Buick 1994 Roadmaster Owner's Manual page 126

After changing the engine oil, the system
must
be
reset.
Malfunction Indicator 'Lamp
(Service Engine Soon Light)
1
The reset button is on the end of the instrument panel on
the driver's side behind the fuse panel door. With the
ignition key in the RUN position, but the engine not
started, push the reset button, holding it in until the
"Change Oil" light flashes and then goes off. This
indicates the Oil Life Monitor System has been reset.
SERVICE
ENGINE
SOON
A computer monitors operation of your fuel, ignition
and emission control systems. This light should come on
when the ignition is on, but the engine is not running, as
a check to show you it is working.
If it does not come on at all, have it fixed right away. If
it stays on, or it comes on while you are driving, the
computer is indicating that you have a problem. You
should take your vehicle in for service soon.