GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Service Flags



Vehicles equipped with the C-4 system have an emission indicator flag which will appear in the odometer window when service is necessary. The flags are marked SENSOR, EMISSION, and CATALYST, depending on the device that is scheduled for regular maintenance.

To reset the flag, first remove the instrument panel trim plate and cluster cover lens. There are reset notches on the drivers side of the indicator flag. Insert a long, pointed probe diagonally into the detents on the upper left side and rotate the flag downward until an alignment mark becomes visible in the left side of the odometer window. Once the flag has been reset, replace the cluster lens and trim plate.

C-4 and CCC vehicles are equipped with a Service Engine Soon or Check Engine light. This light is on the instrument panel below the fuel gauge. The light will come ON during engine start-up to let you know the bulb is working. Have the system checked by your dealer if the light does not come on during start-up or if the light illuminates intermittently or continuously while driving. These conditions may indicate that the Computer Command Control system is in need of service. In most cases, the vehicle will not have to be towed, but the vehicle should be serviced as soon as possible.

For more information about the service light, refer to Computer Command Control section in this section.