Lambda Sensors |

Lambda Sensors Lambda Sensors Q&A
Frequently Asked Questions answered by the DENSO technical team
Q1: What role do Lambda Sensors play?
A: In order to reduce emissions, modern cars have been designed
to carefully control the amount of fuel they burn. The Lambda (or
Oxygen) Sensor is a critical component in this process, Its goal
is to work together with the car’s fuel injection system, catalytic
convertor and electronic control unit (ECU) (Fig. 1) to achieve the
lowest possible output of environmentally harmful engine emissions.
The Lambda Sensor does this by monitoring the percentage of
unburned oxygen present in the car’s exhaust gases. This data is fed
to the car’s ECU, which adjusts the A/F (air/fuel) mixture. The correct
air/fuel mixture enables the Catalytic Converter to run efficiently.
This ‘exhaust gas cleaning system’ removes as many of the harmful
emissions as possible from the exhaust before it leaves the car.
Q2: Where are the Lambda Sensors positioned?
A: Every new car, and most cars manufactured since 1980, has a
Lambda Sensor. It is positioned in the vehicle’s exhaust pipe before
the Catalytic Converter, where it measures the oxygen present in the
exhaust gases and informs the ECU, enabling the ECU to calculate
what adjustments are needed to the air/fuel mixture. The exact
location of the Lambda Sensor varies according to whether the
vehicle has a V-type or In-line type exhaust system, and depending
on make and model. Some typical engine mounting configurations
are shown in the LOCATION section of this catalogue.
Q : How exactly do Lambda Sensors work?
A: Lambda Sensors work together with the vehicle’s fuel injection
system, Catalytic Converter and engine management system or
electronic control unit (ECU) (Fig. 1) to help achieve the lowest
possible output of environmentally harmful engine emissions:
> The Lambda Sensor monitors the percentage of unburned oxygen
present in the car’s exhaust gases.
> According to whether the oxygen content in the exhaust gas is too
high (a lean mixture) or too low (a rich mixture) the Lambda Sensor
transmits a fast-changing, fluctuating voltage signal to the ECU.
> The ECU responds to this information by adjusting the air/fuel
mixture entering the Catalytic Converter. The goal is to keep the
air/fuel ratio very close to the ‘stoichiometric’ point, which is the
calculated ideal ratio of air to fuel entering the Catalytic Converter.
Theoretically, at this ratio, all of the fuel will be burned using
almost all of the oxygen in the air. The remaining oxygen must be
exactly the right quantity for the Catalytic Converter to function
efficiently.
> The Catalytic Converter then treats the exhaust emissions before
they leave the car. Most modern cars are equipped with a threeway
Catalytic Converter. ‘Three-way’ refers to the three regulated
(harmful) emissions it helps to reduce - Carbon Monoxide (CO),
unburnt Hydrocarbons (HC), and Nitrogen Oxide (Nox) molecules.
The exact amount of oxygen in the exhaust gasses is important
to the Catalytic Converter because it affects how well it is able
to remove these harmful emissions from the exhaust gases. The
right amount of oxygen enables a chemical reaction to take place
between the harmful gases and the oxygen, resulting in harmless
gases leaving the Catalytic Converter.
If the converter is working correctly, all the oxygen in the exhaust
gases will be consumed by this chemical reaction.
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Fig. 1: Engine with Sensors and Catalytic Converter.
1. Fuel Injector
2. Pre Cat Lambda Sensor
. Catalytic Converter
. Post Cat Lambda Sensor
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