The check engine light came on to replace an engine part. My family mechanic, whom we have trusted for years/generations, told me that he could clearly see sludge in my engine when he replaced this part. He said he has seen other Terrains with the same issue. He told me that it will run great for a while, until it doesn't. When it stops running great, I will have to pour money into it to keep it going. He advised me to trade my vehicle in as soon as I'm able.