When
in the automotive troubleshooting work, for the high frequency of failure, also known as the common faults, we after the completion of repair work, only need to remember that diagnostic results, next time you encounter the same fault on direct repair or replace corresponding parts in order to achieve rapid problem resolution. For low frequency of failure, or cause of the failure is not common, we need to remember repair methods and procedures, and to draw lessons which, at a later date in order to avoid detours or consuming too long.
Failure phenomenon: a 2006 model 2.5 L FAW Toyota Crown sedan, equipped with a V6 engine. According to reflect the user, the engine fault light on the vehicle instrument lighting.
Check Analysis: fault diagnostic read fault code P0136 (1, row 2 of the oxygen sensor failure), the oxygen sensor circuit inspection No abnormal changes slowly oxygen sensor values observed in the data stream, so the replacement Oxygen Sensor. And running for some time, engine failure light up again, still read the fault code P0136.
FIG 1
The car is equipped with an engine air-fuel ratio sensor (FIG. 1) and an oxygen sensor. When the combustible gas mixture after the lean air-fuel ratio sensor generates a current direction is positive, the current input to the internal circuit detects an engine control unit, a voltage corresponding to greater than 3.3 V, the lean burn the air-fuel ratio read out diagnostic The higher the value of the sensor voltage. When the combustible gas mixture rich air-fuel ratio sensor generates a negative current direction, the current input to the engine control unit detects the internal circuit, a voltage corresponding to less than 3.3 V, the rich mixture in the diagnostic readout empty the lower fuel ratio sensor voltage value. When the engine proper mixture gas air-fuel ratio sensor current is zero, the diagnostic value of the air-fuel ratio sensor read is always 3.3 V. When rich air-fuel mixture, the oxygen sensor corresponding to a voltage of 0.45 ~ 1 V; when the lean air-fuel mixture, the oxygen sensor corresponding to 0 ~ 0.45 V voltage. By varying the voltage value of the oxygen sensor, the engine control unit can be informed of the operation of the three-way catalyst.
FIG. 2
For the car engine, the engine cylinders 1, 3 and 5 cylinders sharing a three-cylinderCatalytic converters, the front three-way catalyst equipped with an air-fuel ratio sensor, called the air-fuel ratio sensor 1, row 1, the three-way catalyst equipped with an oxygen sensor, called the oxygen sensor 1, row 2; 2-cylinder, 4-cylinder, and a six-cylinder common three-way catalyst, referred to the corresponding sensor 2, row 1, row 2 and the air-fuel ratio sensor 2 of the oxygen sensor. After a review of the data stream of the engine, the accelerator pedal is depressed for some time, the value 2, row 2 of the oxygen sensor will change from 0 to 1 V, but the value of the oxygen sensor 1, row 2 (FIG. 2) is always around 0 V. The two interchangeable oxygen sensor, there is no change (Table 1).
Table 1
1 row of maintenance personnel suspected fault catalytic converters, resulting in a value of 1, row 2 of the oxygen sensor does not change. Dismantling found inside a row of three-way catalyst has been sintered, so the replacement of a row of three-way catalyst. Car and running for some time, engine failure light up again, still read the fault code P0136. Using long fault diagnostic engine data stream for each observation condition, the ignition switch while the engine is not running, air-fuel ratio sensor 1, row 1 value of 2.8 V, 2, row 1 ratio sensor value is 3.3 V. After the operation of the engine, an exhaust air-fuel ratio sensor 1 value gradually rises from 2.8 V to 3.3 V and variation in the vicinity of 3.3 V, while the air-fuel ratio sensor 1, row 2 is always in the vicinity of 3.3 V change (Table 2).
Table 2
For the relevant line has been previously checked, row 2 of the oxygen sensor 1 is no problem, but reversed peroxy sensor test, the engine the possibility of the control unit in question is relatively large, should be 1, row 1 values in the engine-fuel ratio sensor control unit converter circuit failure. When properly mixed gas of the engine, a discharge current ratio sensor 1 should be zero, but the actual value was (mixed gas concentration) is 2.8 V, the engine control unit in accordance with the signal, the correction value by -14 percentage long fuel (reducing percentage of the fuel injection quantity 14) reduces a cylinder, the cylinder 3 and the fuel injection amount of the cylinder 5, so that an exhaust gas is always lean mixture, resulting in the oxygen sensor 1, row 2 no change in value is always 0 V. The engine control unit 1, row 2 mistaken for an oxygen sensor is damaged, so the lightsEngine fault light. Since an exhaust gas is always lean mixture, excess oxygen, a burned exhaust catalytic converters.
According to the above analysis, the decision to replace the maintenance personnel engine control unit. But we found only 3.0 L engine control unit. Loading test. The ignition switch is turned on, when the engine does not start, 1 and 2, row 1, row 1 ratio sensor values are 3.3 V. Start the engine, in the various test conditions, the data flow was observed engine, row 1, row No. 1 and 2 values are 1 ratio sensor changes in the vicinity of 3.3 V. Engine data streams are normal. 1 and 2 but row 2, row 2 of the oxygen sensor value in most all conditions in the vicinity of 1 V, at a few time 0 V, since the control unit of the engine is substantially 3.0 L 2.5 L engine fuel injection ratio of large much, so the air-fuel mixture of a rich, resulting in two values in the oxygen sensor 1 V. in most of the time According to the above analysis and testing Alternatively, the engine control unit fault is determined.
Troubleshooting: Usually 2.5 L engine control unit, after the arrival of loading, we can see that the value 1, row 2 of the oxygen sensor may be normal variations, troubleshooting confirmation test.
(Fan Daogang)