Chevrolet 2001 Impala Owner's Manual page 291

Be sure the posted octane is at least 87. If the octane is
less than 87, you may get a heavy knocking noise when
you drive. If it's bad enough, it can damage your engine.
If you're using fuel rated at 87 octane or higher and
you hear heavy knocking, your engine needs service.
But don't worry if you hear a little pinging noise when
you're accelerating or driving up a hill. That's normal,
and you don't have to buy a higher octane fuel to get
rid of pinging. It's the heavy, constant knock that means
you have a problem.
If your vehicle is certified to meet California Emission
Standards (indicated on the underhood emission control
label), it is designed to operate on fuels that meet
California specifications. If such fuels are not available
in states adopting California emissions standards,
your vehicle will operate satisfactorily on fuels meeting
federal specifications, but emission control system
performance may be affected.
6-4
The malfunction indicator lamp on your instrument
panel may turn on and/or your vehicle may fail a
-
smog check test. See "Malfunction Indicator Lamp"
in the Index. If this occurs, return to your authorized
Chevrolet dealer for diagnosis to determine the cause of
failure. In the event it is determined that the cause of the
condition is the type of fuels used, repairs may not be
covered by your warranty.
Some gasolines that are not reformulated for low
emissions may contain an octane
called methylcyclopentadienyl manganese tricarbonyl
(MMT); ask your service station operator whether or
not the fuel contains MMT. General Motors does not
recommend the use of such gasolines. If fuels containing
MMT are used, spark plug life may be reduced and your
emission control system performance may be affected.
The malfunction indicator lamp on your instrument
panel may turn on. If this occurs, return to your
authorized Chevrolet dealer for service.
-
enhancing additive