Oxygen Sensor - Rear 2002 windstar

went for inspection today and fail was told that auto running rich and that both rear oxygen sensor value not going moving up and down i will change both sense but does this sound right, is there a way to test them,i have no trouble codes and no check engine lite

thanks frank

You will have 4 oxygen sensors.....2 for the front bank of cylinders, and 2 for the rear bank of cylinders.

Each band of cylinders has a "upstream" sensor, which is used by the PCM (computer) to adjust the air / fuel mixture.......and a "downstream" sensor that is used ONLY to monitor the catalytic converter to make sure that it is working.

Upstream is before the catalytic converter......mounted in the exhaust pipe between the exhaust manifold, and the catalytic converter.

Downstream is after the catalytic converter, mounted in the exhaust pipe between the catalytic converter and the "Y" where the 2 exhaust pipes merg into 1 pipe.....in front of the muffler.

They should have told you which bank was rich. If both banks.....very unusual for both oxygen sensors to fail at the same time.
Perhaps a more in depth diagnosis is in order.
Most auto part stores, like AutoZone will read your failure codes for FREE.
I would have this done......make sure to write down the exact code(s) that they give you......as the codes will tell you which of the 4 oxygen sensors is giving the code....and exactly what is wrong.
Better than changing all 4 oxygen sensors at roughly $50 each......and often it is NOT even a oxygen sensor that is bad......could even be a perfectly good oxygen sensor reporting a valid problem condition (like a bad catalytic converter, etc).

i have a obII reader and there are no codes or cel light, where they got a rich reading they connected the computer, he sshow me the screen that they frount sensr were changing in value and the rear ones was not,is there a software program you can use to test the engine with the a laptop,

thanks frank

If you were to monitor the voltage output from the oxygen sensors, the upstream sensor output will "oscillate" between two voltages (when the PCM is operating in 'closed loop'), regularly changing from a low to high voltage, then back to a low voltage. On the other hand, the downstream sensor voltage output will be steady, only varying with the engine operating conditions and loads.

As mentioned, the downstream sensor is there to test the catalytic converter. This is accomplished in the windstar by making sure that the regular variations seen in the upstream sensor are trapped by the catalytic converter.

The upshot of this is that the rear sensor is "steady" when the sensor and the catalytic converter are working correctly.

The PCM constantly checks each sensor for proper operation. When if finds one of the sensors is "dead" (as your mechanic is saying), or malfuntioning in some other way (there are several tests performed) it will detect it, store a code, and turn on the CEL. Personally, I would not replace a downstream sensor unless there was a code.

I am not aware of the legal requirements for vehicle inspections, but I was under the impression that a PCM that does not report codes would pass emissions. Is this true for New York? Would it be worth to call another mechanic to check? As mentioned, the sensors are at least $50-$60 each.

Regarding testing your O2 sensor, try this link:

http://mr2.com/TEXT/O2_Sensor.html

I would have the vehicle checked at another station.
A non-switching upstream sensor WILL set a code and light the CEL.
The downstream sensors switch very slowly, it DOES take some time for the complete OBDII system test to complete when the codes(s) are cleared / reset and, from what I have read, the downstream sensor test is the one that takes the longest to complete.

However, IF the downstream sensor is truely not switching, then the OBDII system WILL set a code indicating this.....telling you which sensor and exactly what state it is staying in.

It sounds like a shop could be trying to drum up some business, or the mechanic is not up on what they are doing (I have run across both situations).
A 2nd opinion is in order, as this is not sounding normal.