Hyundai and Kia vehicles equipped with Theta II engines (GDI) were recalled, due to the fact that those engines were, and continue to be, the subject of an investigation by the National Highway Traffic Safety Administration (NHTSA). Safety regulators are investigating if Hyundai and Kia did enough in a timely manner with regards to the recalls of nearly 1.7 million vehicles with Theta engines, which were prone to an abnormal amount of noise and seizing.

In September 2015, Hyundai recalled about 470,000 model year 2011-2012 Sonatas equipped with 2-liter and 2.4-liter Theta II engines. At the time, Hyundai told NHTSA that manufacturing problems left metallic debris around the engine crankshaft, causing problems with oil flow. The pieces of metal interfere with the oil flow through the connecting rod bearings and damage the connecting rods. The automaker blamed the problem on a mechanical "deburring" process used to remove metallic machining debris from the crankshaft.

By April 2017, Hyundai expanded the 2015 recall by including another 572,000 vehicles with Theta II engines, including 2013-2014 Hyundai Sonata and Santa Fe Sport vehicles. Hyundai told safety regulators the same metal debris problem caused the expanded recall. Near that same time, Kia told NHTSA about a recall of more than 618,000 model year 2011-2014 Kia Optima, 2012-2014 Sorento and 2011-2013 Sportage vehicles because the Theta engine bearings wore out too early and caused the engines to seize. Kia said it didn't recall the vehicles in 2015 when Hyundai first recalled its cars because the Theta II engines in the Kia vehicles were built on a different production line and had different problems than Hyundai. In addition to customers complaining about the Theta II engines, a Korean whistleblower who worked for Hyundai as an engineer let NHTSA know what he knew.

Also in April 2017, Hyundai and Kia Motors planned to recall 170,000 vehicles in South Korea from five models, including their Grandeur and Sonata, after acknowledging a defect in the Theta 2 engines used in them. Eventually, 520,000 vehicles were recalled in South Korea.

Owners started suing after the automaker refused to pay the thousands of dollars to repair or replace the engines, with one lawsuit from 2015 alleging a dealer wanted $4,500 to do the work. Kia was also served papers over a class-action lawsuit in 2016 filed by owners of vehicles equipped with Theta engines. NHTSA says it took action to "investigate both the timeliness and scope of Hyundai's Theta II engine recalls, and Hyundai's compliance with reporting requirements."

In Canada in 2019 Hyundai announced a recall for most vehicles using the affected engines, however a class action lawsuit was filed in 2018 as a result of failures of this engine used in Canadian Forte models and lack of manufacturer support against Kia Canada Inc.

On December 1, 2020, Hyundai and Kia recalled 423,000 vehicles equipped with various engines following a joint review by Hyundai and the NHTSA, of which the 2.4L Theta II MPI engines were a part of. This marks the first instance of the MPI variants of these engines being recalled. Affected vehicles include the 2011-2013 Hyundai Sonata Hybrid, 2012 Hyundai Santa Fe, 2012-2013 Kia Sorento, 2011-2013 Kia Optima Hybrid, 2012-2013 Kia Forte and Forte Koup, and the 2012 Kia Sportage 2.4l.