I just bought a little bluetooth Automotive Diagnostic Scanner from Amazon for under $10, and I love this little sucker.

My check engine light came on, so I went to AutoZone and had them plug in their scanner to pull the codes for me. While researching the fix (a bad oxygen sensor) I stumbled across this thing.

It is a small little bluetooth device that you plug into the port on your car/truck. You pair it with your computer/phone/tablet and it allow you to read error codes, clear codes, and it will give you real time data on pretty much any sensor in your motor - rpm, coolant temp, throttle position, vacuum, fuel consumption - you name it - if there is a sensor reporting data - you can read it right on your phone.

There are a bunch of free apps, but I purchased an app called Torque for $5.

The only down side is that this model does NOT work with my iPhone. They make a wifi version that does. But I went out and bought a virgin mobile Android phone for $30 that I am not going to activate, but use exclusively as a monitor. I plan on hard wiring it into my sun visor this weekend.

http://www.amazon.com/gp/product/B0076KBPNI/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1