Honda o2 Sensor Training

7/28/2019 Honda o2 Sensor Training

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LAF Sensor

Jim MooreASPIRE Inc.


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Authored by: Joseph Marchesani Copyright 1996 Aspire Inc. 2

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


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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 calledelectrodes

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.


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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


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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 Zirconiaelements

The air reference is at the other end


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Lean Air Fuel

The LAF sensor has two Zirconia elements

that share a diffusion chamber

The LAF sensor is actually two O2 sensorsin one

One Zirconia element acts as an oxygen

pump


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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 electronscauses a flow of ions, charging the battery


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4.3K


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LAF Sensor Operation

To distinguish the two Zirconia we will call

them S1 and S2

The ECM monitors the voltage between S1input 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


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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


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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


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S2 now pumps oxygen into the diffusion

chamber from the air chamber

The voltage between S1 input and ground isheld to 450 mV

The ECM can determine how rich or lean

the exhaust is by monitoring the amperage ittakes S2 to maintain 450 mV on S1 input


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On a standard O2, sensor 450 mV indicates

14.7:1 AF/R

On the LAF sensor, the exhaust is at aknown 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


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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 terminaland again to the sensor ground to monitor

the 450 mV


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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 thescope display


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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 voltageshould go negative record the reading

Remove the propane quickly, the voltage goes

positive


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