2002 grand prix getting poor gas mileage?

Answer 1

There are many reasons that your GP could be getting poor gas mileage. You have to start with regular maintenance items and go from there: 1. What condition is your Air Filter in?(It should be clean enough to see light through it) 2. Have you used fuel injector cleaner or had your injectors cleaned by someone? 3. How old are your spark plugs? (If you don't know--replace them) 4. Do your tires have proper inflation? (they can be low but look fine) These are some of the primary things you need to take care of. If all of these are taken care of then you may have bad Oxygen sensors. They degrade over time but still reduce emissions enough and work well enough to pass emissions tests and NOT light the SES light. But they DO cause bad gas mileage even when you don't get any other symptoms. I've had O2 sensors go bad at 40k miles. The only real way to tell if that is the problem is replace them. The dealer and most mechanics can't or won't tell you they are causing the problem.