Computers and Control Systems: Service and Repair

Fig. 114 Malfunction Indicator (CHECK) Light Reset:

In addition to displaying computer system malfunction codes (codes only on California models), the Malfunction Indicator (CHECK) Light on Federal trucks acts as an emission maintenance warning. The Malfunction Indicator (CHECK) Light will come on at 80,000 miles indicating that the Oxygen sensor service is required.
To reset the warning light (after servicing the Oxygen sensor). Remove the instrument cluster. Instrument Cluster / Carrier Locate lettered reset holes (NC and NO) on the rear of the instrument cluster. Remove the screw from the lettered reset hole and reinstall it in the other hole.