What is a lambda probe in a car and how to check it
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What is a lambda probe in a car and how to check it

Modern cars use special devices that allow the vehicle to meet environmental standards. Among such devices is a lambda probe sensor.

Consider why it is needed in the car, where it is located, how to determine its malfunction, and also how to replace it.

What is a lambda probe?

The Greek "lambda" in the engineering industry is used to denote the coefficient. In this case, this is the concentration of oxygen in the exhaust gases. To be more precise, this is the coefficient of excess air in the fuel-air mixture.

What is a lambda probe in a car and how to check it

To determine this parameter, a special probe is used that assesses the condition of the fuel combustion products. This item is used in vehicles with electronic fuel supply. It is also installed in machines whose exhaust system is equipped with a catalyst.

What is a lambda probe for?

The sensor is used for more efficient supply of air-fuel mixture. Its operation affects the serviceability of the catalyst, which neutralizes substances harmful to the environment in exhaust gases. It measures the concentration of oxygen in the exhaust and adjusts the operation of the fuel system.

For the efficiency of the engine, the air-fuel mixture must be supplied to the cylinders in the correct proportion. If oxygen is not enough, the mixture will be re-enriched. As a result, candles in a gasoline engine can fill in, and the combustion process will not release enough energy to rotate the crankshaft. Also, a lack of oxygen will lead to partial combustion of the fuel. As a result of this, carbon monoxide is not formed in the exhaust, but carbon monoxide.

What is a lambda probe in a car and how to check it

On the other hand, if there is more air than necessary in the air-fuel mixture, then it will be depleted. As a result, a decrease in engine power, exceeding temperature standards for parts of a piston-cylinder mechanism. Because of this, some items wear out faster. If there is a lot of oxygen in the exhaust, then NOx will not be neutralized in the catalyst. This also leads to environmental pollution.

Since the formation of toxic gases cannot be seen visually, a special sensor is required that would monitor even minor changes in the engine exhaust.

This part is especially useful in conditions of increased smoke generation (when the motor is under severe stress). This helps to keep the catalyst from pollution, as well as save a little fuel.

Lambda probe design

The catalyst zone sensor consists of the following elements:

  • Case made of metal. It has a turn-key thread made to make it easier to install or remove.
  • O-ring to prevent exhaust through a micro-slot.
  • Heat sink.
  • Ceramic insulator.
  • Electrodes to which wiring is connected.
  • Sealant wiring.
  • Heating element (in versions with heating).
  • Body. It made a hole through which clean air enters the cavity.
  • Spiral heating.
  • Dielectric tip. It is made of ceramics.
  • Protective metal tube with perforation.
What is a lambda probe in a car and how to check it

The main structural element is a ceramic tip. It is made of zirconium oxide. It is coated with platinum. When the tip heats up (temperature 350-400 degrees), it becomes a conductor, and the voltage is transmitted from its outer part to the inner one.

The principle of operation of the lambda probe

To understand what the malfunctions of the lambda probe may be, it is necessary to understand the principle of its operation. When the car is on the production line, all of its systems are tuned so that they work perfectly. However, over time, the engine parts wear out, minor errors may occur in the electronic control unit, which can affect the functions of different systems, including the fuel one.

The device is an element of the so-called “feedback” system. The computer calculates how much fuel and air to supply to the intake manifold so that the mixture burns out efficiently in the cylinder and enough energy is released. As the motor gradually wears out, over time the standard electronics settings are not enough - they need to be adjusted in accordance with the state of the power unit.

This function is performed by a lambda probe. In the case of an enriched mixture, it supplies a voltage corresponding to a value of -1 to the control unit. If the mixture is depleted, then this figure will be +1. Thanks to this adjustment, the computer adjusts the injection system to the changed engine parameters.

What is a lambda probe in a car and how to check it

The device works as follows. The inner part of the ceramic tip is in contact with clean air, the outer (located inside the exhaust pipe) - with the exhaust gases (through the perforation of the protective screen) moving through the exhaust system. When it is heated, oxygen ions freely penetrate from the inner surface to the outer.

There is more oxygen in the cavity of the sensor than in the exhaust pipe. The difference in these parameters creates the corresponding voltage, which is transmitted via wires to the computer. Depending on the change in parameters, the control unit adjusts the fuel or air supply to the cylinders.

Where is the lambda probe installed?

The sensor is not in vain called a probe, since it is installed inside the exhaust system, and captures indicators that cannot be analyzed during depressurization of the system. For greater efficiency in modern cars, two sensors are installed. One is screwed into the pipe in front of the catalyst, and the second behind the catalyst.

What is a lambda probe in a car and how to check it

If the probe is not equipped with heating, then it is installed as close to the motor as possible to heat up faster. If two sensors are installed in the machine, they allow you to adjust the fuel system, as well as analyze the effectiveness of the catalytic analyzer.

Types and design features

There are two categories of lambda probe sensors:

  • Without heating;
  • Heated.

The first category refers to older varieties. It takes time to activate them. The hollow core should warm up to operating temperature when the dielectric becomes a conductor. Until it heats up to 350-400 degrees, it will not work. At this point, the air-fuel mixture is not adjusted, from which unburned fuel can enter the catalyst. This gradually reduces the working life of the device.

For this reason, all modern cars are equipped with heated modifications. Also, all sensors are classified into three varieties:

  • Two-point without heating;
  • Two-point heated;
  • Broadband.

Modifications without heating, we have already considered. They can be with one wire (the signal is sent directly to the computer) or with two (the second is responsible for grounding the case). It is worth paying a little attention to the other two categories, as they have a more complex structure.

Two-point heated

In two-point modifications with heating, there will be three or four wires. In the first case, this will be a plus and minus for heating the spiral, and the third (black) signal. The second type of sensors has the same circuit, with the exception of the fourth wire. This is the grounding element.

What is a lambda probe in a car and how to check it

Broadband

Broadband probes have the most complex of all the connections to the car system. It has five wires. Each manufacturer uses its own marking to indicate which one is responsible for what. Most often black is signal, and gray is grounding.

What is a lambda probe in a car and how to check it

The other two cables are heating power. Another wire is the injection signal wire. This element controls the air concentration in the sensor. Pumping occurs due to a change in the current strength in this element.

Symptoms of a Lambda Probe

The very first sign of a faulty sensor is an increase in fuel consumption (while the operating conditions of the machine do not change). In this case, a decrease in dynamic characteristics will be observed. However, this parameter should not be the only measure.

Here are some more “symptoms” of a failed probe:

  • Increased concentration of CO. This parameter is measured by a special device.
  • On the dashboard, the engine's CHECK signal lights up. But in this case, you should contact the service. Warning may not apply to this sensor.

The oxygen sensor fails for the following reasons:

  • Natural wear.
  • Antifreeze hit him.
  • Improperly cleaned the case.
  • Poor fuel (high lead content).
  • Overheated.

Lambda probe verification methods

To check the serviceability of the lambda probe, a multimeter is enough. The work is carried out in the following order:

  • An external examination is carried out. Soot on its body indicates that it could burn out.
  • The sensor is disconnected from the electric circuit, the engine starts.
  • The tip must be heated to operating temperature. To do this, keep the engine speed within 2-3 thousand revolutions.
  • The multimeter contacts are connected to the sensor wires. The positive terminal of the device is on the signal wire (black). Negative - to ground (gray wire, if not, then just to the car body).
  • If the sensor is serviceable, then the multimeter will fluctuate within 0,2-0,8 V. A faulty lambda probe will give readings from 0,3 to 0,7 V. If the indicator is stable on the screen, this means that the sensor is not functioning .
What is a lambda probe in a car and how to check it

Replacement and repair of a lambda probe

What to do if the sensor fails? It must be replaced. It is not being repaired. True, some masters use tricks or turn off the sensor. However, such methods are fraught with malfunctions of the catalyst and a decrease in the efficiency of the internal combustion engine.

Change the sensor to a similar one. The fact is that the ECU adapts to the parameters of a particular device. If you install another modification, there is a high probability of giving the wrong signals. This can lead to various unpleasant consequences, including a quick failure of the catalyst.

What is a lambda probe in a car and how to check it

The lambda probe must be replaced with a cold motor. When buying a new oxygen sensor, it is extremely important to make sure that the original was purchased, and not an analogue suitable for this car. The malfunction will not immediately be noticeable, but subsequently the device will stop working again.

The procedure for installing a new sensor is very simple:

  • The wires from the old probe are disconnected.
  • The defective sensor is twisted.
  • A new one is being screwed in its place.
  • Wires are worn in accordance with the marking.

When replacing the oxygen sensor, you must be careful so as not to disrupt the thread on it or in the exhaust pipe. After replacement, the engine is started and the device is checked for operability (using a multimeter, as described above).

As you can see, the efficiency of the car engine depends on the parameters coming from the lambda probe to the computer. The importance of the sensor increases if the exhaust system is equipped with a catalytic converter.

Questions and answers:

Where are the lambda probes? The sensor is screwed into the exhaust system as close to the catalyst as possible. Modern cars use two lambda probes (one in front of the catalyst and the other behind it).

What is the function of the lambda probe sensor? This sensor monitors the composition of the exhaust gas. Based on its signals, the control unit adjusts the composition of the air-fuel mixture.

One comment

  • Tristan

    Thank you for the information, it was really detailed!
    The only thing missing in terms of buying a lambda probe after the catalytic converter is whether it is called something special.
    Eg. I read diagnostic probe about the one who sits after cat. but not many people write their names

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