Common signs include a check engine light (codes P0130-P0167), poor fuel economy, rough idle, failed emissions test, and sluggish acceleration. Most O2 sensors should be replaced every 60,000-90,000 miles for optimal performance.

Check your vehicle's fitment to confirm position. Upstream sensors (Bank 1/2 Sensor 1) are before the catalytic converter and control fuel mixture. Downstream sensors (Sensor 2) are after the converter and monitor catalyst efficiency.

Not necessarily, but sensors of similar age often fail around the same time. If one sensor fails, others may be nearing end of life. For optimal fuel economy and emissions, consider replacing sensors in pairs.