I found this via google groups, hope it helps (the author was ayeldram with a
address, no sig in original post)
There is 3 pin plastic connector sticking our of the middle console
next to drivers right foot, jumper pin 1 and 3 with a paper clip when
the Key is "ON" position but truck is NOT running.
The "check Engige" light will start flashing, it will flash each code
for 3 times. It is a 2 digit code it will flash the first digit then
pause and flash the 2nd digit, then lognger pause. e.g
flash-flash-flash-flash Pause flash-flash-flash-flash would be "44".
Once get the code either look at the Haynes manual or search the web
for what it means.
Ignore first code, which is 12 and it will flash for 3 times. All it
means it that computer is getting into the diag mode and also give you
enough time to get ready to observe the real code.
By the way "44" is the one which means Lean condition which could be
contributed to the O2 sensor or EGR Valve.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.