auto related / OBD2

The cheap code scanners are good enough for home work and as Dave says, a quick scan. Be advised of two things.
1) Most generic scanners will only read engine codes. You may have to go to a dealer for trans codes, bcm codes, air bag codes, etc. Most dealers will scan for free or a basic minimum. To verify some codes, diagnosis is required and will cost you. (egr and evap leaks come to mind) But they are only going to "free scan" the areas available to independent shops.
2) The rational behind the code is the ultra important. There are at least 5 codes I know of for a rear 02 sensor. To determine if it's a sensor problem, you need to know what the ecm is looking for, and how to provide it. That's where your online research comes into play.
If you think you are going to buy a scanner, tell the repair shop what part to replace, and NOT pay diagnostics, you can forget it.
If your just puttin' around the house, they are a useful tool.

First of all, be aware that these scanners will not work with most European vehicles. Many of those have their own system, and you have to take them to a dealer. Just another way to rip off customers. MB is the worst.

Second, there are a LOT of codes. Even with a decent code reader and a service manual (an absolute must) it will not necessarily tell you what the problem is. You may get a code that says a certain cylinder or cylinders are misfiring. That's it. You will have to figure out why. The codes will rarely tell you what parts need to be replaced. For that you need a very expensive piece of diagnostic equipment (several thousand dollars) and the vehicle manufacturers specific software for your vehicle. I have had the check engine light come on in my '01 Chevy Malibu several times, and would get a meaningless code that showed that one of several dozen parameters had been exceeded. In every case the light went out when the system was reset, and never came back.

A few years ago I purchased an Innova Can ODB2 Scan Tool (3100 model). While it does not do ODB1 it does a great job reading Diagnostic Trouble Codes (DTC's) including Manufacturer Specific DTC's, Freeze Frame Data, Real Time Data, Recording and Playback of Real Time Data, Indicators showing if various Test have been completed.

It came complete with the PC-Link kit allowing me to download the data from the tool to the PC and generate reports. The Link Kit also gives you the ability to update the tool with the latest DTC codes and Manufacturer DTC codes..

I have recently seen them offered at Walmart for under $100. It is the same unit I paid over $200 for and I now see it comes with the PC-Link Kit.

The 3140 also reads OBD1 codes and comes with all the various adapters for the older non standard interface. At Walmart for $199

The 3160 can also diagnose ABS codes. At Walmart for $199.... on sale

Its worth a look.

Henry

I hope everyone understands that the generic code readers, up to $5000 dollar scanners will not tell them exactly what the problem is. Capabilities are nice, sure. But they only give you a direction to start looking. I say this only because I have a large number of people that stop in thinking exactly that. I have to tell them plugging in my scanner does not do anything like that. It is not made with any magical nor mystical powers. It still takes a good technician to figure out many problems.
This mornings problem vehicle is just such a beast. 07 Escalade comes in with full tank of gas and gauge reads empty. Gauge sweeps when started which means the problem is not with the gauge assembly. One would think immediately fuel sending unit. Right? Nope. The signal wire from the pump to the pcm was rubbed through from the rear of the front driveshaft, along with 2 other wires. This wiring loom was still factory secured, but had enough slack to occasionally touch the driveshaft. 100,000mi later, no more gas gauge. Repair wires, and zip tie the loom back further away from the driveshaft.
I also know there are many resourceful people on this board that are seemingly capable of mystical feats. So please take no offense. Just making sure nobody is under the illusion that a scanner will point directly at the cause of a problem. OP seems to found this is the case for this problem so far.

When my Chev PU check engine light came on I bought an Innova. It's the one that reads obd 1 and 2. It was kinda spendy but I figured I'd try and get a decent one if I was going to spend money. I plugged it in and it said it was an O2 sensor. So I bought an O2 sensor and the light went out. Didn't even have to install it! Isn't life great sometimes? It's been about 3 years now and the sensor is still sitting on the shelf. Now when the light comes on I fill it up with some decent gas and put my foot into it once in a while and the light goes out. I guess I drive like an old man.

Anyway, the cheap way for you is to quickly turn the key to the on position then off three times. (Not start just on.) The battery light should start flashing any codes. Three flashes, nothing, two flashes, nothing, 5 flashes = code 325. It works in a pinch but still easier to buy a scanner so make sure you get it right. Spend just enough to get one that you can clear the codes as not all will. The check engine light is the only one that will never burn out.