Shift Solenoids - Hummer H1 Service Manual

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SHIFT SOLENOIDS

Two solenoids are used to control upshifts and downshifts in
the forward gear ranges. Solenoid A controls the 1-2 shift
valve while Solenoid B controls the 2-3 shift valve. Both sole-
noids are mounted on the valve body and operated by the
PCM.
The solenoids are energized or de-energized separately and in
combination to control shifts. The following chart outlines so-
lenoid activities in the various gear ranges.
Gear Range 1-2 Solenoid A
Park, Reverse, ON
Neutral
First ON
Second OFF
Third OFF
Fourth ON
The solenoids are de-energized when the PCM completes the
solenoid ground circuit. Incoming fluid passes around the
check ball and exits through the exhaust port (Figure 5-9). En-
ergizing the solenoid causes the coil to extend the plunger
blocking off the exhaust port. Incoming fluid is then routed
back to the 1-2 or 2-3 shift valve, overcomes spring pressure,
and moves the valve to required shift position.
An example of solenoid actuation is provided in Figure 5-10
which illustrates third gear flow. Solenoid A is de-energized
(off) causing signal A fluid to exhaust through the outlet port.
The 1-2 shift valve remains in position through normal valve
spring pressure. Energizing solenoid B, blocks the exhaust port
causing signal B and actuator feed pressure to act against the 2-
3 valve and spring. The two fluid pressures overcome spring
pressure moving the 2-3 valve into Upshift position. However,
in manual 1 and 2 ranges D21 fluid pressure prevents the 2-3
valve from moving to upshift position despite solenoid B ener-
gized state.
05745159
SIGNAL
FLUID
INLET
2-3 Solenoid B
PORT
OFF
OFF
OFF
ON
ON
Figure 5-10: Shift Solenoid Actuation (Third Gear
Transmission/Transfer Case
CONNECTOR
EXHAUST
PORT
O-RING
PLUNGER
METERING
BALL
Figure 5-9: Shift Solenoid Cross Section
Shown)
5-7
COIL
FRAME