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What 49 owners told NHTSA about the 2021 Mazda Mazda3 Sedan

These are the actual owner complaints behind this car’s reliability verdict, filed with the federal government, unedited. They’re unverified reports, not confirmed defects: read them as leads for your pre-purchase inspection, not a diagnosis.

All (49)Crash / fire / injury (4)Engine (18)Driver assistance (7)Electrical system (6)Airbags (4)Brakes (4)Lane Departure (3)Transmission & drivetrain (3)Body & structure (2)Fuel system (2)Speed control (2)

3 of 49 complaints match · Transmission & drivetrain · clear filters

Jan 25, 2026Transmission & drivetrain

My rear differential case cracked, anytime the four wheel drive system was engaged the entire drivetrain would lock up. Luckily we were only on side roads so going less than 30 mph if we had been on the highway when this happened we could have been in an accident or lost control. The dealer did confirm the problem and it was fixed under an extended warranty. There was no warning just all of a sudden a loud bang and all the wheels locked up. I have a copy of the video inspection done at the dealer if there's anyway to send that. I can get a copy of the repair invoice if needed

NHTSA ODI 11713224

May 27, 2025Transmission & drivetrain

I was driving when all the sudden there was a loud bang sound. The differential housing cracked. The when awd is demanded the rear diff was was locking up instead of engaging. Luckily we were just on city streets and not on the highway as this rear wheel locking up could cause a crash. Mazda wasn't very helpful with the replacement. Luckily I had a aftermarket warranty but it only paid for a used replacement, which is also failing. I have read lots of stories of this rear differential failure across all types of Mazda's from this era and really wish they would do the correct thing and resolve the problem.

NHTSA ODI 11663288

Nov 26, 2024Transmission & drivetrain

Radiators are failing 3 years after the warranty period. Its leading to coolant lost and perhaps overheating the engine.

NHTSA ODI 11627559

Working with the data? Download all 49 complaints as CSV · fetched from NHTSA July 18, 2026

How to use these: a complaint is one owner’s report, filed voluntarily and published unverified. Patterns matter more than any single story. If several owners describe the same failure at similar mileage, put that system at the top of your pre-purchase inspection list. Back to the full 2021 Mazda Mazda3 Sedan verdict →