Why should you change an oxygen sensor? It is critical that oxygen sensors are replaced at the How to diagnose suggested intervals provided by vehicle manufacturers before the sensor fails. Following the State of oxygen sensor: recommendations will prevent long term damage to a Greenish, grainy discoloration. Possible cause: vehicle’s engine, reduce harmful carbon dioxide (CO2) Antifreeze has escaped and entered the combustion chamber. emissions and save money when refueling your vehicle. Measure: Replace the oxygen sensor. Check the engine block, cylinder head, intake An oxygen sensor’s service life varies: oxygen sensors manifold and head gasket for wear and cracks. with 1 – 2 wires have a typical service life between 30,000 – 50,000 miles; while 3 – 5 wire sensors have a life span of up to 100,000 miles. Checking and State of oxygen sensor: Blackened, with oily contamination. replacing worn out oxygen sensors has become a Possible cause: critical part of regular vehicle maintenance. Excessive oil consumption. Measure: Check the valve guides and seals, which may be worn. Replace the A worn out oxygen sensor can cause oxygen sensor. f Engine performance issues f Lower miles per gallon fuel efficiency State of oxygen sensor: Dark brown discoloration. f Excessive harmful exhaust emissions Possible cause: Air-fuel mixture too rich. Measure: f Catalytic converter damage Check the fuel pressure. Replace the oxygen sensor. Replacing a worn oxygen sensor f Improves engine performance f Reduces harmful emissions State of oxygen sensor: Reddish or white discoloration. Possible cause: f Optimizes fuel delivery for maximum Fuel additives in the gasoline. miles per gallon Measure: Do not use fuel additives. Replace the oxygen sensor. f Prevents catalytic converter failure Oxygen sensors are important engine components – State of oxygen sensor: Broken cable. indispensable for reliable Possible cause: engine function and correct Excessive cable tension. emission values. But the Measure: Replace the oxygen sensor. perfect functioning of oxygen Route the new cable without tension. sensors can be jeopardized by many factors: f Environmental influences, such as salt and dirt State of oxygen sensor: The molded cable tubing is damaged. f Large temperature fluctuations Possible cause: Impact by stone chippings. f Poor-quality fuel Measure: Replace the oxygen sensor. f Soot and oil residues in the exhaust gas ©2014 Robert Bosch LLC, USA. All rights reserved. BOSCH is a registered trademark of Robert Bosch GmbH and/or its affiliated entities. 14060253 V3.