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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. Wide-Band Oxygen Sensor. allows engines to operate as; Lean as 23:1 (40:1) Rich as 10:1 While maintaining closed-loop operation.

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wide band air fuel sensor

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

wide band oxygen sensor
Wide-Band Oxygen Sensor
  • allows engines to operate as;
    • Lean as 23:1 (40:1)
    • Rich as 10:1
  • While maintaining closed-loop operation.
  • more accurately reflects the oxygen content in the exhaust vs a conventional oxygen sensor.
comparison of signals
Comparison of signals
  • Regular O2 sensor only measures in a narrow band at 14.7:1
    • Worthless for low emission vehicles!
  • Wideband has a much “wider” band to measure from 10:1 to 20:1
    • Necessary for the new direct injection fuel systems
    • Necessary for clean air!
operation
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.

comparison of signals1
Comparison of signals
  • Regular o2 outputs voltage
  • WRAF outputs CURRENT
operation1
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.

current flows to maintain voltage
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

amperage
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 22:1, or leaner. (2.2 bar is 31.9:1)
  • Testing a wide-band oxygen sensor usually involves using a scan tool.

Neat Russian Graphics!

number of wires
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

laf conversions obdii scanners

LAF Conversions - OBDII Scanners

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.

Normalized OBDII Voltage is the data the PCM will show the scan tool

- It is not an actual measurement

honda s
Honda’s
  • Looks like regular O2
  • 5 wires or 6
  • Dual Nernst Cell
  • 1200˚F operation temp
  • Recommends scan tool for diagnosis
toyota a fs linear a f 4 wire
Toyota A/FS -Linear A/F 4 Wire
  • 1996 appearance
  • Looks like regular O2
  • 4 wires
  • Single Nernst Cell
  • 1200˚F operation temp
  • Recommends scan tool for diagnosis
linear a f signals
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.
toyota testing
ToyotaTesting

a. Disconnect the A/F sensor connector.

b. measure the resistance between terminals +B and HT.

Resistance: 0.8 - 1.4* ohms at 20°C (68°F).

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.

slide15
Toyota’s sensor output is not a changing analog voltage, but rather a small (< 0.020 amps) bi-directional current.
  • 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 sensor’s two signal lines does not change.

RICH

Positive Amperage

LEAN

Negative Amperage

toyota s intelligent tester
Toyota’s 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
bosch air fuel sensor
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
testing a bosch compare lambda
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.

testing a bosch
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)
testing a bosch1
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.
verify proper operation bosch lsu 4
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.

tech tips
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

tech tips continued
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).

references
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 Air:Fuel Sensor,
    • John Thornton, Underhood Service, January 2002