Help everyone- I have an Arduino Uno that I had setup today being powered by a pc. I was getting a strange reading on a sensor so I measured the 3.3v pin it was connected to and it read the same as the 5v output pins. In this case 5.11v. This was also true on the aref pin.
What might be the problem?
Anthony
Something is not wired correctly or the sensor output is not correct for the intended use etc.
Sensor manufacturer and part number?
Datasheet?
Wiring diagram?
so I measured the 3.3v pin it was connected to and it read the same as the 5v output pins
Is the 3.3V pin OK when nothing is connected?
No it still has the wrong voltage even with all connections pulled. Could something be bad? Could it be a poor knockoff?
Anthony
Until you provide complete documentation for the sensor and your wiring, we will have no further suggestions. 
(Except for gilshultz that is. 
)
aiannar974:
No it still has the wrong voltage even with all connections pulled. Could something be bad? Could it be a poor knockoff?Anthony
A bare Uno powered from any power source with 5V on the 3.3V pin is likely to have a short that is findable and fixable.
Nothing on the Uno board uses 3.3V so if you can't fix it, it is still usable.
Before doing any testing disconnect everything and measure one more time. If it stays at 5 volts I would guess you fried the 3.3 volt regulator which has its input shorted to its output. The reason for this is it is supplied by the 5V regulator which is the output you are getting. Without physically having the device look if it got hot and the solder shorted some pads. The easiest way to validate this is to remove it and the 3.3 volts will go to about zero with a light load maybe a few K ohms. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
Where was the volt meter's black probe connected? What was the voltage on the 5V pin? The VIN pin? Connect a 220Ω resistor from 3V3 pin to GND and test again. Post a link to the UNO seller's web page.
Thanks Everyone- I will do this after work today.
Thank you,
Anthony