GMC 1993 Safari Owner's Manual page 279

The Maintenance Schedule will tell you how often to lubricate these items.
See "Recommended Fluids and Lubricants" in the Index for the proper
lubricant to use.
Lock Cylinders
To be sure your locks operate properly, they must be lubricated. The
Maintenance Schedule will tell you how often to lubricate them. See
"Recommended Fluids and Lubricants" in the Index for the proper lubricant to
use.
You should not use penetrating oils because they could wash out the factory
installed lubricant and cause the lock to bind. De-icers which contain alcohol
could also wash away the lubricant, so be sure to lubricate the lock after
using a de-icer of this type.
Exhaust System
To help prevent damage to your exhaust system, do not continue to drive
your vehicle if you notice:
Engine misfiring
Loss of performance
Other unusual operating conditions
Have your engine and exhaust system serviced regularly.
Three- Way Catalytic Converter
Your vehicle's three-way catalytic converter is designed to reduce the
pollutants in your vehicle's exhaust. Use only unleaded fuel in your vehicle. If
you use leaded fuel, you could damage your three-way catalytic converter,
and other emission control components.
Malfunction Indicator Lamp (SERVICE ENGINE SOON light)
The Malfunction Indicator Lamp (SERVICE ENGINE SOONlight) on your
instrument panel lets you know when your emission system needs service.
The light will come on briefly when you start your engine to let you know
that the system is working. If it does not come on when you start your
engine, or if it comes on and stays on while you're driving, your system may
need service. Your vehicle should still be driveable, but you should have your
system serviced right away.
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