What you need to know about a narrowband lambda probe with a ceramic coating?

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02/02/2021
What you need to know about a narrowband lambda probe with a ceramic coating?

A sensitive element made of zirconium dioxide is installed under the protective metal cap of the lambda probe. Such ceramics are an electrolyte (ie, conductive), but for gases it is completely impermeable.

 

The sensitive element has a contact coating on the outside and inside, it is connected to the signal wires. The operating temperature of the ceramic-coated lambda probe is about 350 degrees Celsius. Early versions of lambda probes did not have forced heating, but were heated by exhaust gases. Later versions have a built-in heater that brings them to operating temperature fairly quickly.

 

The inner part of the ceramic is in contact with the air, and the outer part - with the exhaust gases. The difference in the concentration of oxygen molecules in the exhaust gases and atmospheric air (inside and outside the sensor) causes the movement of oxygen ions from the region of high oxygen content to the region of low content. The ions are moved through a ceramic element, which is a solid electrolyte.

 

Actually, the difference in the amount of oxygen outside and inside the sensor and forms a signal voltage. 0.45 Volts is one (ie, lambda is one). "Poor" fuel-air mixture generates a voltage of 0.1 volts, "rich" generates 0.9 volts. This is how a narrowband oxygen sensor works.

 

Lambda probe - DRIVE2

 

One to four wires can be connected to the narrowband sensor (3-4 wires indicate the presence of heating). Two white wires supply the lambda probe heater, on the black wire - a signal to the ECU, on the gray - ground. There may also be three wires without ground, and the ground in this case is connected to the housing.

 

To diagnose a narrowband sensor, you need to take an oscillogram or look at it through diagnostic software. The signal must change quickly - at least once a second. The voltage should be in the range from 0.1 to 0.9 volts. If the signal voltage is lower and changes infrequently, this indicates a fault in the lambda probe. The sensor must also actively respond to changes in the composition of the fuel-air mixture.

 

By the way, the mixture can be changed from the outside: for "enrichment" to inject propane into the starting valve (the signal from the sensor should jump to 0.9 Volts), and for "depletion" to create "suction" of air, removing a vacuum tube (signal voltage decreases to 0 , 1 Volt). It can be made even simpler: open and close the throttle valve by pressing and releasing the accelerator pedal.

 

Then the indicators must change quickly and stabilize. This method is convenient if the exhaust system of the engine has two catalysts and a pair of "upper" lambda probes. Preferably this scheme is used on V-shaped and 6-cylinder engines.

 

The reaction rate of the two lambda probes can be compared. Preferably, the faulty one will react more slowly.

 

The heating element of the lambda probe is checked simply. To begin with, make sure that the battery is powered by 9 to 12 volts (depending on the car). Then measure the resistance of the heater: in good condition it should be 2.3 - 4.4 ohms at 25 degrees Celsius. If the sensor is removed, you can heal it from the battery - in a few minutes the lambda probe should heat up to 350 degrees Celsius.