U0121 on Honda: How to Diagnose & Fix
Lost Communication with ABS Module
1 Honda model · 1 documented issue · $150-$2,000 repair
U0121 on Honda by model: symptoms, diagnosis and fix
Honda HR-V models across all years experience electrical system problems including parasitic battery drain, premature battery failure, and stability control module failures. Owners report dead batteries after 24-48 hours of sitting, with the vehicle not holding a charge. Common causes include faulty door lock actuators causing constant drain, infotainment system staying on, and failing stability control modules. Stability control module replacement can cost $1,500+.
Common Symptoms
- Battery dies after 1-2 days of sitting
- Battery won't hold charge
- Multiple electrical warning lights
- VSA (stability control) warning light
- Infotainment system won't shut off
- Random electrical glitches
How to Fix
Perform parasitic draw test to identify the circuit causing drain (normal is <50mA). Common culprits: door lock actuators (pull fuse #13 to test), infotainment system, or stability control module. Replace faulty component. If battery is weak (load test <12.4V), replace battery first before chasing gremlins. OEM Honda battery: $150-250. Stability control module: $1,500-2,000.
What you need to diagnose it
The fix here starts with a test, not a part — which repair you need depends on what the test finds.This issue involves U codes, which a basic engine-code reader cannot see.
UNI-T UT210E Low-Current DC Clamp Meter
1 mA resolution on the 2 A range — a 0.1 A meter reads a 50 mA drain as zero
$40–$70View
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Testing and isolating the fault is DIY work. Replacing or reprogramming a control module is not — most are VIN-programmed, so a new one does nothing until a shop codes it to your car. Check for an open recall or service bulletin before buying anything.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- DieHard Platinum 51R-AGM battery, 435 CCAOEMDieHard 51R-AGM
Replacement battery branch only after charging-system and battery testing confirms the battery is failed or cannot hold rated capacity Fitment/availability: BCI Group 51R application for 2016-2023 U.S. Honda HR-V 1.8L/2.0L; confirm fitme…
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipHRVForum DIY: Pull fuse #13 (power door locks) overnight - if battery stays charged, you have a bad door lock actuator causing the drain.
- WarningDon't just keep replacing the battery - find and fix the parasitic drain or you'll kill battery after battery.
- TipDisconnect the infotainment harness overnight (under dash) - if drain stops, the head unit is staying awake and needs replacement/reflash.
Sources for this issue (2)
U0121 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does U0121 mean on a Honda?
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 Honda it is documented across 1 model: HR-V.
What are the most common causes of U0121?
The most common causes of U0121 are: 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. The specific cause varies by vehicle.
How much does it cost to fix U0121 on a Honda?
Published repair estimates on Honda range from $150 to $2,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for U0121 on a different make?
View U0121 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.