I just changed the oil in the 99 a couple of nights ago. Just this morning, my "service engine soon" light comes on. It's steady and not flashing. Gas cap is secure. The last oil change was with Penzoil SAE 5W-30 just like before when I had it done by someone else. Then a couple of nights ago I thought that I should start using the synthetic oil so I threw some Mobil 1 5W-30 Synthetic in there. I've heard rumors of not mixing oil but that's all bullshit. New oil especially synthetic can't be what's causing my light to come on. Any ideas guys?

 

I doubt its the oil causing the SES light but if you've switched to synthetic you probably need ot continue using synthetic

 

go to autozone and get the code pulled, tell us what they say.

Or check under thehood, for all wires, make sure none got bumped when you did the oil change (doubtful)

Ryan.

 

Not true at all . I just went back to dino oil for my last oil change. Doesn't make any difference.