Can an OBDII scanner consistently return the wrong code?

A few weeks ago I had my 2000 Ford Taurus serviced in response to a P0171 code (System Too Lean). They replaced the MAF sensor and PCV valve which fixed the problem.

The check engine light came back after a week, so I took the car back in. They read it but claimed it was a P0460, told me it was a $900 part (not counting labor) to fix, but recommended that I not repair it because of the car's age/worth.

The same P0171 code came back yet again a few days later. Now I don't know whether or not I can trust my code readers. Is it reasonable to assume that both of my (cheap) readers are getting the wrong code?

Can you keep a fully marked police cruiser in your driveway if you are not a police officer?

If you are working on a police vehicle project for show purposes, can you keep it in your driveway? I have a lot of vehicles driving by and I don't want to cause issues with local police agencies, I wouldn't drive it or anything either. It's also a Ford Explorer based on the Local Dept's Taurus. It's nearly complete, but I don't have anywhere to store it, my garage can't fit it and I need somewhere to keep it until I make room in the garage. I'm in Ohio BTW. Like I said, I don't want to drive it or anything, I just want to use it for show purposes and as personal collection. Does anyone know the law on this?

Power steering problem with a 1998 ford taurus?

Power steering problem with a 1998 ford taurus?

Added (1). we've been having trouble with the power steering, it starts to make a loud whining sound then when we check the fluid level while hot it shows low but if it sits and cools down its back to normal?

Added (2). just a update the fluid is also frothy when we checked it hot

Overheating (leaking?) 1999 ford taurus?

I just drove my '99 Taurus for about three hours. I topped off the coolant before I left and had no abnormal gauge reading along the way, but when I pulled into a parking lot and stopped the car, it leaked a huge puddle of what I can only assume is coolant/water and I could hear the whistling of air under pressure escaping. Do I have a blown head gasket? I feel like my temperature gauge is broken because it gave me no indication of high temperature on the drive. If there's something I can look for to indicate what went wrong that would be very helpful.