TM 5-2410-241-23-1
0008
ELECTRICAL SYSTEM CONTINUED
Solenoid Valve (Secondary Brake)
0008
The secondary brake solenoid is an ON/OFF type that is controlled by the secondary brake limit switch on the
brake pedal. This switch is activated when the brake pedal is fully depressed. The ECM also has an output
connection to the secondary brake solenoid. If the ECM detects a fully depressed pedal condition in the secondary
brake solenoid circuit, it will energize the solenoid in order to engage the service brakes.
When the brake pedal is completely depressed, the secondary brake limit switch will close and send +battery
power to the secondary brake solenoid. This will cause the service brakes to engage. This works independently of
the ECM. When the operator engages the parking brake, the ECM will also energize the secondary brake solenoid.
Solenoid Valve (Parking Brake)
0008
During normal operation, the ON/OFF type solenoid valve for the parking brake operates independently of the
ECM. Normally, the solenoid valve is energized by the parking brake switch. When the parking brake switch is in
the ON position, the solenoid valve is energized. This results in the hydraulic oil pressure being "dumped" away
from the brake actuator in order to engage (ON) the parking brake. When the parking brake switch is in the OFF
position, the solenoid is de-energized, the hydraulic oil pressure is allowed to flow to the parking brake actuator in
order to disengage (OFF) the parking brake.
The parking brake solenoid is also connected to an ECM output contact. When the parking brake switch is ON, the
signal at the ECM contact should measure 24 VDC. If the ECM determines that the signal is incorrect, the ECM will
activate a level 2 diagnostic code.
The ECM receives two inputs from the parking brake switch in order to determine the state of the switch. When the
ECM determines that the parking brake switch is in the ON position, the ECM will also energize the secondary
brake solenoid.
The parking brake state and the states of the three machine braking solenoids are indicated in the following table.
Table 5. Machine Solenoids.
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Parking Brake Switch
Parking Brake
ON
Switch OFF
(Engaged)
(Dis-engaged)
Proportional Brake
Not Active
Active
Solenoid
Secondary Brake
Active
Not Active
Solenoid
Park Brake Solenoid
Active
Not Active
