2025-2026 Audi A5/S5/A6 Door Won't Open DTC B122D29

Symptoms

Owners of affected 2025-2026 Audi A5, S5, and A6 vehicles may experience a specific issue where one of the doors cannot be opened intermittently from the outside. While the exterior handle may not work, the door can always be opened from the inside. All other doors on the vehicle will function normally without issue. Interestingly, once the interior door handle of the problematic door has been pulled out, the door can then be opened again from the outside for a period.

Fault Codes / DTCs

During diagnosis, workshops may find that the Diagnostic Trouble Code (DTC) "B122D29 - Lock unit for central locking - implausible signal - passive/intermittent" is logged in the diagnostic address of the door control unit for the faulty door. This specific fault code indicates an implausible signal from the central locking unit, pointing to a potential issue with the door lock or its control.

Technical Background

Audi has identified the root cause of this door opening issue as a software and/or hardware problem within the door control unit or the door lock assembly itself. This underlying technical issue leads to the intermittent failure of the exterior door handle.

Diagnosis / Trigger Conditions

To accurately diagnose the Audi A6 door won't open B122D29 issue, technicians will first attempt to reproduce the customer's complaint. If the DTC B122D29 is logged, the next step involves a precise resistance measurement on the installed door lock. This measurement is performed between pin 2 and pin 4 of the door lock connector using a multimeter. Before taking the measurement, the door lock must be put into a temporary crash redundancy (TCR) mode. This mode is initiated by removing the connector from the lock and then firmly pulling the interior door handle twice.

Expected resistance values are crucial for diagnosis:

• Temporary crash redundancy (TCR) (without operating door handles): The expected value is 1000 ohms. A measured value of 1000 ohms confirms the lock is in TCR mode, meaning it can only be opened mechanically. If the value is not 1000 ohms, the interior door handle should be pulled twice again as far as the stop, and the measurement repeated.
• Switch for interior door handle (IDH) + TCR (operating interior door handle only): The expected value is 382 ohms. A measurement tolerance of +/- 1% applies in each case.

After these initial measurements, the door should be closed, opened again, and the measurement repeated. At this point, if the TCR measurement now shows an open load (OL) instead of 1000 ohms, this is considered the expected result. Figure 1 in the TSB illustrates the connector for both the right and left door locks, guiding technicians on the correct measurement points.

If the complaint occurs without DTC B122D29 being logged, technicians should verify that the complaint can be reproduced. They must then check if the issue also happens when the vehicle is unlocked. This helps determine the root cause and the appropriate repair path.

Repair Procedure Summary

The repair procedure for the Audi A6 door won't open B122D29 issue is contingent on the diagnostic findings:

With DTC B122D29 Logged

1. Resistance Measurement: Perform the resistance measurements as described in the diagnosis section. If the measured values deviate from the specified 1000 ohms or 382 ohms, the affected door lock should be replaced.
2. Wiring Check & Control Unit Replacement: If the resistance values correspond to the expected specifications, the lock wiring should be checked according to Guided Fault Finding instructions. If the wiring is confirmed to be okay, then the door control unit for the faulty door should be replaced.

Without DTC B122D29 Logged

1. Reproduce Complaint: Verify that the complaint can be reproduced by the technician.
2. Unlocked Vehicle Check: Determine if the issue occurs when the vehicle is unlocked.
   • If Yes: If the door cannot be opened from the outside even when the vehicle is unlocked, the door control unit on the faulty door should be replaced.
   • If No: If the issue does not occur when the vehicle is unlocked, the repair should be postponed. In this scenario, the TSB states, "The complaint cannot be reproduced" under specific conditions. Replacing parts or attempting repairs will not resolve the problem.

Software Update Consideration

If the complaint cannot be reproduced, technicians should check whether Technical Service Bulletin 2079690, titled "00 Combined software update 03.10.00/C (28.13.01) KD2," is applicable and visible for the vehicle. If this TSB is applicable, the software update described within TSB 2079690 should be performed to address the issue.

Required Tools or Parts

For the diagnostic procedure, a multimeter is required to measure the resistance of the door lock. Specific part numbers for replacement door locks or door control units are not detailed in this TSB but would be determined based on the diagnostic outcome and vehicle specifications.

Important Warnings

Owners and technicians should be aware of a critical warning from Audi regarding this issue: if the complaint cannot be reproduced, replacing parts or attempting repairs will not fix the problem. Audi explicitly states that "Unjustified work/replacement parts will be charged back. Invoicing under warranty is not permitted" in such cases. This emphasizes the importance of thorough and accurate diagnosis before proceeding with any part replacements or extensive repairs.

Warranty Information

Warranty claims related to Technical Service Bulletin 2079919/1 must strictly adhere to the Audi Warranty Policies and Procedures Manual. If the vehicle is outside of any warranty coverage, this Technical Service Bulletin is for informational purposes only.

Key service numbers and labor operations for claiming this repair include:

• Service Number 6438: For problems reproduced without DTC "B122D29 - Lock unit for central locking - implausible signal."
• Service Number 5717: For front lock measure/replace procedures.
• Service Number 5817: For rear lock measure/replace procedures.

The damage code for this issue is 0040.

Specific labor operations and their time units (TU) are detailed based on the diagnostic outcome and part version:

• Remove and install front door trim: Labor operation 7059 1900.
• Remove and install rear door trim: Labor operation 7073 1900.
• With DTC B122D29 AND part is 08S or higher AND issue reproduced with door locked/unlocked: Check door locks (5717 0299 or 5817 0299), 10 TU.
• Without DTC B122D29 AND part is 08S or higher AND issue not reproduced: Check door locks (5717 0299 or 5817 0299), 10 TU.
• For software update according to TSB 2079690:
  • Software Update, including connecting battery charger (0151 0010).
  • Fixed rate for software update, including all required preliminary and follow-up work (0151 0040), 130 TU.
• With DTC B122D29 AND measure NOK AND part is 07S or lower: Measure door locks (5717 0499 or 5817 0499), 20 TU.
• Remove and install door lock: Labor operations 5717 1950 or 5817 1950.
• With DTC B122D29 AND measure OK AND part is 07S or lower OR without DTC B122D29 AND part is 08S or higher AND issue only reproduced with door unlocked: Measure door locks (5717 0499 or 5817 0499), 20 TU.
• Remove and install door control unit: Labor operation 6438 1950.
• After any of the above repair actions are taken: GFF / Guided Functions (0150 0060).

The claim comment for this TSB is "As per TSB 2079919/1." It's also noted that when performing the combined software update, time stamps are not required for billing under warranty, allowing work on other vehicles simultaneously or by non-productive personnel.

Owner Action

If your 2025-2026 Audi A5, S5, or A6 is experiencing an intermittent door opening issue from the outside, especially if you suspect an Audi A6 door won't open B122D29 fault, it is recommended to schedule an appointment with an authorized Audi service center. Provide them with a clear description of the symptoms and mention Technical Service Bulletin 2079919/1. The dealership will perform the necessary diagnostic steps to identify the root cause and apply the appropriate repair or software update. Be prepared to explain the conditions under which the fault occurs, including whether it happens when the vehicle is unlocked.

---

Source: NHTSA ID: 11026250