Subaru 1998 Forester Owner's Manual page 160

The 1990 Clean Air Act Amendments require the Environmental Protec-
tion Agency (EPA) to implement programs to reduce air pollution from
motor vehicles. States are required to adopt either a "basic" or
"enhanced" vehicle Inspection/Maintenance (I/M) Program depending
on the severity of their air pollution problem. The "enhanced" I/M test
simulates actual driving conditions on a dynamometer and permits more
accurate measurement of tailpipe emissions than the "basic" I/M test
which measures emissions only during engine operating conditions at
idle and 2,500 RPM. The "enhanced" I/M test also includes a pressure
check to identify evaporative emissions leaks in the fuel system.
The U.S. EPA has EXEMPTED SUBARU Full-Time All-Wheel Drive (AWD)
vehicles from the following performance warranty short tests:
D Loaded Test
D Idle Test With Loaded Preconditioning
State I/M Programs should test affected SUBARU AWD models using
any other EPA-91 approved performance warranty short test. SUBARU
models equipped with the AWD feature should be tested on a four-wheel
drive dynamometer or the State I/M Program may elect to use a "double
two-wheel dynamometer" arrangement. Under no circumstances should
the rear wheels be jacked off the ground, nor should the driveshaft be
disconnected for I/M testing.
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