1. LAF Sensor
Jim Moore
ASPIRE Inc.

2. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
Honda LAF Sensor
Allows the stoichiometric 14.7:1 AF/R under some conditions
But can monitor AF/R over a much greater range
This allows it to operate at as lean as 23:1
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
Authored by: Joseph Marchesani

3. Zirconia O2 Sensor Operation
The Zirconia O2 Sensor used on most vehicles operates in a very small window about .3% above and below 14.7:1AF/R
A thimble shaped Zirconia element has two sides called electrodes
The inside of the thimble is the reference air chamber or where the positive lead connects, vents to ambient air.
The outside of the thimble is exposed to the exhaust side and connects to the sensor ground.
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

4. Zirconia O2 Sensor Operation
In a chemical battery a flow of ions internally causes a flow of electrons outside the battery
In the O2 sensor thimble the oxygen ions that flow through it create the return signal
Oxygen ions are oxygen atoms with a charge
Outside air has more oxygen than the exhaust creating an ion flow and eventually the O2 signal
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

5. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
By controlling the O2 in the diffusion chamber you control the operating range
Chamber one is outside the chamber in contact with the exhaust
Diffusion Chamber is between the Zirconia elements
The air reference is at the other end
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

6. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

7. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
Lean Air Fuel
The LAF sensor has two Zirconia elements that share a diffusion chamber
The LAF sensor is actually two O2 sensors in one
One Zirconia element acts as an oxygen pump
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

8. What do we mean when we talk about an oxygen pump?
Remember a flow of ions creates a flow of electrons
The inverse is also true, a flow of electrons causes a flow of ions, charging the battery
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

9. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
4.3K
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

10. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
LAF Sensor Operation
To distinguish the two Zirconia we will call them S1 and S2
The ECM monitors the voltage between S1 input and the ground lead
It tries to hold the voltage difference between S1 and ground to 450 mV
When the mixture goes rich, oxygen ions flow from the diffusion chamber to the exhaust
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

11. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
LAF Sensor Operation
The voltage on S1 input increases
The ECM detects the change and reduces voltage on S2 input
This causes the voltage on S2 to go more negative than the ground voltage
This causes S2 to pump oxygen out of the diffusion chamber to the air chamber
At the same time the ECM drops voltage on S2 input, its also reducing fuel delivery
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

12. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
LAF Sensor Operation
As the mixture goes leaner, oxygen ions flow from the exhaust into the diffusion chamber
The voltage on S1 input decreases
The ECM sees the voltage drop and increases the volt to S2 input
The voltage on S2 is now more positive than the ground voltage
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

13. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
LAF Sensor Operation
S2 now pumps oxygen into the diffusion chamber from the air chamber
The voltage between S1 input and ground is held to 450 mV
The ECM can determine how rich or lean the exhaust is by monitoring the amperage it takes S2 to maintain 450 mV on S1 input
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
Authored by: Joseph Marchesani

14. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
LAF Sensor Operation
On a standard O2, sensor 450 mV indicates 14.7:1 AF/R
On the LAF sensor, the exhaust is at a known value when S1 is at 450 mV
When S1 is at 450 mV and S2 is at zero volts, the mixture is at 14.7:1 AF/R
If S2 is negative its richer than 14.7:1
If S2 is positive its leaner than 14.7:1
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

15. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
Testing the LAF sensor
Hook a DSO positive lead to the S2 (white wire) of the LAF sensor and the ground lead to the LAF sensor ground (black wire)
Do not use a vehicle ground you will see nearly 2.7 volts when hooked up this way
A DMM could be hooked to the S1 terminal and again to the sensor ground to monitor the 450 mV
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

16. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.
Testing the LAF sensor
DSO settings
Voltage Scale: 500 mV per division
Time Base: 200 mS per division
Trigger Level: Auto on
Trigger Slope: Either way
Put the zero voltage level in the middle of the scope display
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

17. Verifying the LAF sensor
Be sure the engine is hot and the LAF sensor is fully warmed up run at 2000 RPM
Enrich with propane the LAF sensor voltage should go negative record the reading
Remove the propane quickly, the voltage goes positive
Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.

18. Authored by: Joseph Marchesani Copyright 1996 Aspire Inc.