This study examines potential assessment bias based on students' primary language status in PISA 2018. Specifically, multilingual (MLs) and nonmultilingual (non-MLs) students in the United States are compared with regard to their response time as well as scored responses across three cognitive domains (reading, mathematics, and science). Differential item functioning (DIF) analysis reveals that 7-14% of items exhibit DIF-related problems in scored responses between the two groups, aligning with PISA technical report results. While MLs generally spend more time on the test than non-MLs across cognitive levels, differential response time (DRT) functioning identifies significant time differences in 7-10% of items for students with similar cognitive levels. It was noticeable that items with DIF and DRT issues show limited overlap, suggesting diverse reasons for student struggles in the assessment. A deeper examination of item characteristics is recommended for test developers and teachers to gain a better understanding of these nuances.