Do I need to change both upstream and downstream for my car?

Whether you need to change both upstream and downstream components for your car depends on the specific issue you're addressing. For example, if you're replacing an oxygen sensor, it’s common to change both upstream (before the catalytic converter) and downstream (after the catalytic converter) sensors if they are both faulty. However, if only one is malfunctioning, you may just need to replace that one. Always refer to your vehicle's service manual or consult a mechanic for tailored advice.