2021 Audi Models Rear Window Defogger Non-Operational

Symptoms

Owners of affected 2021 Audi vehicles may experience the following symptom related to the rear window defogger:

• "The rear window defog button will light up for a second when pressed, then immediately turn off."

This indicates that the system is not engaging properly, preventing the rear window from defogging.

Technical Background

According to Audi, the underlying cause of the Audi e-tron rear defogger non-operational issue is that the comfort system central control module, identified as J393 (address word 0046), becomes locked in a loop and requires a reset. Audi is actively developing a software solution to prevent this condition in future production.

Fault Codes / DTCs

This particular issue does not typically store Diagnostic Trouble Codes (DTCs) in the vehicle's memory under normal circumstances. However, it's important to note that performing the output test as part of the diagnostic procedure will temporarily create DTCs in the J393 control module. These must be cleared after the test is complete and before any further diagnostics.

Diagnosis and Trigger Conditions

To diagnose this issue, technicians are advised to first attempt to reproduce the customer's concern. If the rear window defogger functions correctly, this Technical Service Bulletin (TSB) does not apply. For the rear window defog feature to operate, the ambient temperature must be below 95°F (35°C), and the engine must be running.

Repair Procedure Summary

The repair procedure involves using the ODIS diagnostic system to perform an output test on the rear window defogger. This process effectively resets the control module that has become locked in a loop.

1. Verify Concern: Confirm the rear window defogger button lights up briefly and then turns off.
2. Access ODIS: Connect to the ODIS system and navigate to the comfort system central control module, J393 (address word 0046).
3. Select Guided Functions: Right-click on the 0046 Control Module and select "Guided Functions."
4. Choose Output Diagnostic Test Mode (DTM): Within Guided Functions, select "Output diagnostic test mode (DTM)" and click "Perform."
5. Run Defogger Output Test: In the DTM test plan, locate the rear window defogger function and activate it. Allow this test to run for at least 30 seconds.
6. Recheck Function: After the output test completes, recheck the function of the rear window defog button.
7. Clear DTCs: Crucially, after performing the output test, clear any DTCs that were generated in the J393 comfort system central control module before proceeding with any other diagnostics.

Required Tools or Parts

The primary tool required for this procedure is the ODIS diagnostic system, which technicians use to perform the guided functions and output tests.

Important Warnings for Owners

• If your vehicle is outside of its warranty period, this Technical Service Bulletin is for informational purposes only, and any repair costs may not be covered.
• If the rear window defog button continues to fail after this procedure, further diagnostics outside the scope of this TSB will be necessary.
• Performing the output test will create DTCs in the comfort system central control module, J393 (address word 0046). Technicians must clear these DTCs before any further diagnostic work.

Owner Action

If you are experiencing an Audi e-tron rear defogger non-operational issue or similar problems with your 2021 Audi's rear defogger, it is recommended to visit an authorized Audi dealership. They can perform the diagnostic and repair procedure outlined in Technical Service Bulletin 2058452/2. This service is typically covered under warranty for eligible vehicles (up to 48 months/50,000 miles or for CPO Covered Vehicles).

Revision History

This Technical Service Bulletin, 57 21 74 2058452/2, was published on February 26, 2021. It supersedes Technical Service Bulletin Group 57 number 20-65, dated February 12, 2020. The revision included an updated header, model year information, and applicable vehicles.

Warranty Information

Warranty claims for this procedure fall under Claim Type 110 (up to 48 Months/50,000 Miles) or G10 for CPO Covered Vehicles. The Service Number is 5789, and the Damage Code is 0039. Diagnostic time is GFF 0150 0000 (maximum 60 TU). Road tests before and after the procedure have no allowance (0 TU).

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Source: NHTSA ID: 10187973