There are two items available.
Code readers and code scanners.
The reader will only give you the codes that are set at the time of testing.
The scanner will not only give you the codes set as well as transient codes, but will allow you to watch the individual sensors to see them in action while driving to catch intermittant problems.
I was having engine light problems a year ago and took my 96 Trooper to Auto Zone to have the codes read. It spit out several codes. Talked to mechanics who gave me opinions from "you can't always tell from the codes" to "that sounds like you have several problems."
I wrote down the codes and reset the computer. several weeks later the engine light returned. Back to Auto Zone for a reading of codes resulting in several totally different codes from the first time. Mechanic opinions were the same as first time including "we can change this and if that doesn't fix it we can try this..."
I did some extensive research and found that I definitely wanted a scanner not reader. I also found that scanners cost $450-$1500+. Out of my ballpark. Many also did not support Isuzu. I settled on Auto Xray brand because they specifically supported Isuzu. http://www.autoxray.com/default.htm
Now to get arround the $499 price tag. I found that they make a model specificcaly for OBD II of which all 1996+ Isuzu's are. This model doesn't include all the expensive cables and adapters to test US car models. The model is currently called EZ-LINK OBD-II SCANNER. http://www.autoxray.com/products.aspx?sub=scanners&id=2
I went to my trusty bargain basement E-bay.
I bid on several that went for $300-$400. Too much. Finally late one night I bid on one and got it for $185.
I plugged it in got all the numerous trouble codes both stored and trasient. Upon driving I noticed one of the O2 sensors was going haywire upon getting hot. Replaced sensor and problem has not returned in several months. Also in the last several months I got a throttle position sensor code showing up intermittantly. Pulled the plug, found corrosion, cleaned up, problem gone. I recently took a 30 day vacation and logged 6800 miles with not so much as a burp out of the system.
I am a 100% satisfied customer and spent less money than the Isuzu dealer wanted just to troubleshoot the system.
Howdy folks. I just wanted to add a little to what jdeal was saying. Yes, there is a HUGH difference between readers and scanners. And yes, one can easily spend upwards of $5K on a good scan tool and all the related attachments. And yes, the Auto X-ray is a good tool for the hobby mechanic, and probably the best "bang for your buck" option. However, if you use them everyday, the Auto X-ray does lack in some areas, which I won't get into. The main differences have to do with the amount of accuracy and the frequency of sampling. The Snap-On and OTC scanners are my personal favorites.
Anyway, first of all, the guys at the parts counters are not technicians/mechanics, and trusting their opinions can easily lead you down the wrong road. I do have to defend myself and other REAL techs here though. When someone is asking me a question, there are always at least 15 things that pop into my head on what the related problem could be. Code readers and also code scanners are tools, and nothing else. They can lead you in the right direction, but definately do not tell you what is wrong. You have to get in there to find out. Like jdeal was working with his TP sensor. Just because you got the code, did you know it was a corrosion problem? Did the scanner TELL you that? Could have been a bad wire, bad sensor, bad harness connection, or bad ECU, etc. My point is that a tool is only as good as the tech/mechanic who is using it. (Jdeal I'm not picking on you, only using your example as my own, no offense)
When you do go to a shop just remember, you are paying for the training, expertise and experience of your mechanic. Not to mention the enormous cost of equipment, insurance, etc. Think about how difficult it is when someone says, "I've got this funny noise, it's kinda a growl, whizz noise coming from the inside of the motor. What is that?" And then the customer wants you to look into it for free or gets mad when you charge them for diagnosing and not repairing the problem. Time equals money. And nothing enters and leaves my shop for free, just like the doctor's office. If you're looking for a more economic alternative, look into your local community college or high school automotive programs.
great thread guys! it already answered many questions i had. my mechanic has about $1800.00 in his OBD equipment and software so, i was leary of the $50.00 harbor freight stuff. i think now i'll stick to just paying him to diagnose the stuff i can't figure out. cool equipment though, especially being able to monitor your engine while you are driving. is there anything else out there that can do diagnostics of the engine while you are driving?
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