How do ya get the code?

[Scott Shotton]

ECMnut at aol.com wrote:
> 
> Hey gang,
> 
>  My friend is having "CHECK ENGINE" light blues on a 94 GrandAmm.
> The Diacom doesn't work with the 94 & newer OBD stuff.
> 
> Can someone tell me how to get, and interperate the
>  error code that is stored?  If it means sending me to a website
> somewhere, that's okay.  I know you can get it to blink the
> check engine light, and count the flashes, then look the up the
> code, yada...
> 
> Not sure how to do it on a vehicle that is this new.
> TIA
> Mike V.


You can't do flash code diagnosis on an OBDII vehicle (that I am aware
of).  The 96+ regulations require a common connecter, codes, and
connector location, along with special PCM functions.  A serial data
line is required to transmit these "universal codes" and a specific pin
of the diagnostic connector has been identified.  However, extra pins
have been provided.  The manufacturer (in this case GM) can include a
second serial data line with more codes and information that may only be
avaliable to specific (ie GM techII) scantools.  Flash codes are
becoming a thing of the past.  A scan tool will be required to retrieve
codes from an OBDII vehicle.

On the other hand, there are more codes and they are more specific.  For
example:  Ford 3.8L engines frequently blow head gaskets.  Almost
always, cylinder #4 blows first.  By the time another cylinder gos, the
car is running like poop!  So the "95 Windstar" comes into the shop with
poor heat, occationally runs rough, and losses coolant (with no sign of
a leak), I know it has a blown head gasket.  Plug in to the ALDL and
read codes.  Misfire Cyl #4 code is set.  Bamm!  $1500. later, you are
the proud owner of new head gaskets.  

The PCM for an OBDII vehicle processes much more info.  The cyl #4 code
was determined by slight variations in crank shaft speed.  If you ask
me, that is pretty damn accurate information.

Another example of OBDII PCM sensitivity:  on startup, the PCM performs
a number of checks.  One is of the Canister purge system.  It closes a
solenoid and applies vacuum to the purge lines and fuel tank.  If the
system does not hold vacuum for a specified amount of time, it sets a
EVAP code.  So, if a gas cap is not tightened all the way, it could leak
vacuum.  If the tank leaks vacuum the PCM sets a code.  If the PCM sets
a code the SES light comes on.

My point:  It could be something simple or complex.  Check the basics
first.  Find someone with an OBDII compatible scantool second.

I am attending a Chrysler OBDII seminar later this month.  If I hear
anything different, I will post it.

Hope I helped.

Later


Scott