O2 Oxygen Sensor Rear Downstream for Chevy GMC Pickup Truck (2002-2007)Stop burning more fuel than necessary in your big block or heavy duty hauler and finally clear that Check Engine Light with a direct fit sensor replacement. Replacement Oxygen Sensor for Chevy Silverado, GMC Sierra & Hummer H2 (6. 0L 8. 1L Vortec) If you are driving a heavy duty GM truck from the early 2000s, you know that the Vortec 6. 0L and the massive 8. 1L Big Block are legendary for their towing capacity, but they aren't exactly known for