2025 Audi A5 Engine Warning Lamp On (DTC U041800)

Owners of 2025 Audi A5, Q5, S5, and SQ5 models may notice the "Engine warning lamp (MIL) on" in their instrument cluster. This condition is often accompanied by Diagnostic Trouble Code (DTC) U041800. Audi Technical Service Bulletin (TSB) 2078871/1 addresses this specific issue, which involves an implausible signal from the ABS control module.

Symptoms

Vehicle owners may observe the following:

• The "Engine warning lamp (MIL) on" illuminates on the dashboard.
• Malfunction display symbols related to "emissions control system malfunction display" or "engine management malfunction display (diesel)" may appear.

Fault Codes / DTCs

When scanned, the vehicle's diagnostic system may log the following code:

• DTC: U041800
• Description: "ABS Control Module, implausible signal"
• Symptom Code: 487509
• Diagnostic Address: 812C

Diagnosis and Trigger Conditions

This 2025 Audi A5 engine warning lamp issue is typically triggered when signals from the ABS control unit are provided with a delay. This delay can activate the warning lamp if the electrical system voltage drops below 12V. It's important to note that after a bus sleep cycle, the engine warning lamp may no longer be on, making the complaint difficult to reproduce during a workshop visit.

Important Warnings for Owners

Audi has stated that billing to TSB 2078871/1 is not permitted. This indicates that the service information is for support during work, but specific warranty claims might need to follow other procedures. Additionally, the measures on how to correctly provide the signals and revise the warning messages are currently in development by Audi.

Repair Procedure Summary

For a 2025 Audi A5 engine warning lamp illuminated with DTC U041800, technicians should ensure a 12V power supply is maintained on the vehicle. After confirming adequate voltage, the DTC U041800 should be cleared. The original customer complaint may have been resolved by a bus sleep cycle, but the vehicle should be re-evaluated based on any clear, persistent complaints.

Owner Action

If you experience the "Engine warning lamp (MIL) on" or any related malfunction display messages on your 2025 Audi A5, Q5, S5, or SQ5, it is recommended to visit an authorized Audi service center. While the issue might clear itself after a bus sleep cycle, a professional diagnosis can confirm the presence of DTC U041800 and address the underlying cause. Be aware that the manufacturer's long-term solution for signal provision and warning message revision is still under development.

Source: NHTSA ID: 11022654