U1121: Databus - Missing Message
10 vehicles · 1 makes
Most Reported On
U1121 is an OBD-II diagnostic trouble code meaning “Databus - Missing Message.” The control module expected a specific message on the data bus and it never arrived within the required time window. Like U1111 this is a downstream complaint - the module reporting it is fine, but a peer module or the bus itself stopped delivering data. Audi TSB 2061788 lists U112100 ("Databus missing message") among the codes stored in high-voltage battery charger J1050 on 2020-2021 e-tron, where the cause was outdated onboard-charger software; on SQ5/SQ8 air-suspension complaints (Audi TSB 2059363) it points at the air-suspension controller J1135 dropping off the bus. This code is most commonly reported on 2018-2025 Audi SQ5, 2020-2025 Audi SQ8, and 2019-2025 Audi A8 (Air-suspension-equipped), plus 7 other vehicles.
Common Causes
Diagnostic Tools
U1121 does not use the standard P/B/C/U prefix. It may be a manufacturer-specific code, so verify that a scanner supports your exact year, model and module before buying.
Vehicles Affected (10)
Air-Suspension Warning with C1260F0 or U112100 Communication Fault
2020-2025 SQ8 Air-Suspension J1135 Communication Fault - TSB 2059363/6
2019-2025 A8 Air-Suspension Warning C1260F0/U112100 - TSB 2059363/6
2019-2023 e-tron Air-Suspension Warning with J1135 Communication Fault - Diagnosis Required
2019-2025 Q8 Air-Suspension J1135 Communication Fault - TSB 2059363/6
2020-2024 S8 Air-Suspension Malfunction with J1135 Communication Fault - Diagnosis Required
2021 e-tron Charging Interruptions with Onboard-Charger Software 0070 - Diagnosis Required
2021-2025 RS7 Air-Suspension J1135 Communication Fault - TSB 2059363/6
2021-2024 RS6 Air-Suspension Warning - Check C1260F0 or U112100
2020-2025 RS Q8 Air-Suspension J1135 Communication Fault - TSB 2059363/6
2020-2025 SQ7 Air-Suspension C1260F0/U112100 Communication Fault - Diagnosis Required
FAQ
What does U1121 mean?
U1121 stands for "Databus - Missing Message." The control module expected a specific message on the data bus and it never arrived within the required time window. Like U1111 this is a downstream complaint - the module reporting it is fine, but a peer module or the bus itself stopped delivering data. Audi TSB 2061788 lists U112100 ("Databus missing message") among the codes stored in high-voltage battery charger J1050 on 2020-2021 e-tron, where the cause was outdated onboard-charger software; on SQ5/SQ8 air-suspension complaints (Audi TSB 2059363) it points at the air-suspension controller J1135 dropping off the bus.
What are the most common causes of U1121?
The most common causes of U1121 are: Transmitting control module offline, failed, unpowered, or not coded, Outdated module software producing spurious bus timeouts (documented on Audi e-tron OBC software 0070), CAN wiring damage, corroded connector, or poor ground, Gateway J533 installation list not matching the vehicle's actual modules, Low battery voltage or a discharged battery causing modules to drop off, Aftermarket electrical accessory loading or disturbing the bus. The specific cause varies by vehicle.
How much does it cost to fix U1121?
Repair costs vary widely depending on the root cause and vehicle.
Which vehicles are affected by U1121?
Au7o has documented U1121 across 10 vehicle models from 1 manufacturers: Audi.
Sources (4)
- TSBAudi TSB 2059363/6 - Air Suspension Warning with C1260F0 or U112100
- TSBAudi TSB 2059363/5 - Air-Suspension Warning with C1260F0 or U112100
- TSBAudi TSB 2059363/4 - Air Suspension Malfunction, J1135 Communication or Missing Message
- TSBAudi TSB 2061788/2 - Charging Problems with Onboard-Charger Software 0070
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.