I am writing to report a serious and ongoing safety issue with my 2021 Hyundai Elantra Hybrid that remains unresolved despite multiple visits to Hyundai service centers and independent repair shops. I’ve also found numerous consumer discussions online describing nearly identical issues with the same model and newer Elantra Hybrid models, suggesting this may be part of a wider systemic defect. The core issue lies within the vehicle’s hybrid system. Shortly after a recent system/software update performed at a Hyundai dealership, a warning message began appearing at random intervals stating: “Check Hybrid System.” This typically first appears after extended driving — often around 3 hours — but once it occurs, the issue worsens if I continue to drive. Each time the warning appears, the vehicle suddenly and drastically decelerates without driver input, becoming dangerously slow and unresponsive, even while traveling at highway speeds. This creates an urgent safety risk, as I have had to maneuver off the road quickly to avoid collisions. After the initial warning, if I attempt to drive the vehicle again without sufficient downtime, the warning reappears much more frequently — sometimes within minutes. The only temporary relief is to stop using the vehicle and allow it to rest for at least six hours, after which the issue may temporarily subside. In every case, I must use the 12V battery reset button to restart the car, which I suspect may be clearing diagnostic codes before they can be properly recorded. Notably, the check engine light disappears after this reset, even if it was previously displayed. Given that the hybrid battery is located beneath the rear passenger seat, I am deeply concerned that if there is an underlying thermal or electrical issue, it could pose a serious or life-threatening risk to passengers. To date, no dealership or technician has been able to duplicate or permanently resolve the problem.

Source: NHTSA complaint ODI #11661670 · view all complaints for this vehicle at nhtsa.gov

The contact owns a 2021 Hyundai Elantra Hybrid. The contact stated that while driving 60 MPH during ice and snow, the engine revved, and there was an abnormal sound coming from the Hybrid battery. While turning, the contact stated that the vehicle had unintendedly accelerated. Additionally, the tire pressure warning light was illuminated. The contact believed that the failure was related to the Hybrid battery. The vehicle was driven to the residence, where it remained parked and was not driven since. The manufacturer was notified of the failure. The failure mileage was 44,900.

Source: NHTSA complaint ODI #11708400 · view all complaints for this vehicle at nhtsa.gov

At around 93k miles my HECU unit apparently malfunctioned at the same time as the left front tire speed indicator. All of my safety features ABS, adaptive cruise control, lane departure, lane keeping etc do not work because of this.

Source: NHTSA complaint ODI #11621727 · view all complaints for this vehicle at nhtsa.gov

I was driving on the Highway at the posted speed limit when the warning "Check Forward Safety System" came up and remained on my dashboard. The cruise control stopped working also. The light remained on even after stopping and starting the car and has remained on ever since. I have never been in an accident nor has my computer system reported any collision. My Hyundai Blue Link app gives me the following DTC: C162078. It started on [XXX]. My collision detection system does not appear to be working at all and my cruise control no longer works. I'm very concerned about it malfunctioning based on other entries on the nhtsa.gov website. I took the car to Hyundai Service Center and they are trying to convince me this is due to a collision and warranty will not be covering it. They tried to charge me for diagnostic even though I already had the error code on the Hyundai BlueLink App. They confirmed that my computer has zero reports of any collisions. The service tech said, and I'm quoting, "The system is very sensitive and a swift kick could cause it to malfunction." That sounds like a manufacturing defect to me. I have never been in an accident with this car, there is zero visible damage to the front bumper, and my computer has no report of an accident. The dealership urged me to contact insurance. My Major Insurance Company told me this was absurd, would never be approved, and is clearly mechanical. They also mentioned anecdotally that this problem has been coming up a lot for them with modern Hyundai models. Then I called Hyundai Corporate and they have escalated the issue, agree it sounds mechanical, and will be contacting me in 3-5 business days. They apologized profusely so I am still holding out hope for warranty coverage. I believe the dealership is trying to blame me for this mechanical failure to avoid expense on their end. I have had many software-related issues with this car. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Source: NHTSA complaint ODI #11572957 · view all complaints for this vehicle at nhtsa.gov