- Purpose Greek lambda in the automotive industry refers to the coefficient of excess air in the air-fuel...
- Lambda probe: malfunction treatment
- Lambda probe: diagnosis
- Lambda probe: installation details
Purpose
Greek lambda in the automotive industry refers to the coefficient of excess air in the air-fuel mixture. Hence the name of the sensor, which measures this coefficient, or rather the residual oxygen (O2) in the exhaust gases (also called oxygen sensor). The purpose of the sensor is to provide the engine ECU with information to determine the nature of the combustion of the fuel. This is necessary to create normal operating conditions for the catalytic converter. The fact is that the “window” of effective catalyst operation is very narrow, when 14.6–14.8 parts of air and 1 part of fuel are burned in cylinders (when such a mixture is burned, lambda = 1 ± 0.01). It is possible to ensure such precise regulation of the composition of the fuel-air mixture only with the help of power supply systems with electronic fuel injection. Lambda probe in these systems performs the function of the controller in the exhaust tract.
Lambda probe: causes and symptoms of breakdowns
A malfunction or even failure of a lambda probe may occur due to:
The lambda probe service life is greatly reduced by the poor condition of the oil wiper rings, the ingress of antifreeze to the cylinders and exhaust pipes, and the enriched fuel-air mixture.
With a malfunctioning lambda probe, the CO content in the exhaust increases from 0.1–0.3% to 3–7%. Reducing its value in most old motors without replacing the sensor is difficult, since the potentiometer's mixture quality regulator may not have enough power reserve. In cars with two lambda probes in the event of a second sensor failure, it is impossible to achieve normal engine operation without serious interference with the electronics.
Lambda probe: malfunction treatment
There is no technology for repairing defective lambda probes - in case of a breakdown, they must be replaced. However, our "Uncle Vasya" still developed a method for restoring these sensors, but it is not effective in all cases. Most often, it stops working due to deposits on the sensitive element under the protective cap. If the plaque is removed, the performance of the lambda is restored. The sensor's sensor can be cleaned by rinsing it in phosphoric acid, which in 10–20 minutes eats away pollution without destroying electrodes with rare-earth metals. It is more efficient to clean the lambda probe after removing the protective cap on a lathe and washing with a thin brush. But it is advisable to do this if it is possible to fasten the cap using argon welding. After washing the sensor should be rinsed with water and dried. If washing does not help, then the lambda needs to be changed. The cost of washing is significantly less than the cost of a new lambda probe (from UAH 300). You can replace an unheated sensor with a heated one (but not vice versa!). If the connectors are incompatible, run the missing electrical circuit independently, and use universal automotive contacts instead of the connector.
Lambda probe: diagnosis
Bosch experts recommend checking the lambda sensor and the fuel mixture control system every 30 thousand kilometers.
Effective measurement of residual oxygen in the exhaust gases lambda probe provides, after its heating to a temperature of 300-400 ° C. Only in such conditions the zirconium electrolyte acquires conductivity, and the difference in the amount of atmospheric oxygen and oxygen in the exhaust pipe leads to the output voltage on the lambda probe electrodes. Therefore, the lambda probe signal is checked with the engine turned on and warmed up. An oscilloscope is better suited to measurement than a multimeter, because with its help the signal shape and frequency are most accurately estimated.
Then, the resistance of the sensor heater (with the plug disconnected), measured at room temperature from 2 to 14 ohms (as required by the manufacturer), is measured. Next, the voltage supplied to the heater is checked: when the ignition is on and the probe connector is connected, it should be at least 10.5 V. If this value is lower, you should carefully check the battery voltage, cables and connections.
Lambda probe: installation details
Opinion 
Vadim Dolgiy
Technical Consultant, Robert Bosch Ltd.
When the lambda probe fails, the question arises of where to buy a new one. This is not a problem, since universal lambda probes have been created for installation on any car. They differ from “normal” only in the way of connection. To connect the universal lambda probe, Bosch has developed a special adapter that connects to the standard wiring of the plug of the old probe. The adapter provides an accurate and stable signal, is waterproof, is not affected by temperature drops and vibrations, and ensures that fresh air reaches the measuring element.
Yury Datsyk
Photo Bosch, GM
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