WARNING: This page is about a different car, the 2019 Toyota Highlander, 2018 Toyota Highlander, and 2017 Toyota Highlander. However, it is still accessible from the selected car via links, so may be relevant.
INSPECT OIL COOLER ASSEMBLY
Visually check the oil cooler assembly for cracks or damage.
If cracks or damage are found, replace the oil cooler assembly.