Faults of the Oxygen Sensor
● Oxygen sensor poisoning
● Carbon deposit
● Oxygen Sensor Ceramics cracked
● Heater resistance wires burnt out
● Oxygen Sensor internal circuits broken
off Inspection methods of faults
● Checking of the oxygen sensor heater resistance
Unplug the oxygen sensor wiring harness plug, and measure
the resistance with a multimeter between the oxygen
sensor heater terminals connected column and bond strap
connected column, its standard resistance is 4-40Ω.
If not meet standards, you should replace the oxygen
● Measurement of the oxygen sensor feedback
When measuring oxygen sensor feedback voltage, you should
unplug the oxygen sensor wiring harness plug. First,
collate electric circuit chart, and extract a thin wire
from output terminal of the oxygen sensor feedback voltage.
Then plug the wiring harness plug, and measure the feedback
voltage from the outgoing line in the engine running.
When detecting the oxygen sensor feedback voltage, you
would best to use low-range (typically 2V) and high-impedance
(R＞10MΩ) pointer-type multimeters. Specific detection
methods are as follows:
1) Heat the car's engine to a normal operating temperature
(or start running for 2min at a speed of 2500r/min)
2) Put the negative pen-shape metre of voltage profile
multimeters to contact the E1 within failure detection
socket or the battery negative, and the positive pen-shape
metre to contact the OX1 or OX2 jack within failure
detection socket, or receive the signal output line
of oxygen sensor wiring harness plug.
3) Allow the engine to remain running at a speed of
around 2500 r/min, and at the same time check whether
the voltmeter pointer could swing back and forth between
0-1V, and note the swing number of voltmeter pointer
within 10s. Under normal circumstances, with the ongoing
of feedback control, oxygen sensor feedback voltage
will be 0.45V changing up and down, the change number
of feedback voltage should not less than 8 times. If
less than 8 times, it shows that the oxygen sensor or
feedback control system is not working properly. The
reason may be the oxygen sensor surface carbon deposition,
making lower sensitivity. This should allow the engine
to run at a speed of 2500 r/min for 2min, to clear the
carbon deposition of oxygen sensor, and then check the
feedback voltage. If after clearing the carbon deposition,
the change of voltmeter pointer is still slow, it shows
that the oxygen sensor is broken or the computer feedback
control circuit is defective.
4) Check the oxygen sensor whether damage
Unplug the oxygen sensor wiring harness plug, so that
the oxygen sensor is no longer connected to the computer,
and the feedback control system is in a state of open-loop
control. Put the positive pen-shape metre of voltage
profile multimeter to directly connect with the feedback
voltage output terminal of oxygen sensor, and the negative
pen-shape metre have a good put up iron. Measure the
feedback voltage in the course of engine running. First
disengage the crankcase forced ventilation tube which
connected to the intake manifold or other vacuum hose,
to artificially form dilute mixture gas, and also notice
the voltmeter, its pointer readings should decline.
Then connect the disengaged pipe up, and disconnect
the water temperature sensor connector, and substitute
with a 4-8 KΩ resistance to a water temperature sensor,
to artificially form rich mixture gas, and also notice
the voltmeter, its pointer readings should be increase.
It also can use a method of suddenly trample or loose
accelerator pedal to change the concentration of the
mixture. When you suddenly trample the accelerator pedal,
the mixture gas become thicken, and the feedback voltage
should be increased; when you suddenly loose the accelerator
pedal, the mixture gas become thinning, and the feedback
voltage should decline. If the oxygen sensor feedback
voltage has no above changes, shows that the oxygen
sensor is damaged.
5) Check the color appearance of oxygen sensor
Remove the oxygen sensor from the exhaust pipe, Check
the venthole of sensor enclosure whether be plug and
the ceramic core whether be damaged. If damaged, you
should to replace the oxygen sensor.
We can also judge faults by observing the top color
of oxygen sensor, such as:
① Light gray top: This is the normal color of oxygen
② White top: It caused by the silicon contamination,
this moment you must replace the oxygen sensor.
③ Brown top: It caused by the lead contamination, if
serious, must also replace the oxygen sensor.
Black top: It due to the carbon deposit, after excluding
the fault of engine carbon deposit, general it can automatically
clear the carbon deposit of oxygen sensor.