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Another creative and educative information to our esteemed readers. Proper understanding of the operations of vehicle components/systems makes a fix easy, they include Control Modules, Sensors, Actuators, Spare Parts and other vehicle essential fluids. The understanding of their operation and functions makes it easy to pinpoint when things are going wrong and this will stem any eminent breakdown or accidents.

Oxygen Sensor in action

Air-fuel sensors and Oxygen sensors(O2) are designed to measure the amount of oxygen in the residual gases as they travel through the exhaust system after combustion, they are mounted on the exhaust manifold to mainly monitor how much unburned oxygen is in the residual gases as it exits the combustion chamber. 
Monitoring oxygen levels in the exhaust is a way of gauging the fuel mixture. It tells
the computer if the fuel mixture is burning rich (less oxygen) or lean (more oxygen). A lot of factors can affect the relative richness or leanness of the fuel mixture, including air temperature, engine coolant temperature, barometric pressure, throttle position, air flow and engine load. 

Tools required to remove O2
There are other sensors to monitor these factors, but the O2 sensor is the master monitor for what’s happening with the fuel mixture.

Consequently, any problems with the O2 sensor can throw the whole system out of balance. 
There are two types of oxygen sensors namely the air-fuel sensor and the oxygen sensor, the first measures precisely the amount of oxygen in the exhaust gas rather than switching from Rich to Lean as done by the latter. 

Bi-section on the Oxygen sensor and lable
For this singular reason their features are very different. The Air-fuel oxygen sensors are: Advanced Wideband sensing element for exact air/fuel measurement, Robust sensor design increases sensor longevity, Seared protection tube due to 100% functional quality test, True Direct-fit, OE connectors and harness, Pre-coated threads with anti-seize compound right out of the box. 

Real Picture at our workshop
They use a more sophisticated sensing element that provides a signal to the vehicle’s ECU that is proportional to the amount of oxygen in the exhaust, while the regular Oxygen sensors are: Double laser-welded stainless steel body to protect against contamination,
Seared protection tube due to 100% functional quality test, Pre-coated threads with anti-seize compound right out of the box, True Direct-fit OE connectors and harness, though oxygen sensors are thimble and planar switching sensors that are designed to meet or exceed OE specifications. 

Same here
This brings to fore the reason why detailed understanding of the component and their operational parameters are important, it removes the risk of buying the wrong components when the need arises.


OPERATION
: The O2 sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is coated on the outside with a porous layer of platinum. 

How to reconnect a cut wire
Inside the bulb are two strips of platinum that serve as electrodes or contacts. The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors “breathe” through their wire connectors and have no vent hole. 
It’s hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). 
Venting the sensor through the wires rather than with a hole in the body reduces the
risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail.The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading. 
An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor’s output voltage will drop down to about 0.1 volts. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7 to 1, the sensor will read around 0.45 volts. When the computer receives a rich signal (high voltage) from the O2 sensor, it leans the fuel
mixture to reduce the sensor’s reading. When the O2 sensor reading goes lean (low voltage), the computer reverses again making the fuel mixture go rich. This constant flip-flopping back and forth of the fuel mixture occurs with different speeds depending on the fuel system. 

Connector
The transition rate is slowest on engines with feedback carburetors, typically once per second at 2500 rpm. Engines with throttle body injection are somewhat faster (2 to 3 times per second at 2500 rpm), while engines with multiport injection are the fastest (5 to 7 times per second at 2500 rpm). The oxygen sensor must be hot (about 600 degrees or
higher) before it will start to generate a voltage signal, so many oxygen sensors have a small heating element inside to help them reach operating temperature more quickly. 
The heating element can also prevent the sensor from cooling off too much during prolonged idle, which would cause the system to revert to open loop. Heated O2 sensors are used mostly in newer vehicles and typically have 3 or 4 wires. 
Older single wire O2 sensors do not have heaters. When replacing an O2 sensor, make sure it is the same type as the original (heated or unheated).
CASE STUDY: 2009 Honda CR-V 2.4L L4 engine MIL ON with code P0135 (A/F sensor (sensor 1) Heater Circuit Malfunction) on a client’s vehicle. 
We had done our pin point test on this particular sensor before while diagnosing the vehicle; for those familiar with the sensor you know it can be accessed from the vehicle underneath. 
Just to throw you back to what we had while doing our pin point test, the A/F sensor had a mA current PID stuck on 0.03mA after the Coolant temperature PID was reading above 97 degree Celsius and this value was same at all RPM; hence the Fuel System will constantly be on Open loop and the Fuel Trims (STFT and LTFT will remain Flat at 0%). 
One common characteristic of a failed A/F Sensor or Heated Oxygen Sensor is that there will be a notable drop in your Fuel economy, this is so because the Sensors that failed are ‘Sniffers’-the nose with which the ECU detects when the exhaust gases are Lean or Rich. 
Without them, the ECM assumes the engine needs more Fuel and to keep it running he commands the Injector to give more Fuel (hence the reason for the excessive Fuel
consumption), this is the Air and Fuel delivery Fail-Safe-Strategy adopted by most vehicles.

While doing the diagnosis and pin point test we also made a new discovery, A/F Sensors, unlike the Heated Oxygen Sensor, do not oscillate up and down but will vary to be either Lean or Rich and stay steady.

Secondly because it doesn’t oscillate in voltage, its value remain constant but the current can be measured in milli-Amps. Hence the Scanner will read the A/F Sensors currents easily than a DVOM.


We fixed this fault by replacing the A/F Sensor 1 with an OEM replacement part and we scanned to read the Live Data. WOW! 
You might be curious why no codes were cleared, modern vehicle or Y2K Vehicles are
intelligent enough to know when this is electrically faulty or Fixed.
No need for clearing any code, the ECU will do a Comprehensive Component Monitoring and self learning at KOEO and KOER, spots the new sensor and turns off the MIL. 
Live Data gave us STFT -8%, LTFT 3%, A/F Sensor 0.4mA; Heated Oxygen Sensor
390mV. That’s a real fix! Signs of a worn out/damaged Oxygen sensor. 
1. Check engine light. 2. Lower fuel efficiency. 3. Drivability issues. 4. Harmful exhaust emission. 5. Catalytic converter damage. (P0430/ P0420) Physical examination of the sensor on removal. 
If the sensor has a greenish, grainy discoloration this indicates that the antifreeze is entering the combustion chamber. 
If the sensor is blackened with oily contamination, it implies that your engine is consuming excess engine oil. 
If the sensor has a dark brown discoloration, it implies the air-fuel mixture is too rich. 
If the sensor has a reddish or white discoloration, it implies that there is additives in the fuel. 
Once any of these signs are noticed, check the related system/component first before replacing the oxygen sensor because the fault could be from the related components/system.

Thanks for reading and I hope you found the information helpful.

Diagram are snap shots from Alldata and while working in our workshop.

Once again Understanding will birth easy fault fixing.


Be a Fixer and not a fitter!!! Stay Dirty…
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