop button all the way down. If the issue persists, it is recommended to contact an authorized Audi service center. They can perform the necessary diagnostic checks using TSB 2077631/1 to confirm the cause and advise on any required actions.

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Source: NHTSA ID: 11017659