freightliner M2 Plus 2023 Manual page 247

Pre- and Post-Trip Inspections and Maintenance
2.1 If not previously drained, drain the air
reservoirs using moderate brake
applications until pressure in both
reservoirs is less than 70 psi (483 kPa).
2.2 Turn the ignition to the ON position. The
ICU will complete a full gauge sweep and
bulb check, and a low-air warning buzzer
will sound. Ensure the low air pressure
lamp (BRAKE AIR) remains illuminated
and a low-air warning buzzer continues to
sound after the gauge sweep is complete.
3.
Check air governor cut-in and cut-out pressures.
3.1 Start the engine and ensure the BRAKE
AIR lamp goes out and the buzzer
silences when pressure reaches
approximately 70 psi (483 kPa) in both air
reservoirs.
The air governor should cut out at
approximately 120 psi (827 kPa). For
vehicles with an optional dryer reservoir
module (DRM), the cut-out pressure is
approximately 130 psi (896 kPa).
3.2
With the engine idling, apply the brake
pedal several times. The air governor
should cut in when pressure in the primary
air reservoir (top air gauge) reaches
approximately 100 psi (689 kPa).
4. Check air pressure build-up time.
4.1 With the air system fully charged, make
one full brake application and note the air
pressure reading on the primary air
gauge.
4.2 Further reduce air pressure using
moderate brake applications, then run the
engine at governed rpm.
4.3
Note the time that the pressure reaches
the previously noted reading on the
primary air gauge, then note the time that
the air pressure reaches cut-out pressure.
4.4 If it takes longer than 30 seconds to reach
cut-out pressure after the primary air
gauge passes the previously noted
pressure (noted after one full brake
application), eliminate any leaks or replace
the air compressor before operating the
vehicle.
5. Check air leakage in the system.
5.1 With the parking brake applied, the
transmission out of gear, and the air
system fully charged, release the service
brakes and shut down the engine.
5.2 Wait one minute and note the air pressure
drop in psi (kPa) per minute from the
primary air reservoir.
If the pressure drop exceeds the limits
shown in Table
before operating the vehicle.
6. Check the air pressure reserve.
With the engine still off, make one full brake
application and observe the pressure drop on the
primary air gauge. If pressure drops more than
25 psi (172 kPa), eliminate any leaks before
operating the vehicle.
Maximum Allowable Air Leakage
Description
Truck or Tractor Only
Truck or Tractor w/Single Trailer
Truck or Tractor w/Two Trailers
Table 22.1, Maximum Allowable Air Leakage
WARNING
When cleaning windshields and windows, always
stand on the ground or on a secure ladder or
platform. Use a long-handled window cleaner. Do
not use the cab steps, tires, fenders, fuel tanks,
engine, or under-hood components to access the
windshield or windows. Doing so could cause a
fall and result in an injury.
7. Inspect the mirrors, window glass, and
windshield for cracks or other damage.
8.
Ensure that the horn, windshield wipers, and
windshield washers are operating properly.
These devices must be in good working order for
safe vehicle operation.
9. Ensure the heater and defroster are operating
properly.
10. Check the operation of all interior lights.
10.1
Turn on the headlamps and leave them
on. If equipped, ensure all gauge bulbs
illuminate. If equipped, ensure ICU
screens illuminate.
22.1, eliminate any leaks
Pressure Drop:
psi (kPa) Per Minute
Released Applied
2 (14) 3 (21)
3 (21) 4 (28)
5 (35) 6 (42)
22.6