How many oxygen sensors does the 2003 Toyota Corolla have?

There are 2 oxygen sensors on Your 2003 Toyota Corolla; one's upstream of the catalytic converter and the other's downstream of it. Here are some symptoms to look out for to determine if it's bad: The check engine light comes on, there's a loss of fuel efficiency, You have black smoke from the exhaust, and You may smell a sulfuric smell from the exhauSTSmoke. You can purchase a compatible sensor from Autozone or other car parts stores for about $67; replacing isn't difficult, but if You choose to pay someone else to do it, look to spend about $80 to $100 for that convenience.