[AT] O/T Tow truck OBD II question

[Henry Miller]

Most of what you asked has been covered already, so I'll just add some general 
info that may be of interest to those thinking about getting a tool like 
this.

I work for a company that makes these things (not the one you bought - ours 
doesn't interface to your computer, and costs about 40 times more 
$$$).   As a general rule I recommend you not buy one of these things unless 
you like the gadget.   They can tell you a lot of interesting things, but 
standards change all the time.  Sure your tool will work with your current 
cars, but will it work with a 2010 car?  If yours doesn't cover CAN it won't 
work with some 2003 cars, otherwise I'd guess it will work for about 10 more 
years - but that is just a guess.  After that you can assume the electronics 
are different enough that it won't work.  (So far new tools all work with old 
cars - we have had to ship non-road worth cars in to we can test our tools 
only time will tell if this trend continues)

If you just want to fix your car the best thing to do is borrow the tool from 
your local auto parts store.   That way you are sure the tool is up to date, 
and it may be a higher end model that can diagnose your specific car, and not 
just the generic OBDII (generic OBDII covers about 90% of what you need to 
fix the car, but if you are curious about the car in general it is about 15% 
of what you you can get).   If your local auto parts store doesn't have a 
reasonable policy for borrowing tools find a different store - nearly all 
will read the codes for free, and just require a deposit to borrow the tool.  
(For that matter, any good auto parts store will let you use a lot of other 
tools as well - they want you to buy parts)  

That said, they are cool to have, and there is nothing wrong with buying one.  
In fact for your specific case it may be a good idea just because you can 
have someone drive around while you watch things in real time, and hopefully 
you can see exactly what was happening when something went wrong.   However 
don't get your hopes up, you have to be looking at the right time.

Before doing anything, remember you are still dealing with a standard 4 cycle 
engine.  Even though there are now computers and fuel injection involved, 
there is no fundamental difference between your modern car and your antique 
tractor.   The only difference is often in your favor - the computer can 
often (but not always as most of us have learned the hard way) diagnose 
problems that you would let slide on a tractor as too hard to understand.

One danger you can run into with these tools is reading codes and not checking 
to see if it is a real problem, or a one time thing.  Often the computer will 
set "pending codes", which means the computer saw something that looked 
wrong, but it isn't sure.   If the problem continues for a while the computer 
will turn on the check engine light, otherwise it will clear the code.   If 
you read the codes all the time, you can see the pending codes and think 
something is wrong when all is well.  (Of course if you can tell there is a 
problem the pending code may lead you to the cause before the computer is 
sure.   All I'm saying is be careful about doing something unneeded)

To understand the data in general, the best place to look is in the factory 
service manual.   I'm not sure how much is in them (generally they cover more 
how to rebuild the parts and less diagnostics), but nobody should work on a 
car without the factory manual.   Don't cheap out with the Chilton or Haynes 
manuals, get the OEM book.