2021 Hyundai Sonata engine problems

“At approximately 130,000 miles, vehicle developed and internal coolant leak caused by a failed Exhaust Heat Recovery System (EHRS) in the center muffler assembly, matching TSB 23-EM-009H - a known manufacturing defect documented by Hyundai. Coolant has been slowly leaking internally into the exhaust system. The authorized Hyundai dealership initially failed to diagnose the internal leak and told me there was no leak and wanted to send me home. After pushing back, the internal leak was confirmed. If not caught, this defect could result in engine overheating or complete engine failure without warning. Hyundai Motor America has denied goodwill coverage despite this being a documented manufacturing defect.”

“The car will idle high around 1200 rpms. The car will most of the times fix the issue when you turn the car off and back on but it will start again after driving. This is a known issue with the car. I have had the egr valve replaced since it will pop up the codes P240F and P049 for egr slow response and control position exceeded learning limit but the problem came back within two days. I did find a forum that deals with the joint connector repair but this needs to be a recall as I have come across many people who have this problem and paying out of pocket to fix it.”

“The contact owns a 2021 Hyundai Sonata. The contact stated while driving at an undisclosed speed, the engine shuddered and the engine stalled. In addition, the engine seized. No warning lights were illuminated. The contact stated that the vehicle was seized in the middle of the road. The contact stated that while attempting to start the vehicle, the vehicle started. The failure reoccurred. The vehicle was towed to the residence. The vehicle was not diagnosed or repaired by an independent mechanic or dealer. The manufacturer was made aware of the failure. The failure mileage was approximately 140,000.”

“The Exhaust Heat Recovery System (EHRS) has failed for the second time on this vehicle. The first failure occurred at approximately 35,000 miles and was repaired under Hyundai Technical Service Bulletin 23-EM-009H, which Hyundai issued to address this exact defect across 2020-2023 Sonata Hybrid models. The vehicle has now reached 71,000 miles and is experiencing the identical symptoms: coolant loss, overheating, and white exhaust smoke. The EHRS shares a coolant loop with the hybrid battery thermal management system. Coolant loss from this failure puts the hybrid battery and power electronics at risk of overheating, creating a potential fire and safety hazard. The recurring nature of this failure following an official TSB repair suggests the root cause has not been adequately addressed by Hyundai's current repair protocol.”

“The internal core of the Exhaust Heat Recovery System (EHRS), part of the center muffler/front pipe assembly (#28600-L5210), suffered a catastrophic failure. This allowed approximately 9 gallons of engine coolant to leak directly into the hot exhaust stream. Safety Risk: This failure creates a severe visibility hazard. During acceleration from stop lights and stop signs, the vehicle emits massive, thick clouds of white glycol smoke. The smoke is so dense that it completely obscures the driver's view of trailing vehicles and prevents following drivers from seeing the roadway or my vehicle's brake lights, creating a high risk of rear-end collisions. Additionally, the rapid loss of coolant caused the engine to overheat and lose power while in motion, nearly causing a stall in active traffic. Confirmation: The failure was confirmed by the service department at Washington Hyundai (Invoice #174281). This is the second failure of this specific component (previously failed in Jan 2025). The manufacturer issued TSB 23-EM-009H for this defect, acknowledging it affects 2020-2023 Sonata Hybrids, but no safety recall has been issued. Symptoms: The issue was preceded by a…”

“Hyundai technical service bulletin 23-EM-009H (EHRS COOLANT LEAK) - AKA a faulty heat exchange that causes the coolant to leak into the exhaust and burn away. Resulting in a very hard to diagnose coolant disappearance. This should be a recall. They have literally already acknowledged a manufacturer defect with the service bulletin. The problem is that in most cases, it occurs out of the 60k or 100k warranty. The dealer seems to have discretion as to which of the mileage limits apply. One dealer in NC told me 60k and my local in SC told me 100k. My problem started at 90k, but was just topped off on fluid and repaired as "normal evaporation". Now 12k later at 102k, they acknowledged the TSB but claimed I was out of warranty. With me being out of warranty, they claimed that Hyundai would not send them tsb parts and that I would need to replace the whole system with the normal skus around 3k.”