Inspection Methods
1)Oxygen Sensor
①Check whether there is damage or dent on the surface of oxygen sensor,and if yes,the sensor foult may be caused by mechanical damage;Put the outer gasket ring of oxygen sensor by hand close to the ear and wave it gently,and if there is abnormal noise,the inner ceramic element may be damaged by temperature shock or external mechanical force.
②Observe the color of the oxygen sensor head and if there appears rufous(reddish brown)or white color,then the oxygen sensor may be“poisoned”by the quality problem of fuel.
③Use the universal meter to measure the resistance between the two white wire harness(plug structure is shown in Fig.4.17)and the value is around 7-11Ωunder normal temperature.
Fig.4.17 Plug Structure of Oxygen Sensor
④Under idling condition,when the working temperature of oxygen sensor reaches 350 °C(about 3 min),use the universal meter to check the voltage of front oxygen sensor signal and the voltage value should fluctuate between 0.1-0.9 V.Use the oscilloscope to check the signal and the reference wave shape is shown in Fig.4.18.The signal frequency varies with the rotation speed of the engine;and at the medium rotation speed,times of jumping changes of signal wave shape in 10 s shouldn’t be less than 8.The voltage of rear oxygen sensor signal is stable,usually around 0.6 V.
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Fig.4.18 Signal Wave Shape of Front Oxygen Sensor
⑤Under idling condition,check the heating signal wire of the sensor and there is a continuous jumping change of voltage from low to high and test lamp flickers when it is used to check.
2)Carbon Canister Purge Solenoid(Fig.4.19)
①Use the universal meter to measure the resistance of carbon canister purge solenoid coil and the reference resistance under normal temperature is(26±4) Ω.
②Inspect the purge solenoid:dismantle the carbon canister purge solenoid and blow air inside purge solenoid and at the moment,there should be no air leakage;apply the voltage of 12 V on the both wire terminal of carbon canister control valve and then blow air inside.At this moment,the air should flow through purge solenoid.
③Use the element test function of the diagnostic unit and adjust the scour rate of purge solenoid under the idling condition,and then there should be fluctuations in the vehicle’s rotation speed.
Fig.4.19 Action Test of Carbon Canister Purge Solenoid