When I bought my car, the tires were filled with nitrogen and even had the little valve stem caps saying so. I had a staple and a screw in the right rear. I pulled the tire and plugged both holes and aired the tire up. All my tires are at 35 psi. My tire pressure monitor still goes off even after resetting it. Do you think the compression difference between air and nitrogen makes a difference? (I didn't refill the one tire with nitrogen).

The difference in air and nitrogen is indistinguishable to the PCM. Our pressure monitor isn't really one, per se. It measure'* tire revolutions on all four by way of the wheel speed sensors. You have to get them all exactly the same pressure, and then with the tire pressure fault showing on the DIC, hold the reset button down while moving. This allows the PCM to re-register it'* readings. Just resetting it with the car stopped clears it from the DIC display but doesnt restore the fault stored in the PCM.

That got it - thanks!