replacement from Gillig if necessary.
5. Use an 11/16-in. wrench to replace Manifilter
drain plug (2). Figure 28
Torque Manifilter drain plug to 26 ft-lbs
(35 Nm).

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4.7.2. Replacing the HP Fuel Filter Element
To replace the HP fuel filter element inside the
Manifilter:

1

1. Depressurize the system. Refer to Section 4.5.
2. Drain Manifilter. Refer to Section 4.7.1.
3. Unscrew Manifilter bowl (7) using a filter bowl
removal tool or a 1-1/4-in. wrench. Figure 29
4. Remove and replace old filter element (5). Figure
29
5.

6.

Apply a thin coat of lubricant (supplied
with element replacement kit) to element
housing O-ring (3) and filter bowl O-ring
(2). Figure 29
Lubricate Manifilter bowl (7) threads with
silicone lubricant. Figure 29
DO NOT allow silicone lube to contaminate filter
bowl or element.

4

3
5

6
2
7
Apply silicone
lube to
Manifilter bowl
threads

8
9

Figure 29. Manifilter components.
Manifilter housing (1), bowl O-ring (2), element O-ring (3),
element housing (4), HP filter element (5), housing base (6),
Manifilter bowl (7), drain plug O-ring (8), drain plug (9).

7. Reinstall Manifilter bowl (7). Figure 29
Tighten Manifilter bowl to 50±1 ft-lbs
(67.79±1.36 Nm).
Table 6. HP filter torque specifications.

Manifilter Torque Specifications

Component
Filter bowl
Hex head plug
Flow port fittings
(IN/OUT)

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ft-lbs
50±1
25-30

Nm
67.8±1.36
33.9-40.7

25-30

33.9-40.7

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4.8. Maintaining Low-Pressure Filter
4.8.1. Low-Pressure Filter Replacement and
Service
The low-pressure (LP) filter should be drained daily
and replaced every 12 months.

Tighten new LP filter housing by hand until
gasket contact is achieved, then turn the filter
housing another 3/4-turn.
Avoid cross threading.

Depending on fuel quality and characteristics, filter
drainage and replacement may be required more
frequently than the prescribed schedule.

4.8.2. Draining LP Filter and Replacing the LP
Filter Housing
1. Depressurize fuel system. Refer to Section 4.5.
2. Drain Manifilter. Figure 28. Refer to Section 4.7.1.
3. Drain LP filter housing by turning the drain cock
counterclockwise or until liquid begins to flow.
When the flow stops, turn drain cock clockwise
until fully seated hand tight. Figure 30

Figure 30. LP filter drain cock location.

4. To replace LP filter, remove LP filter housing by
turning it counterclockwise. This step may require
a strap wrench or grip pad. Dispose of the filter
housing per regulations. Figure 30
5. Install new LP filter. The filter gasket is lubricated
at the factory, no additional lubrication is required.
Figure 30

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4.9. Supply Solenoid Valve (SSV)
The supply solenoid valve (SSV) is a two-way valve
activated electrically by the ignition switch. By
default, it is in the “OFF/CLOSED” position. Figure
31

Supply solenoid valve coils are designed to operate
continuously for a lifecycle of 22,000 hours. Coils
generate significant heat and require adequate
open space for dispersion. When a coil remains
energized for extended periods of time the
assembly will be hot. Although the coil is designed
to operate under these conditions smoke or the
scent of burning coil insulation may be an
indication of overheating; in which case the coil
may need to be replaced.

Figure 31. Supply solenoid valve (1) location in FMM.

Problem

Table 7. Supply solenoid valve(SSV) troubleshooting.

Possible Causes / Items to Check

Check electrical supply with a voltmeter. Voltage
must match nameplate rating.

Valve fails to operate.

1. Check the electrical supply with a voltmeter.
Voltage must match nameplate rating.

Valve fails to operate.
Valve is sluggish or inoperative, but
there are no issues with power supply
and/or pressure

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2. Check coil with an ohmmeter for an open or short
condition.
3. Verify pressure complies with nameplate rating.
4. If no apparent system problem exists: remove and
replace the supply solenoid valve.

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4.10. Cylinders
CNG cylinders that have been involved in an
incident that registers at level 2 or 3 should be
depressurized prior to inspection.
Failure to perform regular or emergency
inspections may result serious injury or death.

4.10.1. Inspecting Cylinders
The composite containers on the vehicle are
manufactured to comply with FMVSS 304, NAI/IAS,
or the CSA B51 Part 2 specifications.
Cylinders must be inspected by a qualified cylinder
inspector every 3 years or 36,000 miles (58000 km),
whichever comes first.

The inspector should provide a report for each
cylinder and place an inspection label on each of the
cylinders. Containers must also have permanent
labels in accordance with applicable regulations.
These labels provide valuable information to both
the inspector and the manufacturer.
Cylinders must be inspected immediately if:
1. The vehicle has been in an accident.
2. The fuel container or vehicle has been subjected
to fire, impact, excessive, heat, or any other
means that may have caused external or internal
damage.
3. Unusual behavior is observed. This may include
but is not limited to, emission of natural gas odor,
unexpected loss of gas pressure, snapping or
hissing sounds, rattling, and any other indications
of loose parts.
4. The fuel tank has been transferred to another
vehicle or the tank installation has been altered
significantly.
5. Question system owner/operator about incidents
or conditions which may have caused damage to
the fuel container. These include but are not
limited to the following: dropping the container,
impacts, exposure to excessive heat, fire or harsh
chemicals
and
vehicle
accidents.
The
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owner/operator should keep records of any
unusual observations as well the service history
of the container and any repairs since the
container was last inspected.
4.10.2. Cylinder Venting Procedure
Before depressurizing a cylinder, ground the
venting orifice with a minimum 3-gauge wire to an
appropriate ground source at least 8-ft (2.44m)
underground. Rapid discharge can generate
enough static electricity to ignite escaping gas.

When venting a cylinder always do so in an open
area with good air circulation and no sources of
open flame, ignition, or heat. Do not vent the system
where flammable gas is permitted to accumulate
and potentially ignite. Refer to Section 5, “Defueling
Preparation and Procedures.”

4.11. Valve Maintenance
Valves do not require regular maintenance.
If a malfunction should occur, check for leaks first
and replace valve if necessary.

4.12. Pressure Relief Devices (PRDs)
The pressure relief devices used on this system
have been designed in accordance with ANSI-CSA
PRD-1 and meet or exceed the requirements for fuel
container pressure relief devices onboard natural
gas vehicles. Figure 21a and 21b
4.12.1. PRD Visual Inspection
PRDs do not have consumable parts and require no
additional maintenance other than visual inspection.
Figures 32, 33a, and 33b
PRDs must not have any aesthetic or structural
deficiencies.

Remove any visible contaminants, debris, and
moisture from the inlet port of the PRD. Figures 32,
33a, and 33b

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PRDs that do not pass visual inspection must be
replaced.

4.12.2. Draining Vent Lines
Refer to Figures 32, 33a, and 33b. PRD vent lines
have a drainage hole in the lowest point on the tube.
All vent lines should be checked for blockage during
component inspections to prevent water build-up
that can corrode the components. PRD vent lines
should be drained frequently on vehicles operating
in high humidity regions.

Verify lines to be loosened or removed are vent
lines and NOT fuel or PRD supply lines. Loosening
or removing a fuel line can result in serious injury
because it contains high-pressure gas.

The COMPRESSED FUEL line is the tubing that is
CLOSEST to the handle on the valve. If uncertain,
trace the line in question. If a line connects to a 3/4in. fuel supply line, it is a high-pressure fuel line and
should not be handled unless the system is
depressurized. If a line is open on one end with a
cap, it is a PRD vent line and is not under pressure.

If any PRD vent caps are missing, the vent tube
should be inspected immediately and new caps
installed.

PRD vent tubes are not under pressure; it is safe to
service the PRD vent cap.

1

1

1

1

Figure 32. System cylinder plug end with PRD vent lines (1) and PRD vent tube caps (circled).

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1

3

3

3

3

2

2

4

Figure 33a. System cylinder valve end—manual cylinder valve system, p/n 25530000.
Cylinder valve (1), high-pressure fuel tubes (2), live PRD tubes (3), fuel manifold (4).

Live PRD tubes always contain full system pressure.

2

3

3

5

6

4

1

Figure 33b. System cylinder valve end—electric solenoid cylinder valve system, p/n 25531000.
Cylinder valve (1), high-pressure fuel tubes (2), live PRD tubes (3), fuel manifold (4), pressure transducer (5), PRD manifold (6).

Live PRD tubes always contain full system pressure.

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4.13. Fill and Defuel Receptacles
4.13.1. Receptacle Maintenance

Receptacles connect to the FMM via straight
threads to female SAE ports.

Receptacle external surfaces must be kept clear of
contaminants and debris. Dust caps (4) and (5) are
provided to prevent debris intrusion and extend
system life. Figure 34

1

3

4.13.2. Transit (Fast) Fill Freeze-Up
Transit (fast) fill receptacles are prone to freezing
during rapid filling procedures due to “wet”
compressed natural gas conditions.

To remedy freeze-up, return FMM 1/4-turn manual
shutoff valve (2) to the “OFF/CLOSED” position until
external icing is no longer visible and the internal
poppet assembly achieves a seal. Figure 34
Once sealed, the check valve will resume normal
functionality and gas will cease to escape from the
receptacle.

2
4

5

Figure 34. FMM receptacles. Transit (fast) fill receptacle (1), 1/4turn manual shutoff valve (2), defuel receptacle (3), fast fill
receptacle dust cap (4) defuel receptacle dust cap (5). NOTE:
Smart Gauge equipped FMM face plate shown; non-Smart Gauge
face plate is similar.

External mounting hardware, receptacle O-rings
(not visible), and receptacle dust caps should be
checked periodically to ensure components are
functioning properly without leaks. Figure 34

The receptacle is to be used solely on a CNG
vehicle. The receptacle is designed to receive with
AGA/CGA NGV1 certified fueling nozzles. For
information
on
coupling
and
uncoupling
procedures, please consult detailed OEM
instructions provided with CNG fueling dispensers.

If component functionality is compromised or a leak
is detected, consult a qualified technician. Only
trained accredited personnel should service,
maintain, remove, or install a fueling receptacle.

The vehicle operator must not tamper, alter,
disconnect, or dissemble any receptacle or
component connected to a receptacle.
Installations shall be conducted in accordance with
regulations stipulated by the authorities having
jurisdiction (AHJ).

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5. Defueling Preparation and Procedures
A CNG vehicle may need to be defueled for maintenance or storage. The best and safest way to defuel a CNG
system is to transfer fuel back to a dispensing station, if so equipped. Check with CNG filling station for specific
procedures.

5.1. Basic Rules for Defueling

5.2.2. Compressor Transfer

1. Only CNG qualified personnel should attempt
these processes.

In this defueling method, a compressor at the fueling
station extracts fuel from the vehicle.

2. Consume as much fuel as possible prior to
defueling.

5.2.3. Return to Supply

3. Secure an approved place to put the fuel
removed from the vehicle.
4. Notify nearby personnel prior to defueling.
5. Always ground the vehicle and the fuel
system.
6. Never defuel indoors.

The third defueling method returns fuel to a
distribution system.
When using this process, pressure in the vehicle
tank and the supply system pressure will equalize
leaving pressure in the vehicle fuel system.

5.3. A Typical Venting Facility

7. Always wear appropriate PPE.
8. Be familiar with evacuation routes.

5.2. Defueling Requirements
CNG must be removed from the vehicle at an
approved facility.

The following information is provided in the absence
of formalized procedures from local authorities and
governing bodies. Figure 35 represents a typical
venting facility.

There are three common defueling options: vent to
atmosphere, compressor transfer, and return to
supply.

Venting CNG to atmosphere to requires care.
Improper equipment or procedures raise the risk of
fire.

In all cases, both the vehicle and the fueling system
must be grounded to prevent static electricity buildup.

Before depressurizing, ground venting orifice to an
approved electrical ground system.

5.2.1. Vent to Atmosphere
First, verify whether this method is legal. Local air
quality regulations may restrict the release of
methane into the atmosphere
If atmospheric venting is acceptable, a venting
facility compliant to regulations must be used.
Figure 35

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Always vent CNG in an open area with air circulation
and no nearby sources of open flame, ignition, or
heat.
Do not vent the system in an area where flammable
gas is permitted to accumulate and potentially
ignite.

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(Vehicle)

Vent stack/pipe
properly supported,
≥ 10-ft. (3m) above
ground

To rest of
fuel system
Defuel
receptacle

Electrically
conductive,
flexible hose

Defuel
nozzle

Bracket
Manual
valve