Page 249 - Foton Workshop Manual - Aumark (BJ1099)

ENGINE CONTROL SYSTEM - FRONT OXYGEN SENSOR 11-23
FRONT OXYGEN SENSOR

1. Principle of Work
The sensing element of oxygen sensor is a kind of ceramic tube with hole. The
outside of tube wall is surrounded by engine exhaust emission, while the inner side
connects to the atmosphere. The sensing ceramic wall is a kind of solid electrolyte
with electric heating tube inside. The work of oxygen sensor is realized through
transforming the oxygen ion concentration difference inside and outside the sensing
ceramic tube into the voltage signal output. The sensing ceramic tube will have 11
the property of solid electrolyte when its temperature reaches 350 ℃ . Due to the
particularity of its texture, the oxygen ion can go through the ceramic tube freely.
Utilizing this feature, the concentration difference is transformed into potential
difference, thereby forming electrical signal output. If the mixed fas is thicker, The
oxygen ion concentration difference inside and outside the ceramic tube will be
higher, so is the potential difference, and a large amount of oxygen ions will move
from inside to outside, leading to a higher output voltage (near 800-1000mV). If the
mixed fas is in low concentration, the oxygen ion concentration difference inside
and outside the ceramic tube will be lower, so is the potential difference, and only
a small amount of oxygen ions will move from inside to outside, leading to a lower
output voltage (near 100mV).
2. Function and installation
It is used in the feedback system of electronic control fuel injection device to realize
the closed-loop control and improve ECU's control accuracy for air-fuel ratio. It is
installed in the exhaust pipe (before three-way catalyst) to determine the oxygen
content in exhaust gas and whether gasoline and air are thoroughly burned, so as
to ensure that three-way catalytic converter has a maximum conversion efficiency to
HC, CO and NOX in exhaust gas.
3. Fault phenomenon and judgment method
(a). Fault phenomenon: Poor idling, poor acceleration, tail gas exceeding standard and
too large fuel consumption, etc..
(b). General causes for faults:
• Wet moisture enters into the sensor. Temperature changes sharply. The probe
breaks;
• Oxygen sensor "poisoning". (such as Pb, S, Br and Si, etc.)
(c). Precautions for maintenance:
• Using cleaning fluid, oily liquid or volatile solid on the sensor during maintenance
is prohibited.

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