Thank you so much, ChrisS

That very helpful. I live in California, it doesn't show any sight of corrosion. It's throw a code when i went up hill. my car has almost 200K miles. I think it's time to replace.
i check on Amazon only around $20-40 each. Kragen auto part store wants $75, dealer want $200. I think i will go with Amazon.
But I don't know which part number is the correct one, anyone know? please, help. Very appreciated.
Ericspyder