Most modern vehicles are equipped with an anti-lock braking system (ABS). The system prevents the wheels from locking up during emergency braking situations and whenever the roads are slippery. It also reduces the risk of skidding during a panic stop, which helps the driver maintain vehicle control.
The ABS has a control module that relies on the input from the wheel speed sensors to monitor the wheels’ deceleration rates during braking. This module also communicates with other on-board computers over the controller area network (CAN) bus to operate the entire ABS.
If the module is unable to receive and transmit information over the CAN bus, fault code U0121 will be logged by on-board diagnostics.
Fault code U0121 stands for “Lost Communication With Anti-Lock Braking System (ABS) Module.”
The ABS module issues the necessary commands to modulate brake pressure and maintain the correct percentage of tire slip under emergency braking and adverse road surface conditions.
If the module detects that wheel lockup is about to take place, it will command the hydraulic modulator to regulate fluid pressure accordingly. The prompt applies until the hydraulic control reaches its final phase, which is referred to as the pressure increase phase. This means that the maximum master cylinder pressure has been applied to the wheels.
Note: The definition of code U0121 might be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.
U0121 is a generic powertrain code that can be logged in vehicles with on-board diagnostics (OBD). Although this fault code is common, its steps for diagnosis and repair can vary from one vehicle to another.
If you’re not familiar with the process of diagnosing trouble codes yet, it’s best to have your vehicle checked by a certified mechanic. Otherwise, you can go ahead and do the job yourself.
Check out the video below to get an idea of what the process might involve.
Without the right tools and know-how, attempting to fix a U0121 code can be difficult. It can even lead to further complications if done incorrectly. So if you’re not confident with your DIY skills yet, it’s a good idea to bring your vehicle to the nearest repair shop and have a certified professional do the repairs for you.
But if you think you can do it, make sure you have everything you need before proceeding. It’s also a good idea to check out vehicle-specific repair information like those from Chilton or an ALLDATA subscription before you start.
Once you confirm that a faulty ABS control module triggered the U0121 code in your vehicle, it’s best to replace the part immediately. If you continue driving without replacing the control module, your vehicle might be more vulnerable to skidding on slippery roads because the ABS might not work. For a quality replacement ABS control module that fits your car and budget, look no further than CarParts.com.
At CarParts.com, you will surely find a part or accessory that will fit your vehicle. Simply select the year, make, model, and engine of your car or truck on our website’s vehicle selector to pull up the appropriate products from our catalog. Our parts are ready to ship from one of our distribution centers located across the US. If you live in the continental U.S. and order by 12 p.m. EST, you can expect to receive your new ABS control module in a few working days.
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Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.