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Everything you need to know about lambda probes

Everything you need to know about lambda probes 1
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Everything you need to know about lambda probes

Everything you need to know about lambda probes

The lambda probe is one of the elements of the power supply system for injection vehicles, which in our operating conditions can create problems. How to avoid them?

Greek lambda in the automotive industry denotes the coefficient of excess air in the air-fuel mixture. From here came the name of the sensor that measures this coefficient, or rather, the residual oxygen (O2) in the exhaust gases (another name is the oxygen sensor). The purpose of the sensor is to provide the engine ECU with information to determine the nature of the fuel combustion. 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). To ensure such precise control of the composition of the fuel-air mixture is possible only with the help of power systems with electronic fuel injection. The lambda probe in these systems acts as a controller in the exhaust tract.

Lambda probe: causes and symptoms of breakdowns Malfunctions or even a failure of the lambda probe can occur due to: interruptions in the electrical circuits; short circuits; contamination with gasoline combustion products with a high content of octane enhancing additives; thermal overload due to interruptions in the ignition; mechanical damage (for example, when driving on the road). The poor condition of the oil scraper rings, the ingress of antifreeze into the cylinders and exhaust pipes, and the enriched fuel-air mixture greatly reduce the life of the lambda probe. With a faulty lambda probe, the CO content in the exhaust increases from 0.1–0.3% to 3–7%. It is difficult to reduce its value in most old motors without replacing the sensor, since the range of the potentiometer mixture quality regulator may not be enough. 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.

Symptoms of a Lambda Sensor:

  • Deterioration of throttle response (acceleration dynamics)
  • Unstable idling
  • Increased fuel consumption
  • Increased exhaust toxicity

Sensor replacement intervals:

  • for the unheated – every 50,000-80000 km
  • for heated – every 100,000 km
  • for planar – every 160,000 km

Lambda probe: treatment of malfunction

Technology for repairing faulty lambda probes does not exist – in case of 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 of soot on the sensitive element under the protective cap. If the plaque is removed, the performance of the “lambda” is restored. The sensor’s sensitive element can be cleaned by washing it in phosphoric acid, which in 10–20 minutes corrodes pollution without destroying the electrodes with rare-earth metals. It is more efficient to clean the lambda probe after removing the protective cap on the lathe and washing with a thin brush. But it is advisable to do this if it is possible to fix the cap using argon welding. After washing, rinse the sensor with water and dry it. If washing does not help, then the lambda needs to be changed. The cost of washing is much less than the cost of a new lambda probe (from 300 UAH.). You can replace an unheated sensor with a heated one (but not vice versa!). If the connectors are incompatible, lay the missing heating circuit yourself, and use universal automobile contacts instead of the connector. Why change the lambda probe in time: the new lambda probe saves up to 15% of fuel, the exhaust gas toxicity is not reduced, the catalyst resource is not reduced, the dynamic characteristics of the engine are unchanged.

Lambda probe: diagnosis

An effective measurement of the residual oxygen in the exhaust gases of the lambda probe provides after it is heated to a temperature of 300-400 ° C. Only in such conditions does the zirconium electrolyte acquire conductivity, and the difference in the amount of atmospheric oxygen and oxygen in the exhaust pipe leads to the appearance of an output voltage on the electrodes of the lambda probe. Therefore, the signal from the lambda probe is checked with the engine turned on and warm. An oscilloscope is better suited for measurement than a multimeter, because with its help the waveform and frequency of the signal are most accurately estimated. Then the resistance of the sensor heater is measured (with the plug disconnected), which is at room temperature from 2 to 14 Ohms (according to the manufacturer’s requirements). Next, the voltage supplied to the heater is checked: with the ignition on and the probe connector connected, it should be at least 10.5 V. If this value is lower, carefully check the battery voltage, cables and connections. Lambda probe: mounting details

If the lambda probe is reused, the thread must be treated with a special mounting paste. In this case, the paste should not be allowed to get on the protective tube, as this may lead to malfunction of the sensor. New lambda probes from leading manufacturers are pre-treated with paste. Follow the manufacturer’s specified tightening torque, usually between 40 and 60 Nm. Lambda probes must be handled with care to avoid mechanical damage (e.g. due to a fall). Since the sensors suck in external (reference, for comparison) air through the connector, it cannot be treated with a contact spray or grease. When flushing the engine and underbody, the lambda probe connector must be carefully insulated..

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