Wide-band Air Fuel Sensor

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Wide-band Air Fuel Sensor

• Wide-range, WRAF Wide-band, WAFR
• Linear Air Fuel, A/F

Lean Air/Fuel, LAF Air Fuel Ratio Sensor, AFS
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Wide-Band Oxygen Sensor

• allows engines to operate as
• Lean as 231 (401)
• Rich as 101
• While maintaining closed-loop operation.
• more accurately reflects the oxygen content in
  the exhaust vs a conventional oxygen sensor.

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Comparison of signals

• Regular O2 sensor only measures in a narrow band
  at 14.71
• Worthless for low emission vehicles!
• Wideband has a much wider band to measure from
  101 to 201
• Necessary for the new direct injection fuel
  systems
• Necessary for clean air!

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Operation
Amperage flows here!
Oxygen causes the Nernst cell to generate a
voltage just like an ordinary O2. The oxygen
PUMP Cell compares the change in voltage to the
control voltage from the PCM, balances to
maintain an internal oxygen balance. CURRENT
FLOW is altered creating a positive or negative
current signal that indicates the exact air/fuel
ratio of the engine. The current flow isn't much,
usually only about 0.020 amps or less. PCM
converts the current output into a voltage signal
to be read on a scan tool.
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Comparison of signals

• Regular o2 outputs voltage
• WRAF outputs CURRENT

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Operation
The volume ratio at 1 bar air-pressure would be
about 4500 liter air for 1 lb of fuel. 1 bar is
14.5 psi.
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Current Flows! to maintain voltage!
Voltage created by PCM for the scan tool!
an oxygen pump pulls oxygen from the exhaust into
a diffusion gap to maintain a constant
Voltage. Creating AMPERAGE! .020 amps
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Amperage!
When the air-fuel ratio is lean, the sensor
produces a positive current ranges from zero to
2.0 milliamperes as the mixture gets leaner up to
221, or leaner. (2.2 bar is 31.91) Testing a
wide-band oxygen sensor usually involves using a
scan tool.
Neat Russian Graphics!
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Number of Wires

• Lean Air-Fuel Ratio Sensors
• May uses 4, 5, 6, or 7 wires.
• Power wire
• 1 or 2 wires for the electric heater (power
  ground)
• 3 or 4 sensor wires

Current
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LAF Conversions - OBDII Scanners
Normalized OBDII Voltage is the data the PCM will
show the scan tool - It is not an actual
measurement

• Most PCMs display the rich and lean status of the
  exhaust,
• BE CAREFUL! many show the operation of the oxygen
  sensor in millivolts from zero to 1000 just as if
  the sensor were a conventional zirconia oxygen
  sensor. But it is not the actual sensor data.

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Hondas

• Looks like regular O2
• 5 wires or 6
• Dual Nernst Cell
• 1200F operation temp
• Recommends scan tool for diagnosis

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Toyota A/FS -Linear A/F 4 Wire

• 1996 appearance
• Looks like regular O2
• 4 wires
• Single Nernst Cell
• 1200F operation temp
• Recommends scan tool for diagnosis

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Linear A/F signals

• Heater pulse width
• Voltage reference signals 3.3v 3.0v
• Lambda value compared to rich lean
• Substituted HO2S values - slow minimal movement.

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ToyotaTesting

• a. Disconnect the A/F sensor connector.
• b. measure the resistance between terminals B
  and HT.
• Resistance 0.8 - 1.4 ohms at 20C (68F).
• 2007 FJ 1.8 - 3.4 ohms
• If the resistance is not as specified, replace
  the sensor.
• Torque 44 Nm (440 kgf.cm, 31 ft.lbf)
• c. Reconnect the A/F sensor connector.

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Toyotas sensor output is not a changing analog
voltage, but rather a small (lt 0.020 amps)
bi-directional current.
RICH Positive Amperage
LEAN Negative Amperage

• RICH exhaust produced a positive 4.89 milliamps a
  
• LEAN exhaust produced a negative 1.53 milliamps.
• The sensor has two signal lines. One line has 3.3
  volts, and the other has 3.0 volts on it
  (relative to engine ground).
• These two voltages do not change.
• Voltage (300 millivolts) across the sensors two
  signal lines does not change.

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Toyotas Intelligent Tester

• A/F CONTROL Change injection volume
• Lower 12.5 or
• increase by 25
• test at less than 3,000 rpm
• A/F CONTROL enables checking and graphing of
  A/F
• (Air Fuel Ratio) sensor and Heated Oxygen (HO2)
  sensorvoltage outputs
• To conduct test, select following menu items
• ACTIVE TEST / A/F CONTROL / USER DATA /
• AFS B1S1 and O2S B1S2,and press YES and ENTER

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Verify Proper Operation - Toyota A/FS
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Bosch Air Fuel Sensor

• Porsche says all 2010 models will be equipped
  with the new sensor!
• Diagnose with Factory scan tool.
• Compare lambda values on scan tool and emissions
  machine
• Watch valuse
• Create RICH
• Create LEAN

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Testing a Bosch compare Lambda
the Best way to diagnose this A/F ratio sensor
Scan tool Gas Analyzer, Lambda
values should should match, if not more
diagnostics will be required.
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Testing a Bosch
Heater Circuit pattern

• Check Heater Circuit for Current or Voltage
• Disconnect harness, check resistance of the
  trimming resistor, located on Input and Output
  pump current wires.
• Bosch spec is 30 - 300 ohms.
• Reconnect harness , use DVOM check reference
  ground,
• Bosch spec is 2.4 - 2.7 volts (refer to actual
  specs)

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Testing a Bosch

• 4. Scope the pump cell Nernst signal
• use sensor reference ground that you just
  checked.
• Set scope to AC-coupled mode to see negative
  swings
• Nernst voltage signal remains at .45 volts at all
  times
• Pump cell voltage should vary about .5 to .6
  volts switching across 0 volts
• Drive fuel mix rich then lean expect change in
  voltage of greater than 1.0 volts.

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Verify Proper Operation - Bosch LSU 4
Current pump sensor 60 seconds of road test
after replacement shows proper operation Check
Mode 6 Data
Pump cell pumps oxygen ions from one side of the
sensor to the other. PCM monitors the Nernst
signal attempting to keep the voltage at .45
volts. PCM will increase and decrease the
current flow to the pump cell to maintain that
voltage level.
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Nissan Maxima 2004
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Infiniti 2008 EX35
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Tech Tips

• TECH TIPS
• Honda 5-wire "Lean Air Fuel" (LAF) sensors, the
  8-pin connector pin for the sensor contains a
  special "calibration" resistor. The value of the
  resistor can be determined by measuring between
  terminals 3 and 4 with an ohmmeter, and will be
  2.4K ohms, 10K ohms or 15k ohms depending on the
  application. If the connector is damaged and must
  be replaced, the replacement must have the same
  value as the original. The reference voltage from
  the PCM to the sensor on these engines is 2.7
  volts.
• Saturn also uses a special trim resistor in the
  WRAF sensor connector (pins 1 6). The resistor
  is typically 30 to 300 ohms. The PCM supplied
  reference voltage is 2.4 to 2.6 volts.
• If a WRAF sensor has failed because of coolant
  contamination, do not replace the sensor until
  the leak has been repaired. The new sensor will
  fail otherwise.
• Some early vehicle systems caused a "simulated"
  voltage to be displayed on a scan tool. The
  actual value was divided by 5 to comply with
  early OBD II regulations. Those regulations have
  since been revised, but be aware if you get a
  "funky" display on your scan tool

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Tech tips continued
 

• variable current signal that can travel in one of
  two directions (positive or negative). The signal
  gradually increases in the positive direction
  when the air/fuel mixture becomes leaner. At the
  "stoichiometric" point when the air/fuel mixture
  is perfectly balanced (14.7 to 1), the current
  flow stops and there is no current flow in either
  direction. And when the air/fuel ratio becomes
  progressively richer, the current reverses course
  and flows in the negative direction.
• The PCM sends a control reference voltage
  (typically 3.3 volts on Toyota applications, 2.6
  volts on Bosch and GM sensors) to the WRAF sensor
  through one pair of wires, and monitors the
  sensor's output current through a second set of
  wires. The sensor's output signal is then
  processed by the PCM, and can be read on a scan
  tool as the air/fuel ratio, a fuel trim value
  and/or a voltage value depending on the
  application and the display capabilities of the
  scan tool.
• For applications that display a voltage value,
  anything less than the reference voltage indicate
  a rich air/fuel ratio while voltages above the
  reference voltage indicates a lean air/fuel
  ratio. On some of the early Toyota OBD II
  applications, the PCM converts the WRAF sensor
  voltage to look like that of an ordinary oxygen
  sensor (this was done to comply with the display
  requirements of early OBD II regulations).

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References

• Supersniffers Why Air/Fuel Ration Sensors
• Bob Pattengale, MOTOR.com Dec. 2005
• FJ Cruiser Service Manual, 2007, section ES-313
• ATTS Training, Import Computers, 2008
• Sam Bell, Ralph Birnbaum G Jerry Truglia
• Advanced Engine Performance Diagnostics,
• Halderman, 4th ed. 2009.
• Alflash.com.ua photos by al tech page
• Toyota Wide Range AirFuel Sensor,
• John Thornton, Underhood Service, January 2002