Honda Civic
U0121
The U0121 code indicates a communication issue between the Engine Control Module (ECM) and the Transmission Control Module (TCM) on your 10th Generation Honda Civic (2016-2021).
3 SolutionsU-CodeNetwork
U
Error Code Type
Network
Components
2 affected
ElectricalBrakes
Symptoms
10 common
- •Check engine light illuminated
- •Transmission shifting issues or erratic behavior
- •Loss of power or acceleration
- +7 more
Most Affected Generations
1 generation
FC/FK
3
Top Affected Components
2 components
Electrical
2
Brakes
1
Severity Levels
2 levels
high
2
critical
1
Quick Facts
3
Total Solutions
2
Affected Components
10
Common Symptoms
1
Generations
All Solutions
Showing 3 of 3 solutions for error code U0121 across all generations.