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  As is known,   correct work of the petrol engine needs the certain ratio between volumes of acting fuel and air. The ratio (14,7:1) theoretically is the optimal by criterion of full combustion and refers to as factor of surplus of air a =1 (rice 1). Purpose (assignment) of an electronic control system by submission of fuel is maintenance of this ratio in a proportion most appropriate to temperature conditions, loading on the engine, to sufficient dynamics (changes) of dispersal, requirements of profitability and protection of an environment.
  The factor of surplus of air a, is measured by Oxygen Sensor (O2S) which is located in a final collector. At  a=1 the mix is optimum (rice 2). On some types of automobiles after the catalyst the additional gauge for the account of "ageing" of the basic and the analysis of a condition of the catalyst is established. Depending on a pressure (voltage) of a probe, ECM corrects parameters of a fuel-air mix. 
     At warm the engine and serviceable system fuel injection system, ECM and a probe are in the closed system of regulation, i.e. in a mode with the closed feedback - " Closed  Mode ". ECM constantly traces  a target voltage of a probe. At increase of this voltage - reduces time of opening of atomizers. At too poor mix (a low target pressure (voltage) of a probe) - increases a little. 
At faulty Oxygen Sensor ECU passes in a mode at which indications of a probe are not taken into account for definition of parameters of a fuel-air mixture (i.e. a mode without a feedback on a target voltage of the gauge of the maintenance (contents) of oxygen - " Open Loop ").
   Attempts of replacement of "regular" probe O₂The simulator on engines 1G-GE, 3S-FE have shown, that at the best ECU ignores "... brains " at submission on his (its) input (entrance)  of pulses of a voltage of the appropriate frequency, amplitude and duration and from enough high-resistance source.
 The ambassador connection of the simulator on appropriate input (entrance) ECM pulses of a voltage, BUT absolutely not synchronously with his (its) attempts to change structure of a mix act. At submission of a constant voltage from an external source (for example, from the parametrical stabilizer on the diode), changes of a voltage DO NOT OCCUR at all! I.e. ECM in general "does not see" change of structure of a fuel mix that should occur at absence of submission of fuel in a mode compulsory idle (in a situation at which the pedal of gas is released (let off), but revolutions of the engine still big).
   As consequence (investigation), in both cases it (he) passes  from a mode " with a feedback " in a mode at which indications of the Oxygen Sensor are not taken into account at management of submission of fuel. Described reaction  ECM to the simulator is characteristic not only for Toyota, but also for fuel injection systems of other manufacturers.
Zirconia Oxygen Sensor represents the ceramic case in which platinum electrodes are established. One of them is in a stream of exhaust gases, and the second in an atmosphere. At high temperature ceramics ZrO₂ Alloyed  is firm electrolyte, i.e. will carry out (spend) ions of oxygen. Between platinum electrodes  the potential difference which characterizes a degree of enrichment of a fuel-air mix (Rice 2) is created. Application Pb gasoline in systems with  is inadmissible, since causes "poisoning" of platinum.
   In some engines probes with heaters electrodes are used (HO2S). The active ceramic element of such probe has an internal heater that indications of a probe were authentic even at low temperature of the fulfilled gases. It is necessary to note, that decrease (reduction) of sensitivity, reduction of speed) ECU does not fix some malfunctions Oxygen Sensor. Therefore and to judge serviceability  it is possible only after the appropriate check instead of to be limited only to reading of codes of self-diagnostics. To check a target voltage (an oscilloscope, a tester) it is necessary being connected to for an alarm wire of a probe at working and warm the engine. In figure it is given diagrams of a target voltage of the gauge of the maintenance (output voltage) of Oxygen Sensor (k4), revolutions (rpm) of the engine (W2), time (injectors pulse) of opening of injectors  (t5) at idle for engine. Appreciably, that the system functions at the closed feedback on day off of a pressure (voltage) of a probe (" closed mode "). ECU reduces time of opening of injectors at increase of target output voltage from the Oxygen Sensor. And on the contrary, at a poor mix - increases.

Fig.3

From higher told follows, that in this mode authentic check of speed (a constant of time) the gauge IS NOT POSSIBLE. Time of increase (as well as time of reduction) his (its) target voltage depends not only and not so much on his (its) dynamic properties, and from a "program" constant of time fuel injection systems. I.e. from step-type behavior of an increment of duration of the following pulse of a voltage managing an atomizer. Check of speed of a probe on his (its) target voltage is possible (probable) only at the analysis of his (its) target voltage after " compulsory single " a course or at Vf1-diagnostics. 
    The resource of the gauge of the maintenance (contents) of oxygen in exhaust gases usually makes tens thousand kms and substantially depends on conditions of operation.  Decrease (reduction) of a resource of probes provokes application Pb gasoline, low standard oil rings, hit in exhaust system antifreeze. Resistance of a heating element usually makes from 1.2 up to 15 Ohm.
  Oxygen Sensor is increase of the charge of fuel, increase of the maintenance (contents) WITH, deterioration of dynamics (changes) of dispersal of the automobile, occurrence unstable idling. Thus reading the appropriate code of malfunction is possible at initialization of self-diagnostics. Malfunction of a probe can provoke failure of the catalyst converter and (or) cause wrong functioning of EGR system.
  Independent check of a condition of a probe is possible (probable). Check of a condition of a probe at diagnostics of the reasons of malfunction of fuel system by technicians HUNDRED - is obligatory. But before its (her) realization it is necessary to learn (find out) quotations for the herein provided diagnostic works. 
" Round eyes " or arrangements: "... And what for to you it to check... " Should guard at an estimation of qualification of executors and desire to concern them. The diagnosis: "... At you " dead Lambda... " Should prove to be true in objective parameters, instead of simply "argument": - I so see...

I pay your attention that before manufacturing of an adapter for use of Oxygen Sensor from BOSCH under the sketch http: // lexa38.narod.ru/lambda_k.html, measure distance centre to centre fixing apertures of a "native" probe. At the top probe it is equal 44 mm, at the bottom 38 mm.
  Check up an oscilloscope a target voltage of a probe at idle and at compulsory idle - deceleration (i.e. at the released pedal of accelertor, but enough the big revolutions of the engine when it is carried out "not" submissions of fuel) and compare to diagrams:
Fig.4

 Conclusion about necessity of replacement Oxygen Sensor only on the basis of that " his (its) constantly low target voltage at idle " - premature. This necessary, but not a sufficient condition of replacement. For example, at not tightness of an inlet collector (so-called "...air ") the engine will work at too poor mix, a target voltage of a probe will be low, but the probe thus "will be not guilty"...
  If the target voltage of a probe on  idle engine constantly is more 0,5. 0,6 Volt it is necessary to check up time of opening of atomizers on idle, pressure in fuel system, standard of the gauge of temperature for ECU,  the gauge of underpressure or a stream of air to be convinced of tightness of atomizers.
 If a Heaters Oxygen Sensor  (3 or 4 contact), check up resistance of a heater of a probe and receipt on him (it) (on a heater) voltage 12 V.

 If as a result of carried out (spent) diagnostics appears that the probe it is necessary to replace it (him) is faulty. The variant malfunctions of the catalyst or his (its) Overwarm-gauge  is not excluded. Sometimes the reason of that the indicator " Check Engine " ("MIL") continues to shine at the entered engine, negligence of technicians is at realization of repair work. For example inclusion of ignition at the removed (taken off) socket of any unit injection systems, including and Oxygen Sensor.

 The target voltage of a probe can be checked up the voltmeter or the indicator. 
Positive experience of replacements of "native" probes on " Lambda-probes " BOSCH " LSH 25 0 258 005 133 " (4 contact, 2 white wires - heater, black - output, grey - gnd and availability of their price, allows to recommend this variant as alternative to purchase "firm" Oxygen Sensor. At least, you risk 4 hundred Russian roubles (RUR), instead of 100-240 US$...
In Moscow market " Southern port " is flooded enough with these gauges of the maintenance(contents) of oxygen and on quite reasonable price (400 RUR). 
Look diagrams of a target pressure(voltage) of probes and practice of their replacement on engines Mazda  Mitsubishi
 

At replacement by  4 contact probe it is necessary one wire of a heater and gnd ("minus")  it is reliable to connect to the case of the automobile. The second wire of a heater is necessary for connecting to contact, on which always "+" after inclusion "IGN". Connection to contact "+" coils of ignition is inexpedient, since some systems use additional "extinguishing" resistance in a circuit of a feed (meal) of the coil, and also because of substantial growth ... loadings on this electric circuit at cold heater Oxygen Sensor. Connection to contacts of the fuel pump sometimes toilfully enough. In my opinion, it is necessary to use contact "IGN1,2" the lock of ignition.
The technique of check of a condition of , the description of basic differences  titania and zirconia Oxygen Sensor (Lambda-probes are stated in a separate material. Parameters of Lambda-probe BOSCH for fuel Inject. systems the VAZ are given in a separate note.
It agrees Toyota factory service manuals since 1997 in Fuel-Inject. systems of automobiles let out under standards California-emission, it is used AIR/FUEL (A/F) sensors. The A/F sensor signal voltage varies accordingto the amount of oxygen sensors in the ehhaust stream (see figure). Unlike the signal voltage from a heated oxygen sensors (HO₂S), the A/F sensors signal voltage increases as the air-fuel mixture leans and decreases as the air-fuel mixture richens. The signal voltage ranges from 0.48 to 0.80 volts! In a 1999 Camry voltage that corresponds with a specific A/F ratio is above  (to 4.0 Volts).While the vehicle runs in closed loop mode, the ECU uses the A/F sensor signal to lengthen or shorten the fuel injector pulse width until attaining a stoichiometric air-fuel mixture.

 The A/F sensor containts a ECU-controlled heater. At start-up, the heater helps warm the A/F sensors to quickly operating temperature. With minimal exhaust gas flow, the heater keeps the A/F sensor from cooling down. Other inform is in http://www.alflash.narod.ru/o2calif.htm