Oxygen Sensor

An oxygen sensor,is an electronic device that measures the proportion of oxygen (O₂) in the gas or liquid being analyzed.

1.1 Locate an oxygen sensor on your vehicle. Describe where it is located:

  It is located in the exhaust manifold or in the exhaust downpipe before the catalytic converter.

1.2 How many wires for this oxygen sensor?  4

1.3 Record the colours for each of the wires at the sensor side of the connector (not the ECU side of the connector).  Then list the use of the wires. Usually a black or blue wire will be the O₂ sensor signal, Grey may be the sensor ground. Heater power and ground are often white. But there may be other colours. You may have to consult a wiring diagram.

          Colour                           Use or Purpose                       

          White                                          Heater Positive (+)
          White                                          Heater Negative (-)
          Grey                                           Signal Negative (-)
          Black                                          Signal Positve (+)
      

1.4 What type of Oxygen Sensor is this? (tick one)

                   Zirconia switching sensor?                               ✓
                   Titania switching sensor?                                 …….

                   Broadband Air Fuel Ratio sensor? (one cell)  …….

                   Broadband Air Fuel Ratio sensor? (two cell)  …….

2.0 Now we Back probe the Oxygen Signal Wire with a pin and connect to an oscilloscope. If you need help using the oscilloscope see your lecturer or other help sources. Check that you are connected to the Oxygen sensor signal: Run the engine and check that you are seeing a signal. Connected OK? Yes  ✓

3.0 Watch and Record Oxygen Signal pattern at 2500 rpm. Let the engine warm up and enter closed loop so you see a normal cycling pattern. You may have to hold the rpm about 2500 for half a minute to go into closed loop.

         

3.1 Freeze your pattern and draw or photograph it onto the graph below: Note the voltage and time per division or scale next to the graph.

3.2 How high does the voltage go? 0.869v

3.3 How low does the voltage go?  0.139v

3.4 What is the average voltage? 0.475v

3.5 How many “Cross Counts” does the signal have in 10 seconds? (One cross count is when it goes from high to low, or from low to high.) List here: 25 (at 2700 RPM)

3.6 If the signal is not cycling normally, describe what the signal does:

         If it Misfires in one cyclinder , the cycle will have dips in it. 

         

4.0 Watch and Record Oxygen Signal pattern at Idle rpm. Let the engine warm up and enter closed loop so you see a normal cycling pattern. You may have to hold the rpm about 2500 for half a minute to go into closed loop. Then let the RPM come down to idle.

4.1 Freeze your pattern and draw or photograph it onto the graph below: Note the voltage and time per division or scale next to the graph.

4.2 How high does the voltage go? 0.9v

4.3 How low does the voltage go?  0.119

4.4 What is the average voltage? (Some oscilloscopes have functions that will calculate the average for you. If not, just guess.) 0.475v

4.5 How many “Cross Counts” does the signal have in 10 seconds? (One cross count is when it goes from high to low, or from low to high.) List here: 10

4.6 If the signal is not cycling normally, describe what the signal does:

          It may have a negative pattern on the graph .

          5.0 Make this Oxygen Sensor go rich by accelerating once or twice. (The fuel system should normally make the system go rich when you do a sudden acceleration.) Push on the accelerator quickly but don’t let the rpm go high enough to hurt the engine. (If you act like you will hurt the engine you will be asked to leave lab.) The signal should go over 0.85V.

         

5.1 Freeze your pattern as it goes rich and draw or photograph it onto the graph below: Note the voltage and time per division or scale next to the graph.

          5.2 How high does the Oxygen sensor voltage go? 1 V         

5.3 If this signal is not going high normally, describe what the signal does: 

        It will have a very low voltage and it will be lower than 1.0 volt.
 

   6.0 Make this Oxygen Sensor go lean by doing sudden deceleraton. Gently run the rpm to about 3000 , and let the rpm drop suddenly. The fuel system should make the system go lean on deceleration. The signal should go below 0.2 V


6.1 Freeze your pattern as it goes rich .

6.1 How low does the oxygen sensor voltage go? 0.015 V
6.2 If this signal is not going low normally , describe what the signal does:
The signal will be above zero volts , might be a slugish oxygen sensor

7.0 Measure the Response Time of the sensor. freeze the pattern and measure how long it took the sensor to go from lean to reach.
7.1 freeze your pattern as it goes suddenly rich from a lean condition and draw it into the graph below . Normally you want the voltage to go from below 0.2 V to above 0.8V. In less than 100 ms .

7.2 Measure how long the sensor took to go from lean to rich. Use the sensors coursers on the scope if necessary. Record how long the sensor took here: 1.50 ms

8.0 Discusses how a normal Zirconium oxygen sensor works: draw a picture below to help show how it works?Zirconium oxygen sensor has two electrodes which provide an output voltage corresponding to the quality of oxygen in the exhaust in relation to the atmosphere. The output of 0.2 V represent a lean mixture. The Zirconia oxygen sensor technology operates though a known voltage being generated through oxygen interaction with the ziconium when it is heated to over 700ºC.

9.0 Discuss how good or bad this oxygen sensor is. What about it function well or is faulty? Use detail and specific voltage in your discussion. Can it accuratelly tell the ECU how rich or lean the exhaust is?


This sensor elements the rich/ lean cycling allowing the control unit to adjust the fuel delivery and ignition timing of the engine much more rapidly, but less sensitive to either rich or lean. 0.2 volts represent lean and 1 volt represent rich mixture.

Exhaust Emissions

Exhaust gas is emitted as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel fuel, fuel oil or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack or propelling nozzle


Exhaust Analyser should be warmed up and recently calibrated. When it’s time to start taking tailpipe readings, put the analyser probe into the tailpipe and install exhaust tube over probe to capture exhaust fumes. Make sure there is adequate ventilation.

Note: make sure you fill out the “means: .............  segment to explain what that gas reading means. Example, if you are measuring HC, which shows us about misfire in the engine, and you had a low number like 28 ppm, you would say “shows low amount of misfire”, or “most of the fuel is being burnt.” But if the HC was high, like 340 ppm, you might say “There is a high amount of misfire” or “not all the fuel is being burnt.”

1.         With the analyser probe sensing normal air, what are the Four Gas readings? Record the amount and then what it means:

CO 0.001   means: Control rich conditionsHC 12ppm  means:  Higher HC means that unburn fuel remains in the exhaust gases.CO2 0.00%means: EfficencyO2 20.90   means:  It is lean

2.         Start the engine idling cold, and record the Four Gas readings

Explain what is happening within the engine referring to the four gases:    

CO 2.5%  HC 788  CO2 12.6  O2 5.15. 

When the engine starts  cold , the CO increase to 2.5%. This means that rich mixture enters the combustion chamber. The HC also goes up significantly and unburn fuel remains in the exhaust gases. The CO2 (efficency) is low and the O2 is high from the inactive catalytic converter.  

        

3.    When the engine has warmed up, record the Four Gas readings:

Explain what is happening within the engine referring to the four gases:      

CO 0.58  HC 235  CO2 14.2  O2 1.10 

When the engine is warmed up, the CO & HC decrease. This means that the ideal mixture enters the combustion chamber. The CO2(efficency) is high and the O2 is low because the catalytic conver well operates for cleaning the emissions.

4.    Run the warm engine at 2500 RPM, record the Four Gas readings:

Explain what is happening within the engine referring to the four gases:      

CO 2.5  HC 434  CO2 10%  O2 1.3 

When the engine is running warm at 2500 rpm, the CO and HC are more produced than the engine idling due to higher RPM with more emissions. However, the CO2 and O2 are still similar to idling condition.

5.         At idle, run the mixture rich with extra propane, LPG, or carburettor cleaner,  and record the Four Gas readings:

Explain what is happening within the engine referring to the four gases:      

CO 0.96  HC 224pmm CO2 225  O2 1.08 

 At idle,we had disconnected the vacuum hose in the fuel regulator for the rich condition. The CO increases to 0.96 which means the state of rich mixture. The unburn fuel is more produced due to more fuel injection.  

6.    At idle, create a lean condition with an air leak or vacuum leak, record the Four Gas readings:       

    Explain what is happening within the engine referring to the four gases:        

CO 0.069  HC 736  CO2 16.75  O2 11.30. 

At idle, We disconnected  the PCV valve for the lean condition. The CO recovers the nomal condition. The unburn fuel goes up at 470ppm. The CO2(efficency) is reduced but the O2 increases significantly which means the state of lean mixture. 

7.    Accelerate the engine, by blipping the throttle a few times (don’t rev too high anddamage the engine), and watch how the gas readings change.  Record the Four Gas readings when the CO is highest: 

    Explain what is happening within the engine referring to the four gases:        

CO 2.547 HC 699 CO2 10.54  O2 2.52
 From the sudden acceleration, the rich mixture is supplied into the combustion chamber. The CO and HC rise. The CO2(efficency) is reduced but the O2 increases slightly due to more fuel injection with more intake air.  
8.    Disconnect one spark plug wire, ground it with a jumper wire, then record the Four Gas readings as the engine idles:

     Explain what is happening within the engine referring to the four gases:       

CO 0.01  HC 10.33  CO2 13.6  O2 453 

When the misfire is produced in a cylinder, the HC increases dramatically because the unburn fuel is created by the misfired cylinder. The O2 is also produced more from the air/fuel mixture of the misfired cylinder.

9.    If you can get to it, disconnect the injector harness connector from one injector on an engine that has one injector for every cylinder: Record the Four Gas readings as the engine idles:

Explain what is happening within the engine referring to the four gases:      

CO 0.047  HC 225  CO2 12.09  O2 4.75 

When the injector is disconnected, the HC is normal because the fuel does not injects into the intake port. However, the O2 increases due to the air is still supplied into the combustion chamber

10. Optional: Make other changes to the engine at idle, such as turning on the air conditioning or rocking the steering wheel.  Note the change you made: 

    Explain what is happening within the engine referring to the four gases:        

CO 0.049  HC 74  CO2 15.34  O2 0.12

Overall, the emission is clean with proper values. However, when loads (air conditioning and rocking the steering wheel) are added, the rpm will go up. As a result , the CO and HC increase slightly with the rich condition.  

Return the vehicle to good condition and proper adjustment.

11.      Explain the different readings you would get from a vehicle with a catalytic converter and a vehicle without one and why?

I would get the differnt readings. If the vehicle does not have a catalytic converter the emission will be exhausted without any filtering. The catalytic converter helps reducing emissions with its chemical actions.

12.      Explain what light off point means and what happens?

 When the temperature is hot enough, the catalytic converter will clean the emissions with its operating temperature.

13.       On lambda, 02 sensors why do they have 1,2,3,4 or 5 wires and what do these extra wires do?

From two white heater positive and negative, the O2 sensor works correctly and increases responses with operating temperature when the engine starts with cold conditions. The black wire is a snesor signal positive which gives the state of exhaust gases to the ECU. The gray wire is a sensor signal earth

         

Scan tool Diagnosics

1. Scan Tool Data

1.1       Find a vehicle which is appropriate for the scan tool.

1.2       Connect the scanner, power it on, follow the instructions and input the correct vehicle information it asks for so you can view the data.

1.3       Find the data for the information listed on the next page. Turn engine on to idle. Fill in the letters used to label the information and the value of that data. (For example, engine load information may be found under MAP, with a value of 3.6, listed in volts) Note: not all vehicles will support all information, just find as much as you can. If the engine won’t run, input the information with the key on, engine off.

Type of information (PID = Parameter Identification)	Letters to describe it E.g. TPS	Value of data	Units for data E.g. volts
Engine Load (how much air comes in)	Intake	15%	Percentage
Engine RPM	RPM	725	Revolutions per minute
Throttle angle	TPS	0.96v	Voltage
Engine coolant temperature	ECT	33°C	Degree Celsius
Intake air temperature	IAT	3.73
Fuel Injection opening pulse	FIOP	4.71	Ms
Transmission select position	-
Vehicle Speed	-	0	KM/H
Oxygen sensor(s)	O2	0.10-0.70v	Voltage
Fuel Trim	-
Idle control	IAC	43%	Percentage
Power steering Load		0.02v	Voltage
Air conditioning condition	AC	3.91	Voltage
Exhaust Gas Recirculation (EGR)
Fuel Evap or Purge condition
Malfunction Indicator Light (MIL)
Barometric Pressure		78	Hz

2             Trouble Codes or Fault Codes

2.1       Find where the Codes are listed

 

2.2       Record any codes, and what system and condition they describe in the chart below (Example: might be code number 21, for Throttle Position Sensor, signal voltage too low) If there are no codes listed, put “none”.

Code number	System affected	Condition described
NO CODE

3             Lecturer put in Fault

3.1       Find your lecturer and have him create a fault under the hood (don’t look)

4             Record New Codes

4.1       Look up the codes now in the scan tool

4.2       Record the codes in the chart below. Also record what system is affected, and what condition is described.

Code number	System affected	Condition described
PO113	Intake Air temp	High Input
PO100	MAP	High Input
PO122	TPS	Low Input

5             Find What Data Has Changed

5.1       Look through the scan tool data to see what PIDs (Parameter Identification of system voltages) have changed. Which readings don’t make sense or don’t read what you would expect. Concentrate on the PIDs related to the codes.

5.2       Record the PIDs that have changed below:

Type of information (PID = Parameter Identification)	Letters to describe it	Value of data	Units for data
Throttle Position Sensor	TPS	0v	Volts
Intake Air Temp	IAC	15°C	4.98
Engine Speed	RPM	825	RPM

6             Visual Inspection to find fault

6.1       Do a visual inspection under the hood to find where the problem is. Use information from the code to know where to look for the problem and what type of problem to look for.

Describe problem you found:

When the vacuum sensor is disconneted, the engine stops running.

7             Repair fault

7.1       Plug back in the connector, or repair problem found

7.2       Describe what you did:

Air Temp - 28°C  3.03v
TPS= 0.96v

8             Recheck Data PIDs

8.1       Recheck the data with the scan tool

8.2       Record the voltages for the PIDs related to the problem, to confirm they are back to normal

Type of information (PID = Parameter Identification)	Letters to describe it	Value of data	Units for data
Engine Speed	RPM	825	RPM
Coolant Tempurature Sensor	CTS	90	℃
Throttle Position Sensor	TPS	0	Volts
Intake Air Temp	IAC	15°C	4.98

9             Clear Codes 

Describe what you did to clear codes:

         

           I disconnected of the negative terminal  off the battery and took out  the engine main fuse for 30 seconds

10         Recheck for codes and record codes in system now:

         

 I rechecked the codes by selecting D.T.C, and there was no trouble codes on the screen.        

11      Discuss the importance live data when fault finding

It shows the state of the sensors from the live data values

12      Explain the need for parameters when checking live data

        

          when the fault is resolved, the live data will be rechecked with its parameters then the data should be compared to fault datas.

13     Discuss how a scan tool can aid you when fault finding

         

  I can find the fault easily now and although the vehicle is old or new, I can also check the state of a vehicle with various information.