Learn more about the Audi U0121 code.
U0121 OBD-II Trouble Code
Understand what U0121 means for your Audi and book diagnostics with our VAG specialists.
What is Code U0121?
When your Audi’s check engine light turns on and shows this code, it means the On-Board Diagnostic (OBD-II) system has detected an issue with A dead battery, A faulty ABS module, A problem with ABS module circuit, A problem with the CAN bus.
In plain terms, the system that controls your engine timing may not be adjusting correctly, affecting performance and efficiency.
U0121
A dead battery, A faulty ABS module, A problem with ABS module circuit, A problem with the CAN bus.
U0121 – Technical Description
- Audi OBD-II Code: U0121
- Fault Type: A dead battery
How We Diagnose Audi Fault Code U0121
At VGS Performance, we use dealer-level Audi diagnostic tools to confirm the root cause before any repair work begins. Our diagnostic service includes:
Learn more about our diagnostic services.
FAQs About Code U0121
What does U0121 mean on an Audi?
It indicates a fault with A dead battery, A faulty ABS module, A problem with ABS module circuit, A problem with the CAN bus.
What does an Audi OBD-II code mean?
Every code points to a specific fault detected by your Audi’s onboard computer. So codes such as U0121helps our Swindon technicians locate issues faster and more accurately.
Can I clear OBD codes myself?
You can clear codes with a scanner, but if the issue hasn’t been properly fixed, the fault will return. It’s best to bring your Audi in so we can diagnose and resolve it correctly.
How do I know if the U0121 code is a Audi-specific?
Codes starting with “P1”, such as U0121, are usually Audi or VAG-specific fault codes. These relate to systems and components unique to the Audi or wider VW Group range. Generic codes beginning with “P0” apply to most manufacturers and cover standard engine and emissions faults.
Audi Models Commonly Affected by Code U0121
The Audi U0121 fault code can appear across a range of models and engines within the Audi lineup. Because many vehicles share similar electronic and timing systems, this code isn’t limited to one particular model.
We’ve seen codes like U0121 appear on cars such as the Audi A3, A4, A5, Q5 and TT, as well as other petrol and diesel variants. In most cases, it’s the engine management system detecting a performance or communication issue that needs to be checked.
Whether you drive a compact Audi A3 or a larger Q-series SUV, our diagnostic equipment can read and interpret the fault accurately. Once identified, we’ll confirm the cause and advise on the best next step to keep your Audi running as it should.
Although the fault details vary, the core issue usually relates to A dead battery, which requires accurate testing and data analysis. We use dealer-level VAG diagnostic tools to monitor live data, verify system performance, and pinpoint the exact cause before carrying out any repairs.
Need Help with Code U0121?
If you’ve scanned your Audi and found U0121 If you’ve scanned your Audi and found P0010, our team can confirm the fault and carry out any repairs needed. We use official VAG equipment to ensure accuracy and reliability.
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