Industrial O2OxygenSensorUpstreamDownstream Oxygen Sensor Set

The O2 Oxygen Sensor Upstream & Downstream Set for the 1999 Audi A6 and A6 Quattro 2.8L includes four heated oxygen sensors—two upstream and two downstream—to monitor exhaust oxygen content and catalytic converter efficiency as part of the engine management system. Designed as a direct-fit, OEM-style replacement, the set uses stainless steel housings and zirconia ceramic sensing elements, with a thread size of M18 × 1.5 and 12 V heaters, plus OEM-style plug-in connectors for installation at the exhaust manifold (upstream) and exhaust pipe (downstream). Compatibility covers 1999 Audi A6 and A6 Quattro equipped with the 2.8L V6 (30-valve) engine, with engine codes AFC, AHA, or ATQ depending on production date. Common replacements include Bosch 15733, Denso 234-4668, and Audi OEM Oxygen Sensor.