Posted by Traveler on October 19, 01 at 06:27:44:
In Reply to: '90 Suburban tune-up, plus HVAC system question posted by Foy on October 19, 01 at 06:07:29:
This works on computer equipped trucks up to and including 1995:
Straighten out a paperclip then bend it into a big "U".
Turn ignition on, engine not running. MIL "Malfunction Indicator Lamp" in instrument cluster is on steady. Insert the paper clip ends into terminals A and B on the Data Link Connector under the driver's side dash. A & B are on the upper row of the two rows and are the rightmost two sockets. The MIL will then begin flashing your codes. Each code repeats 3 times. For example, it should start with code 12: one flash, pause, two flashes, longer pause, repeat two more times. Write down your codes as they appear on the light. If code 12 flashes 3 times, then it starts code 12 over again, you have no trouble codes set. 12="no tach pulses". Remove the paper clip and the system is ready to run.