1996 Chevrolet Silverado check engine light on

"Live data" simply means you can see a list of what the computer is seeing. For example, if it's 60 degrees outside, you'd expect to see the ambient air temperature sensor listed at 60 degrees. The coolant temperature sensor would be too until the engine started to warm up, then you'd see the temperature the sensor is reporting to the computer. You will see the brake light switch, cruise control switches, and various relays listed along with their "state", meaning whether they're turned on or off. If you're pressing the brake pedal and the brake light switch is listed as "released", you'd know to look in that circuit to see why the computer isn't seeing that switch being activated.

Under "Inputs and Outputs" you'll also see those switches but you'll be able to command those things on and off. A typical use for this is when troubleshooting a dead radiator fan. You'd have to drive the car long enough for fan operation to be needed, then do your testing before the engine cools down enough for the fan to turn off. That might only give you ten to twenty seconds to do your testing. Instead, you use the scanner to command the fan to run. That allows you to make tests at your leisure. Without even having to run the engine.

You can also watch these things during a test drive. Most scanners have a record feature that allows you to record a few seconds of data that can be reviewed slowly later. That's useful for those times you have an intermittent hiccup that doesn't occur very often. By replaying the events, you can see which sensor readings changed for a fraction of a second, then went back to normal.

Chrysler has a lot of specialty diagnostic manuals to use with their scanners. Those show pictures of where to take readings and they provide charts with "yes" and "no" questions to answer, then they direct you to the next test. I've never seen those kinds of manuals for any other manufacturer, but there are some aftermarket scanners that have a test section where they tell you which color wire to take the reading on and what to expect for results. Other than the Snapon scanners, I don't know which other ones have that feature. That's why you have to look through them on eBay and see if anyone tells you if those things are included.

I just did a search for "Automotive scanner" and 268 items came up. The first one on the list is an older Snapon MT2500. We called those "the red brick". This might be a good choice. They use a pair of plug-in cartridges that do not need to be updated, but you have to be sure you have the right ones for your cars. They sold a lot of these, and as a result, there's a pile of them for sale now since shops have had to upgrade numerous times since these came out. I saw one of these listed for $150.00 which is a real good deal. If you see a new scanner listed for less than a few hundred dollars, you'll be disappointed if you compare it to the more expensive stuff. Some of these cheapies take a long time to update the readings that they're displaying. A lot can happen and be missed while you're waiting for the numbers to update.

There's an "Enhanced Monitor 4000 on the list too. That's the updated version of the first scanner I ever bought. I like it a lot and still use it.