Your GMC Sierra is equipped with an On-Board Diagnostics (OBD II). The OBD
II system monitors all aspects of your GMC's emissions system and reports
information to the OBDII computer. The data is processed and checked against
the computer's pre-determined values for various inputs levels and
performance patterns of your vehicle. If any problems are found the computer
will determine whether to alert the driver or not.
It appears during your recent repair of the exhaust valve your trucks OBD II
computer system was reset; erasing all the emission monitors (readiness
flags) from the OBD II computer. Setting the emission monitors requires
driving your truck at least 200 miles; consisting of everyday normal
driving, stop and starts (like at red lights and traffic), ignition on and
off several times a day with at least 15 minute causes in between (this
allows the EVAP monitor to run), and freeway driving at least on three
occasions for at least 15 minutes each at speeds above 30 mph.
After these driving conditions are met and your GMC still fails the OBD II
portion of the smog check, we can only recommend a smog check repair center
conduct a diagnosis of the OBD II computer as to clues of why the monitors
are not setting. Assuming no Check Engine light or Malfunction Indicator
Lamp is illuminated we have to suspect your vehicle's only problem is simply
not enough drive time yet.
:
As far as spending $30 for a retest on and on... We can only recommend you
build a good relationship with your smog station, promise you will send them
all your business and recommend them to all your family and friends, and ask
that they simply connect their scan tool to your truck only to inspect if
all the monitors have set; prior to doing an actual smog test. Plugging in
the scan tool and retrieving monitor data is fairly easy to do.
