Solenoids can also be tested on a bench. Resistance
values are typically given in service manuals for each
application (Figure 40-10). A solenoid may be electrically
fine but still may fail mechanically or hydraulically. A
solenoid's check valve may fail to seat or the porting can be
plugged. This problem is not electrical; rather it could
be caused by the magnetic field collecting metal particles
in the ATF and clogging the port or check valve. These
would cause erratic shifting, no shift conditions, wrong
gear starts, no or limited passing (kickdown) gear,
or binding shifts. When a solenoid affected in this way is
activated, it will make
a slow dull thud. A good solenoid
tends to snap when activated.