2016-2025 Audi Engine Start System Fault Message TSB

Owners of various 2016-2025 Audi models, including the Audi e-tron engine start system fault, may encounter an instrument cluster message indicating an issue with the engine or power unit start system. This Technical Service Bulletin (TSB) 2077631/1, released on April 16, 2025, provides diagnostic and repair information for this specific condition.

Symptoms

Customers may observe one of the following messages displayed in the instrument cluster:

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

These messages indicate that the vehicle's starting system is experiencing an issue, prompting the driver to seek service. Other related complaints may include the engine start function being partially out of order, issues with start authorization or immobilizer, or malfunction display symbols activating with or without cause.

Fault Codes / DTCs

When diagnosing the reported symptoms, technicians may find the following Diagnostic Trouble Code (DTC) stored in the Comfort System Central Control Module (-J393-, diagnostic address 0046):

Diagnostic Trouble Code	Description	Fault Symptom	Storage State
B143C29	Access/start authorization button implausible signal		Intermittent
B143C29	Access/start authorization button implausible signal		Static

This TSB specifically applies when DTC B143C29 is stored in conjunction with symptom number 65638.

Diagnosis / Trigger Conditions

The DTC B143C29, with symptom number 65638, indicates that not all positions of the access/start authorization button were detected when it was pressed a specific number of times in a row. For models up to 2022, this threshold was 30 presses. For 2023 model year vehicles and newer, the threshold has been increased to 50 presses. This condition can affect the Audi e-tron engine start system fault and other models.

The primary reason for this implausible signal is often that the customer did not press the start/stop button all the way down during these operations. The system interprets these incomplete presses as an issue, even if the ignition button itself is functioning correctly.

Production Solution

For 2023 model year vehicles and newer, Audi has implemented a production change. The threshold at which the event memory entry for DTC B143C29 is logged has been increased from 30 presses to 50 presses. This adjustment aims to reduce instances of the fault message appearing due to minor, incomplete button presses.

Repair Procedure Summary

If a customer reports this issue, technicians should perform the following steps:

1. Access the convenience system central control unit J393 (diagnostic address 0046).
2. Check the measured value for "entry and start authorization button" while pressing the button all the way down. Verify that all three button positions are detected.
3. Important: Audi does not use