The Chevy Tahoe is equipped with an onboard diagnostics computer that stores trouble codes sent to it from sensors positioned throughout the vehicle. When a sensor detects a malfunction, it sends the trouble code to the computer, which either makes an adjustment or illuminates a warning light on your dashboard instrument panel. You can read these diagnostic codes using a handheld computerized device called an OBD scan tool. You can get these tools from your local auto parts retailer. After you have read the code and had the problem addressed by a qualified mechanic, then you can reset the codes. Never reset the codes before you fix the problem, or the warning and service lights will turn themselves back on -- or worse, your diagnostics computer could make false readings.
Locate the diagnostics port near the fuse panel on the underside of the driver-side dashboard. This port should be the same shape and size as the connector on the OBD scan tool. Plug the OBD scan tool into this port, taking care not to push too hard because this could bend the pins inside the plug.
Put the key into the ignition and turn it to the "on" position, but don't start the engine. This will power on the scan tool.
Wait while the scanner reads the codes. Look for a command on the scanner that says "delete" or some similar command and select it. This will erase the codes and reset the computer.
Unplug the scan tool and start the engine. Verify on the instrument panel that all warning and service lights have shut off.
