2022 Audi A3/S3/RS3 3rd Brake Light Warning DTC B12C615

Owners of certain 2022 Audi A3, S3, and RS3 models may encounter an instrument cluster warning message related to the vehicle's 3rd brake light. This issue, identified by Audi Technical Service Bulletin (TSB) 2067742/1, specifically addresses situations where a warning is displayed, but the high-mount brake light itself continues to operate normally. The underlying cause has been traced to diagnostic software that is overly sensitive, leading to false alerts. If you are experiencing an Audi S3 3rd brake light B12C615 warning, this TSB provides crucial information.

Symptoms

If you own a 2022 Audi A3, S3, or RS3, you might observe the following symptom:

• "A warning for the 3rd brake light is displayed in the instrument cluster however the lamp continues to work normally."

Technicians have noted that this warning typically disappears after the ignition is cycled (switched off and then on again). Furthermore, inspections confirm that the wiring for the 3rd brake light is intact and the light functions as expected, despite the warning message. This indicates that the warning is often a false positive rather than a genuine component failure, and the 3rd brake light itself is fully operational.

Fault Codes / DTCs

When this condition occurs, the following Diagnostic Trouble Code (DTC) is stored in the Electronic Central Electrical (BCM), specifically in control module J519 (address word 0009):

Code	Description
B12C615	Bulb for high-mount brake light open circuit/short circuit to B+_intermittent

This DTC, B12C615, points to an intermittent open circuit or short circuit to battery positive in the high-mount brake light bulb circuit. However, as the TSB clarifies, this is a misinterpretation by the diagnostic system.

Diagnosis and Technical Background

The root cause of the false warning and the stored DTC B12C615 is attributed to overly sensitive diagnostic software within the Electronic Central Electrical (BCM), module J519. This software incorrectly detects an intermittent open circuit or short circuit in the 3rd brake light system, even when all components are functioning correctly. Workshop findings consistently show that the 3rd brake light wiring is intact, the lamp operates normally, and the warning often clears after the ignition is turned off and on again. This confirms that the issue is a software misinterpretation rather than a physical defect.

Important Warnings for Owners and Technicians

Audi has issued specific instructions regarding this condition to prevent unnecessary repairs:

• "Do not replace any components for this condition since this will not resolve the customer's concern." This explicitly means that replacing the 3rd brake light bulb, the entire light assembly, or any related wiring will not fix the underlying software sensitivity issue.
• "There is no need to remove/replace suppression capacitor C24 in the wiring harness for the 3rd brake light." This component is not the cause of the false warning.
• This Technical Service Bulletin (TSB 2067742/1) does not apply if the 3rd brake light is genuinely inoperative and connection issues have been ruled out. In such cases, normal diagnostic procedures for a faulty brake light should be followed.

Manufacturer's Response and Pending Solution

Audi is actively working on a resolution for this issue. A software solution is currently being prepared and is expected to become available by the end of the first quarter of 2023. This timeline is subject to change. Until the software update is released, technicians are advised to explain the situation to customers and create a PSS (Pending Service Solutions) record in the PSS application via AccessAudi or the Technical Assistance page in Elsa. This allows Audi to track instances of the Audi S3 3rd brake light B12C615 issue and ensure customers are informed about the upcoming fix.

Warranty Information

This Technical Service Bulletin (TSB 2067742/1) is provided for informational purposes only. It is not applicable for direct warranty claims. Any part and service references within this TSB are subject to change. Technicians should always consult the latest information from their Parts Department, ETKA, and the Repair Manual for current details on fasteners, bolts, nuts, and screws that may require replacement during any repair.

Source

NHTSA ID: 10224673