Contaminated O2 Sensor

Tech Tip: A Day In The Life Of A Contaminated O2 Sensor

Since the oxygen sensor is in the exhaust stream, it can become contaminated over time. Much like a spark plug, the oxygen sensor can be examined and "read" to determine what the cause of contamination might be.

Since the oxygen sensor is in the exhaust stream, it can become contaminated over time. Much like a spark plug, the oxygen sensor can be examined and “read” to determine what the cause of contamination might be. 

• Black sooty deposits would indicate an excessively rich fuel mixture condition or oil blow-by in an older engine.

• A common type of contamination is due to coolant being burnt in the combustion chamber likely due to an engine gasket leak. See Fig. 3. figure 3: antifreeze contaminated o2 sensor

• Lead poisoning is no longer common, due to the lack of leaded fuel, but the emulsifying of the “terne” plating inside a steel fuel tank due to the excessive use of fuel system cleaners or alcohol can cause this same condition. 

Typical Switching Oxygen Sensor Diagnosis

• Look at the sensor voltage when the engine is cold and the ignition is first switched on. The heaters will cause the sensor to conduct current. Watch for the bias voltage to gradually lower as the sensor heats.

• Watch for the sensor to come down to less than 100 mV within three minutes of KOEO time. After three minutes, all sensors should have about the same voltage with the KOEO. A failed or contaminated sensor may be slow or may not get down to 100 mV at all.

• If one of the sensor voltages remains high, that sensor could be causing a no DTC ­driveability concern. 

Oxygen Sensor Replacement

• The primary sensor is on the manifold or the exhaust pipe; late-model vehicles also have sensors farther downstream. Because many late-model vehicles have multiple oxygen sensors, be sure you correctly identify the bad sensor so you do not mistakenly replace the wrong one.

Vehicle manufacturers identify “bank1” vs. “bank2” and “front/rear” vs. “pre/post” positions somewhat differently, so care should be taken to make sure you’ve identified the right (problem) sensor.

• Unplug the wire ­connection, then spray penetrating lubricant onto the threaded connection.

• Use an appropriate oxygen sensor removal tool.

• Most oxygen sensors come with a special electrically conductive anti-seize compound applied to the threads, so it’s merely a matter of threading the new sensor into the void left by the old one.

• If the new sensor does not have anti-seize pre-applied, be sure to apply some to the threads prior to installing the sensor. Do not put excessive amounts of anti-seize onto the threads. Getting anti-seize compound on the sensing area will contaminate it.

• Always check the appropriate reference material for the required torque specification. Once it’s snug, plug the connector into the vehicle’s factory wiring to finish the task.

• Using Mode $06 Test Data

– Once an oxygen sensor repair is made, Mode $06 data can be useful to determine if the oxygen sensor is operating correctly and the repair was effective.

– Mode $06 is the actual system test data that OBD II looks at when it decides to set a pending or current fault code.

• The chart below is an example of the Mode $06 data that can be obtained with regard to the oxygen sensors.

Courtesy of Delphi Product and Service Solutions.



You May Also Like

How To Diagnose Slow or Sluggish Oxygen Sensors

When oxygen sensors are tested, manufacturers will introduce small amounts of oil to measure sensitivity.

An engine management system is always trying to find the perfect air/fuel ratio. But it is next to impossible to walk the line between too rich or too lean. With every revolution of the crankshaft, small changes in the air, fuel and operating conditions can cause changes to the oxygen content coming out of the exhaust port.

E-15 Ethanol Damage to Fuel Pumps

One of the problems with ethanol is how it reacts to water in the air and in the tank.

Oxygen Sensor Questions Answered

If an O2 sensor is not reading properly or is borderline, it should be replaced regardless of its age or mileage.

Managing (DPF) Diesel Particulate Filter Regeneration Cycles

The DPF is designed to store the soot and ash, to later burn them off during a regeneration cycle.

Ultimate Underhood – Gasoline Particulate Filters

Just like a DPF, a gasoline particulate filter (GPF) traps and stores soot particles in the exhaust stream.

Other Posts

U.S. House Schedules Vote to Stop EPA Emissions Mandate

The bill would prohibit the EPA from finalizing federal emissions standards for light- and medium-duty vehicles model years ’27 to ’32.

Forecast: 80% Drop In U.S. Transportation Emissions By 2050

NREL says rapid adoption of zero-emission vehicles is critical to reduce emissions.

Understanding Emissions

Modern EVAP systems are selective with how they vent vapors back into the engine. Sponsored by Standard.

Domestic Gasoline Engine Oil Specifications

If it’s been more than a year since last oil change, the IOLM will display a reminder message, regardless of mileage.