When the powertrain control module receives a low voltage lean signal, it compensates by increasing the amount of fuel in the mixture. When the powertrain control module receives a high voltage rich signal, it leans the mixture by reducing the amount of fuel it adds to the mixture.
This closed-loop operation results in a constant flip-flop between rich and lean, which allows the catalytic converter to minimize emissions by keeping the overall average ratio of the fuel mixture in proper balance. However, when a cold engine is started, or if an oxygen sensor fails, the powertrain control module enters into open-loop operation.
In open-loop operation, the powertrain control module does not receive a signal from the oxygen sensor and orders a fixed rich fuel mixture. Open-loop operation results in increased fuel consumption and emissions. Many newer oxygen sensors contain heating elements to help them get to operating temperature quickly in order to minimize the amount of time spent in open-loop operation.
Oxygen sensor 2 is the downstream oxygen sensor in relationship to the catalytic converter. It measures the air-fuel ratio coming out of the catalytic converter to ensure the catalytic converter is functioning properly. The catalytic converter works to maintain the stoichiometric air-fuel ratio Therefore, the downstream oxygen sensor sensor 2 should produce a steady voltage of approximately 0.
Step by step guide on how an automotive oxygen sensor works, this article pertains to most vehicles. Step 1 — An oxygen sensor is an electronic component that is designed to measure levels of oxygen in an automotive engine exhaust system. Step 2 — Typically, the oxygen sensor is mounted to the exhaust system tube or on the side of a catalytic converter, with the sensor part inside the tube.
This measures the oxygen mixture by generating a small amount of electricity due to the difference in atmosphere, oxygen and carbon dioxide. The computer PCM monitors this voltage and adjusts fuel delivery accordingly. Oxygen sensors can usually be found in the exhaust pipe near the engine primary sensor although sometimes they are mounted in the exhaust manifold itself where the exhaust pipe connects.
Sensors found after or on the catalytic converter is the secondary unit. Oxygen sensors do this through a chemical reaction inside the sensor itself; in this article, we will explain the evolution and application of this very important piece of the fuel injection puzzle. Oxygen sensors work through a chemical reaction.
The core or element of the sensor is Zirconia ceramic with a thin layer of platinum. Since these materials are reactive and are applied as layers they will eventually wear out reducing their efficiency. Step 4 — The voltage created by the sensor is then relayed to the computer where it will compare it with other live information to make the necessary mixture and timing adjustments.
For the diagnosys of the wide band lambda sensors the use of a scan tool or oscilloscope is needed. Use a specialized socket to facilitate the removal of the lambda sensor. Check for the right application at the catalogue, similar applications may have different reaction time, not being equivalents. Use grease around the thread on the new sensor to make it easier to install the sensor now and remove it again at a later date. The sensor can be threaded into place by hand and tightened with the special socket to its right torque specified at the service manual of the vehicle.
Take a step closer to the action, and watch a Garage Gurus expert show you exactly how to check, remove and replace a lambda sensor. For informational purposes only. We are not liable for any damages resulting from your reliance on this content. Please review and accept our Privacy Policy before signing up for the newsletter. How to check and replace a lambda sensor? Message Regarding Your Privacy. I accept Submit Submit. 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. One of the quickest and easiest tests is to measure with the four-gas emission analyser. 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.
Due to the quickly alternating voltage, the signal is best depicted with an analog device. The multimeter is connected parallel to the signal line black cable, see circuit diagram of the lambda sensor. The measuring range of the multimeter is set to 1 V or 2 V. After the engine is started, a value between 0. If the operating temperature of the engine or lambda sensor is reached, the fixed voltage begins to alternate between 0. In order to achieve flawless measuring results, the engine should be kept at a speed of approx.
This ensures that the operating temperature of the probe is reached, even in systems with an unheated lambda sensor. If the exhaust gas temperature is not sufficient in idle mode, there is a risk that the unheated probe cools down and a signal is no longer generated. The lambda sensor signal is best depicted using the oscilloscope. As for the measurement with the multimeter, a basic prerequisite is that the engine or lambda sensor must be at operating temperature.
The oscilloscope is connected to the signal line. The measuring range to be set is dependent on the oscilloscope used. If the device has automatic signal detection, this should be used. For manual adjustment, set a voltage range of 1 — 5 V and a time setting of 1 — 2 seconds. The alternating voltage appears on the display in sinusoidal form. The following parameters can be evaluated at this signal:. When it comes to replacing your sensor , here are a few tips for a clean and correct installation:.
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Enter your details to see exact price Your postcode. Your registration number. About Fixter Fixter is revolutionising the car maintenance industry, one repair at a time. Category: Car advice 13th November Tags: catalytic converter emissions exhaust exhaust systems lambda sensor. Previous Previous post: What is Cat D damage on a car?
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