Originally Posted by Proflyer

^ that's not true at all. Nitrogen is the biggest scam I think to hit the auto world lately. I hope everyone remembers that atmospheric air is about 78% nitrogen anyway...the only thing the nitrogen does is it is less temperature sensitive, but that's hardly an issue with passenger cars. Race cars/race motorcycles are a bit different but still, not a big deal. Also they use it in airplane tires (when they can) because of the huge temp swings.

If your tires leak at all or the valves leak at all (whcih is normal, you generally need to add air every few months) the nitrogen won't change that a bit. Instead, you'll just be paying $10/tire to fill them and then people think they need to 'change' the air if they can't get nitrogen.

Back to OP, obviously check air pressure, but speed and time will increase pressure, not decrease it, so that doesn't make a lot of sense. Only other thing I can think of is maybe the battery is going bad and at speed the sensor has a harder time reading it? Is the system wheel specific? If so, try a quick rotate and see if the issue moves. If not, then it's more likely an issue with that sensor in the wheel well.