U0121 on Genesis
Lost Communication with ABS Module
U0121 on Genesis vehicles indicates lost communication with abs module. Au7o has documented this code across 1 Genesis model — most commonly on G90. U0121 is a network communication code meaning a control module on the vehicle's data bus has lost communication with the ABS (anti-lock brake system) module. Modern cars share information over a CAN bus, and when other modules stop receiving expected messages from the ABS unit, this code sets. Because the ABS module also handles traction control and stability control on most vehicles, you may see multiple warning lights and lost features. It points to a communication or power problem with the ABS module rather than a worn brake part. Typical repair costs on Genesis range from $400 to $2,500, depending on the specific model and root cause.
Common Causes of U0121
- •Loss of power or ground to the ABS module
- •Blown fuse feeding the ABS controller
- •Damaged, corroded, or loose ABS module connector
- •Open, shorted, or chafed CAN bus wiring
- •Internal failure of the ABS control module
- •Corrosion or water intrusion in connectors/harness
- •Faulty gateway module disrupting bus communication
U0121 on Genesis by Model
Genesis G90(1 issue)
- Intermittent dashboard warning cascade with electronic parking brake lockout2023
Multiple 2023 G90 owners report sudden 'dashboard lit up like a Christmas tree' events: every warning light illuminates, a 'STOP ENGINE / check brake system' message appears, and the electronic parking brake refuses to release, stranding the vehicle. One documented dealer diagnosis was a shorted main sensor, but the fault is intermittent and recurred one week after repair. Separate 2023 G90 electrical complaints (dead battery, door handles not deploying) suggest a broader pattern of low-voltage / sensor faults on the new RS4 generation.
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View U0121 across all makes →Frequently Asked Questions
What does U0121 mean on Genesis?▼
U0121 stands for "Lost Communication with ABS Module." U0121 is a network communication code meaning a control module on the vehicle's data bus has lost communication with the ABS (anti-lock brake system) module. Modern cars share information over a CAN bus, and when other modules stop receiving expected messages from the ABS unit, this code sets. Because the ABS module also handles traction control and stability control on most vehicles, you may see multiple warning lights and lost features. It points to a communication or power problem with the ABS module rather than a worn brake part. On Genesis specifically, this code is documented across 1 model.
What causes U0121 on Genesis vehicles?▼
Common causes on Genesis: Loss of power or ground to the ABS module, Blown fuse feeding the ABS controller, Damaged, corroded, or loose ABS module connector, Open, shorted, or chafed CAN bus wiring, Internal failure of the ABS control module. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix U0121 on a Genesis?▼
Repair costs on Genesis range from $400 to $2,500, depending on the specific model and root cause.
Which Genesis models have U0121 documented?▼
Au7o has documented U0121 on 1 Genesis model: G90.