Locate the Diagnostic Link Connector (DLC) port. In a 1998 Tahoe, it's usually found under the dashboard, on the driver's side.
Ensure that the vehicle is turned off.
Retrieve a jumper wire or a similar tool that will allow you to connect two terminals in the DLC port.
Open the DLC port cover and identify the terminals labeled "A" and "B."
Insert one end of the jumper wire into terminal "A" and the other end into terminal "B."
Turn the ignition key to the "ON" position, but do not start the engine.
Leave the jumper wire connected for approximately 10 seconds.
Turn the ignition key back to the "OFF" position.
Remove the jumper wire from the DLC port.
Start the engine and verify that the service engine soon light has been reset.
