WS6

Oxygen Sensors on Vehicle

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

• The oxygen sensors are located directly in the exhaust system, on the left hand side of the engine on the exhaust manifold.
  1.2 How many wires for this oxygen sensor? ……three wires ………
  1.3 Record the colors 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 colors. You may
  have to consult a wiring diagram.
     
  Colour Use or Purpose
  White …Power supply
  

  White ...Signal

  Black … Ground

  
  

  1.4 What type of Oxygen Sensor is this? 

  Zirconia switching sensor

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

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

  This worksheet is designed for switching type sensors only. If

  you have a broadband sensor, see your lecturer for another

  worksheet.

  2.0 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 …yes ok……………….

  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?......0.8V...........

  3.3 How low does the voltage go? ……0.2V……….

  3.4 What is the average voltage? (Some oscilloscopes have

  functions that will calculate the average for you. If not, just

  guess.)……up to 5V………….

  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: …7………..

  
  
  

  
  

  The highest voltage I got was 0.85 Volts which was within manufaturer specs. each division is 0.5 Volts and time is 1 second.

  
  

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

  does:

  The cycling is normal.

  
  

  
  

  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.

  

  
  

  4.2 How high does the voltage go? …0.66V…………

  4.3 How low does the voltage go? ……0.84V………

  4.4 What is the average voltage? (Some oscilloscopes have

  functions that will calculate the average for you. If not, just

  guess.) …0.5V………

  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: ……12……

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

  does:

  Cycling is normal.

  
  

  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? 782V

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

  does:

  The voltage goes high when we do a sudden acceleration, the voltage increasing from  less than 0.2V to higher than 0.8V in less than 100ms.

  
  

  
  

  
  

  6.0 Make this Oxygen Sensor go lean by doing a sudden

  deceleration. Gently run the rpm up to about 3,000, and let the

  RPM drop suddenly. The fuel system should make the system

  go lean on deceleration. The signal should go below 0.2V.

  6.1 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.

  
  

  
  
  

  

  
  

  
  

  6.1 How low does the Oxygen sensor voltage go?..0.006V.......

  6.2 If this signal is not going low normally, describe what the signal

  does:

  The voltage goes down when we do a sudden deceleration,this sensor is in good working condition as all the results were within the specifications.

  
  

  
  Measure the Response Time of the sensor. You want to know
  that the sensor can respond quickly to changes in the exhaust gas.
  The best way is to do a sudden acceleration, freeze the pattern, and
  measure how long it took the sensor to go from lean to rich.
  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 0.2V to above 0.8V. in less than
  100 ms. Note the voltage and time per division or scale next to
  the graph.
  7.2
  
  

  

  7.2 Measure how long the sensor took to go from lean to rich.

  Use the cursers on the scope if necessary. Record how long

  the sensor took here: 0.005 volts