The Basics in Determining the Efficiency of the Oxygen Sensors
The key to a well functioning oxygen sensor (or any car part for that matter) all boils down to proper maintenance and care. Hence, a regular inspection of the oxygen sensors need to be conducted by the car owner, preferably guided by a professional mechanic at first, so that its condition will be observed visually too.
When it comes to inspecting the oxygen sensors, an oscilloscope is best used to “test the sensor’s ability to respond to changes in the exhaust content”. This special device will help during the engine performance service. It also measures the response time of the sensors, and it will be able to provide a more “definitive diagnosis”.
There are a few tips on how to determine the efficiency of the oxygen sensors. At the same time, these will also determine if the O2 Sensors are able to respond accurately to rich and lean conditions. This will be applicable to any O2 sensor at all, for instance your Mercedes-Benz Oxygen Sensor. Hence:
-Connect the oscilloscope leading to the oxygen sensor circuit. For vehicles that use a three or four-wire heated O2 sensor, bridging the connector that leads and tap into the signal wire with an appropriate test probe at the connector plug may be needed.
-Warm the engine to operating temperature, meaning, at least 350 degrees F or 600 degrees C. Run the engine at about 2500 rpm for two or three minutes to heat up the sensor.
-Hold engine speed at a steady, high idle between 1200 and 2000 rpm.
-Artificially drive the system rich (using propane) and lean (by opening the brake booster hose) as you observe the oscilloscope voltage reading. It should peg from .800 to .900 volt (full rich) to .100 to .200 volt (full lean).
Achieving the minimum and maximum sensor voltages are just a part of the picture. How fast these transitions occur is an equally important measure of O2 sensor health. Lean-to-rich and rich-to-lean transitions should occur in 300mS or less. If it is greater than that, this may indicate a worn or contaminated sensor.
After achieving this, all O2 sensors must be heated now. Heat can contribute to the oxygen sensor’s longevity, since it can be placed further downstream in the car’s exhaust system. This will greatly protect the sensor from any possibility of having thermal shocks that are often caused by the heating and cooling cycles of the engine. Another advantage of having heated sensors is that they can easily reach operating temperature and immediately start producing a sensing voltage without having to wait for the heat of the exhaust to warm them.