What is the U0121 fault number? What is the description for the Anti-Lock Braking System’s (ABS) lost communication with the Control Module? How do you fix the U0121 fault code What are the causes and symptoms of U0121 fault code?
What is U0121? What is Fault Code? What does it mean?
U0121 is a general fault code for vehicle communication systems that can be applied to all makes and models. This code refers to the communication circuit between anti-lock brake system (ABS), control module, and other control modules. This communication circuit is also known as the controller area bus (CAN) bus.
Modern cars are equipped with anti-lock brake systems (ABS). ABS prevents locking of vehicles by modulating the brake pressure applied on the wheels in emergency situations and adverse road surfaces. The driver is also protected from skidding by ABS, which reduces the possibility of losing control.
ABS includes a control module that monitors data sent by the wheel speed sensors. This module monitors the wheel deceleration rate during braking. The controller area network bus (CAN) allows the module to communicate with other onboard computers and operate the entire system.
There are many vehicles that can be affected by the U0121 fault code, including, but not limited, to Mazda, Ford and Mitsubishi models.
What is the U0121 Fault Code?
Here are some reasons to set fault code U0121:
- – The wires are damaged, melted, broken, or corroded, which can cause an open or brief circuit in the CAN bus
- – Poor electricity due to open or short circuit problems in wiring to ABS control module.
- – Broken or bent pins in ABS control module sockets
- – Blown fuse
- – Dead battery or weak battery
- Communication could be lost if an unrelated control module has been replaced.
- – Defective ABS control module
Note: Some vehicles, especially Mazda models, may have this code set. If a diagnostic device is connected to the system, the malfunction lights might come on. The code’s presence is temporary and does not necessarily indicate a malfunction. Usually, the problem is resolved by clearing the code.
What are the symptoms for U0121 fault code?
You may experience the following symptoms if you own a vehicle that has the code U0121:
- – Illumination at the check engine lights
- – ABS, Traction and Stability Control Misfunction Lights on (TRAC/ESP/ESC lights might come on depending upon manufacturer and vehicle equipment).
- ABS system is not working
- – Stability control and traction systems may not be functional
- – Sometimes the engine might not start.
- You can limit the vehicle’s speed by activating the failsafe mode
- – Setting related fault codes
How to Fix the U0121 Fault Code
The following repairs can help resolve the U0121 fault code
- – Repair or replacement for damaged, melted and corroded wires that are causing an open or brief circuit on the CAN bus
- Repair or replacement of short or open circuiting wires that are melted, corroded or damaged to the ABS control module
- – Replacing blownfuses
- – Clean the ABS control module connectors that are corroded
- – Repair bent or broken pins
- – Replacing the defective ABS module
- – Testing the battery and, if necessary replacing it
How serious is the U0121 Fault code?
Failures in control modules must always be considered seriously. This code will most likely cause the ABS system to stop working properly. This code must be corrected as soon as possible as malfunctioning safety systems or brake system will increase accident risks.
