1. 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

2. 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. 4

3. 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! 

4. 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 amps or less.
PCM converts the current output into a voltage signal to be read on a scan tool.

5. Comparison of signals
Regular o2 outputs voltage
WRAF outputs CURRENT

6. 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.

7. Current Flows! to maintain voltage!
Voltage created by PCM for the scan tool!
The voltage measured at the A/F sensor will remain constant and will not match the scan tools display. The Voltage shown on the scan tool is created by the PCM for OBDII Diagnostics. Amperage is the measurement!
an oxygen pump pulls oxygen from the exhaust into a diffusion gap to maintain a constant Voltage.
Creating AMPERAGE!
.020 amps 4

8. 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! 4

9. 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 4

10. 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.

11. Honda’s Looks like regular O2 5 wires or 6 Dual Nernst Cell
1200˚F operation temp
Recommends scan tool for diagnosis 4

12. 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 4

13. 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.

14. Toyota Testing a. Disconnect the A/F sensor connector.
b. measure the resistance between terminals +B and HT.
Resistance: * ohms at 20°C (68°F).
2007 FJ 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.

15. Toyota’s sensor output is not a changing analog voltage, but rather a small (< amps) bi-directional current.
LEAN
Negative Amperage
RICH
Positive 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 sensor’s two signal lines does not change.

16. 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

17. Verify Proper Operation - Toyota A/FS

18. 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

19. 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.

20. Testing a Bosch Check Heater Circuit for Current or Voltage
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 ohms.
Reconnect harness , use DVOM check reference ground,
Bosch spec is volts (refer to actual specs)

21. 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.

22. 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.

23. Nissan Maxima 2004

24. Infiniti 2008 EX35

25. 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

26. 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).

27. 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
Alflash.com.ua photos by al tech page
Toyota Wide Range Air:Fuel Sensor,
John Thornton, Underhood Service, January 2002