A negative pump current is the result of this. This pump current is evaluated by the control unit, providing the air ratio and thus information about the air-fuel ratio. Since the introduction of the EOBD, the function of the catalytic converter must also be monitored. An additional lambda sensor is installed behind the catalytic converter for this. This is used to determine the ability of the catalytic converter to store oxygen. The function of the probe downstream of the catalytic converter is the same as the upstream probe.
The amplitudes of the lambda sensors are compared in the control unit. The voltage amplitudes of the downstream probe are very small due to the ability of the catalytic converter to store oxygen.
The lower the storage capacity of the catalytic converter, the higher the voltage amplitudes of the downstream probe due to the increased oxygen content. The heights of the amplitudes at the downstream probe are dependent on the actual storage capacity of the catalytic converter, which varies depending on the load and speed.
The load condition and speed are therefore taken into consideration when comparing the probe amplitudes. If the voltage amplitudes of both probes are still roughly the same, the storage capacity of the catalytic converter has been reached, e.
There are a range of typical lambda sensor faults that occur frequently. The following list shows the causes behind diagnosed faults:. Vehicles that are equipped with self-diagnostics can detect faults occurring in the control circuit and store them in the fault memory. This is usually displayed through the engine indicator lamp. The fault memory can then be read out with a diagnostic unit for fault diagnostics. However, older systems are not able to determine whether this fault relates to a defective component or e.
In this case, further tests must be carried out by the mechanic. As part of the EOBD, the lambda sensor monitoring has been expanded to include the following points:. In order to diagnose the lambda sensor signals, the control unit uses the form of the signal frequency. Response time: Probe reacts too slowly to mixture change and no longer displays the status at the right time. If the probe voltage exceeds the control threshold, the time measurement between the positive and negative flank begins.
If the probe voltage falls short of the control threshold, the time measurement stops. The time period between the start and end of the time measurement is measured by a counter. If the probe is severely aged or contaminated, e. The probe signal is compared with a stored signal pattern. A slow probe is detected as a fault, e.
As a basic principle, a visual inspection should be carried out before each check to ensure that there is no damage to the cable or connector. The exhaust system must not have any leaks. It is recommended to use an adapter cable to connect the measuring device. It must also be ensured that the lambda control is not active during some operating states, e. The test is carried out in the same way as the prescribed exhaust emissions test. With the engine is at operating temperature, false air is connected as a disturbance variable by removing a hose.
Through the changing exhaust gas composition, the lambda value that is calculated and displayed by the exhaust tester also changes. The mixture formation system must detect this from a certain value and adjust it within a certain time 60 seconds, as in the exhaust emissions test. If the disturbance variable is removed, the lambda value must be reduced to the original value. As a basic principle, the specifications for disturbance variable connection and the lambda values of the manufacturer should be observed.
However, this test can only determine whether the lambda control is working. An electrical test is not possible. Multimeters with a low internal resistance mostly in analog devices overload the lambda sensor signal and may cause it to break down. There are two parts in Lambda Sensor — Sensor that gets heated and the heating sensor. The heating sensor helps the Lambda sensor in reaching its operating temperature. When the engine reaches the right temperature, the sensor starts measuring the unburnt oxygen present in the exhaust gases.
This output is sent to the computer unit where it calculates the air-fuel ratio and checks the look-up table to optimize this air-fuel ratio. Based on this information, a calculated amount of fuel required by the engine to burn at a stoichiometric ratio is released, ensuring complete combustion.
In automobiles two Lambda sensors are used — one installed before the catalyst converter, which controls the system and the other installed behind the catalyst converter, to make sure the former one is working properly. The social media platform linked to the respective social plugin may use information in regards to your website visits and assign this data to your personal social media account, observe your browsing habits or create and process personal profiles.
You may opt-out of this process at any time, for more information please check our Privacy Policy. The sensor measures the percentage of unburned oxygen to see if there is too much the mixture is too lean or too little the mixture is too rich. The results are sent to the Electronic Engine Control Unit ECU so that the amount of fuel entering the engine can be adjusted for an optimum mixture.
This is constantly changing depending on a number of factors, including the engine load e. In the market there are three types of lambda sensors, the oldest ones and most common in the market are the zirconium oxide lambda sensors.
This type exist in different configuration one, two, three or four wires , depending if the sensor is preheated or not. The second type is the titanium oxide lambda sensor, also available in four different types see the picture , this type is easy to identify because the diameter of the threat is smaller than the zirconium oxide as a visual tip, these sensors have yellow and red wires.
The wide band lambda sensor is the most common one in the new vehicles equipped with two lambda sensors per catalytic converter. The lambda sensor is used to regulate the fuel mixture, with the ECU responding to measurements from the sensor to determine the amount of fuel needed.
This means the fuel mixture will be constantly fluctuating between rich to lean, allowing the catalytic converter to operate at peak efficiency, while balancing the overall mixture to minimize emissions. If the lambda sensor or the wires are damaged or worn, the vehicle will be circulationg in rich mixture constantly, increasing fuel consuption and putting in risk other elements of the emission control system as catalytic converters.
The sensors are designed to work within government exhaust gas legislation. Due to the role they play in the operation of your car, they are also widely known as oxygen sensors or O2 sensors. When your car burns petrol or diesel, it mixes it with air to provide the most efficient operation of your engine. This ratio of air to fuel is known as the stoichiometric ratio.
Or, and much easier to pronounce, the lambda ratio. With fuel that runs rich, there is excess, unburned fuel. A lean fuel mix tends to produce more nitrogen-oxide pollutants. It can also cause poor engine performance and possible engine damage. In modern cars, there are often 2 sensors. The first is directly after the engine and before the catalytic converter. The second is placed after the catalytic converter to monitor the overall operation. It also checks that your cat is doing is its job correctly.
Your lambda sensor converts the amount of oxygen present in your exhaust into an electric signal and sends the signal to the computer that controls your engine operation.
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