Maintenance Manual for Chery·Windcloud Marelli EFI System
5. Oxygen Sensor
Purpose: this sensor is designed to provide
the information that if there is surplus
oxygen after full combustion of fuel, which
is injected into engine cylinder in the intake
air. ECU, when applying this information,
can carry out fuel quantitative closed-loop
control so as to achieve utmost conversion
and purification of the three major toxic
elements in the engine exhaust with the
application of three-way catalytic converter.
Note that installation of three-way catalytic
converter will costs some of engine power.
Composition and principle: the nature of
oxygen sensor is atomic battery, while
sensing element of oxygen sensor is a
porous ceramic pipe, the outer side of pipe
wall is surrounded by engine exhaust, while
inner side vents to atmosphere. According to
inside and outside oxygen concentration
difference, sensor figures out indirectly if
the fuel injection is in excessive quantity,
and then transfers the information to ECU,
and the ECU controls the injection again.
The working voltage of oxygen sensor
fluctuates between 0.1-0.9V, 5-8 variations
in 10 seconds is required; if lower than such
frequency value, it shows that the sensor is
aged, damaged or poisoned, and needs
replacement. The said sensor is
unrepairable.
Failure diagnosis: ECU monitors on
various sensors, actuators, power
amplification circuits and sensing circuits. In
case any of the following situations occurs,
failure mark of the oxygen sensor is set.
Accumulator voltage is unreliable
Manifold absolute pressure signal is
unreliable
Engine coolant temperature signal is
unreliable.
Injector driver stage failure
After oxygen sensor failure mark is set, fuel
quantification closed-loop control is shut
down, and the primitive fuel injection time
stored in ECU is used to carry out fuel
quantification.
Installation hints: the tightening torque of
oxygen sensor is 50-60Nm, a layer of rust
preventive oil shall be applied on mounting
screw thread of oxygen sensor after
replacing so as to prevent from incapable
removal in case of rust.
Troubleshooting: mainly check if the plug
connection of several wires on the sensor is
in good condition, and if there is short
circuit or open circuit.
Generally, sensor damage is caused by
plumbum and phosphorus poisoning, so
pay attention to fuel quality, meanwhile
excessive consumption of engine oil is
liable to result in sensor failure.
Main relay
Oxygen
sensor
Circuit diagram of oxygen sensor
Oxygen sensor has a cable, the other end of
which is electric connection. The outside of
sensor is wrapped with asbestos fireproof
covering.
There are 4 pins on the joint:
1# connecting with sensor signal anode
(ECU 20#);
2# connecting with sensor signal cathode
(ECU 9#);
3# connecting with power supply and main
relay;
4# connecting with heating control (ECU
28#).
Interior structure of oxygen sensor
5
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