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-range, WRAF Wide-band, WAFR
Linear Air Fuel, A/F
Lean Air/Fuel, LAF
Air Fuel Ratio Sensor, AFS
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.
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.
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.
Neat Russian Graphics!
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
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.
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.
Heater Circuit pattern
“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.
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
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).