Hexagon MT-45 User manual

DSM.0008 Ver 1.0 FCCC MT-45 / MT 55 CNG Diagnostics Service Manual
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Diagnostic Service Manual
Freightliner Custom Chassis Corporation (FCCC) MT
CNG Fuel Systems
FCCC Model Wheelbase
MT-45 168-in
MT-55 178-in
MT-55 208-in
DSM.0008 Ver. 1.0
February 24, 2022
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Preface FCCC MT CNG
This manual is designed as asupport document for trained technicians in the maintenance and diagnostic
procedures of the compressed gas fuel system provided by Hexagon Agility®.
No attempt shall be made to fill, install, maintain, or repair this system until this manual and all referenced supporting
documentation have been read and fully understood.
Original Equipment Manufacturer (OEM) replacement parts may be obtained by contacting Freightliner Customer
Chassis Corporation (FCCC).
Fuel system warranty or non-warranty product support may be obtained by calling or emailing Hexagon Agility®
Customer Care and Technical Services (CCTS).
Please provide your name, phone number, email address, and complete vehicle information:VIN, year,
make, model, mileage, unit number vehicle owner, and current vehicle location.Aservice advisor will contact
you to arrange vehicle repair or ship apart.
Do not remove components from original packaging until necessary. Any components
that are to be reinstalled must be thoroughly cleaned, inspected, and stored in a
satisfactory manner until reinstallation.
All replacement parts must adhere to the accepted standards and ratings as specified
by Hexagon Agility®. Use of any part that is not approved by Hexagon Agility®is not
recommended and may compromise the integrity and safety of the system.
Preface FCCC MT CNG

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Table of Contents FCCC MT CNG
Page
Preface 2
Acronyms 4
Safety 5
Warning and Signal Words Used in this Manual 5
Qualified Personnel 6
Safety Equipment 6
General Safety Precautions 7
Vehicle Fire Procedure 8
First Responder Guide 8
Codes and Compliances 8
Return to Service Inspection 8
Fuel System Schematic 9
Fuel System Troubleshooting and Diagnostics 11
Electrical 13
Connector Location View 13
Connector Pin-Out 15
Fuel Gauge Non-Operation 18
Crank, No-Start 36
No-Crank, No-Start 47
Engine Misfire Diagnostics 60
Fuel System Depressurization 69
Defueling 75
Filter Element Replacement 85
System Verification 95
Removal and Retightening of Tube Fittings (Appendix A. WI.0199) 96
Hexagon Agility® Customer Care and Technical Service 98

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Acronyms FCCC MT CNG
AGA American Gas Association HP high-pressure
ANSI American National Standards Institute IPC instrument panel cluster
ASM assembly LP low-pressure
Bar metric unit of pressure MIL malfunction indicator light
CGA Compressed Gas Association NFPA National Fire Protection Association
CNG compressed natural gas NGV natural gas vehicle
CSA Canadian Standards Association NSC National Standards of Canada
DMM digital multimeter OEM original equipment manufacturer
DS driver side PRD pressure relief device
ECM electronic control module PS passenger side
ECU electronic control unit psi pounds per square inch
FMI failure mode identifier SPN suspect parameter number
FMM fuel management module

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Safety FCCC MT CNG
Hexagon Agility® provides safety guidelines to ensure the safety of personnel servicing and / or operating
compressed natural gas (CNG) equipment. All personnel involved must adhere to the standards provided,
specialized training, along with federal, state, and municipal laws and regulations.
CNG presents unique characteristics that are distinctive from gasoline and diesel fuel. CNG when stored at ambient
temperature and 3600 psi (250 Bar) is in a gaseous state.
CNG vehicles are equipped with temperature activated pressure relief devices (PRDs) to evacuate stored fuel
safely in the event of a thermal event. PRDs trigger when cylinder(s) surroundings or internal enclosure
temperatures exceed 220°F (110°C) and use vent lines with dedicated exits to evacuate the pressurized gas. The
vent tube design allows for controlled evacuation/flaring under certain environmental conditions.
Hexagon Agility®minimizes these potential hazards through state-of-the art design and testing practices. Always
observe the procedures and recommendations of this manual.
Warning and Signal Words Used in this Manual
Symbol Definition
DANGER indicates a hazardous situation which, if not avoided, will result in death
or serious injury.
WARNING indicates a hazardous situation which, if not avoided, could result in
death or serious injury.
CAUTION indicates a hazardous situation which, if not avoided, could result in
minor or moderate injury.
NOTICE is used to address practices not related to physical injury, such as best
practices
or tips to help an operation or procedure go smoothly and prevent equipment
damage.
SAFETY INSTRUCTIONS indicate specific safety-related instructions or
procedures.
CRITICAL CHARACTERISTIC − Product feature directly affects:
Safety of vehicle users, people nearby and maintenance personnel, or
Regulatory compliance.
MANUFACTURING CHARACTERISTIC −
A product feature solely used to improve manufacturability or maintain process
control.
A process parameter or Step that has a significant effect on achieving a Critical
Characteristic or Significant Characteristic or maintaining material identification/
traceability.

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Safety FCCC MT CNG
Qualified Personnel
Safety Equipment
Individuals involved in any aspect of CNG fuel system maintenance, emergency
response, servicing or testing must be properly trained.Individuals who are not
trained are not permitted to service, maintain, test, or inspect asystem.
Observe all recommendations below when operating or servicing aCNG fuel system.
1. CNG safety signage should be visible at all applicable locations as stipulated by federal, state, and municipal
law.
2. Natural gas rated fire extinguishers should be accessible and visible throughout all servicing and fueling areas.
Verify fire extinguishers are charged, up to date, and rated correctly.
3. In case of emergency, self-contained breathing apparatus should be on site in an easily accessible area.
4. Areas designated for CNG fueling systems must have adequate lighting that complies with NFPA code.
5. Protective eyewear and footwear should be worn by all personnel near aCNG system.
6. When locating the source of aleak only use certified leak detecting solutions such as Swagelok Snoop®or
Formula 365 (p/n 10301242)or acombustible gas detector. Any other product or solutions are unacceptable.
7. Only use tools that are in good working order with proper calibration.
8. Wear appropriate attire and PPE while servicing or maintaining any CNG system.
Due to the presence of high-pressure and flammable fuel, CNG fuels systems are a form of hazardous energy
storage.
CNG systems must be maintained and inspected exclusively by trained personnel with qualifications in accordance
with the applicable codes.

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Safety FCCC MT CNG
General Safety Precautions
Observe all recommendations below when operating or servicing aCNG fuel system.
Strict compliance with proper safety and handling practices is essential when
operating aCNG fuel system.
1. Verify parking brake is engaged, wheels are chocked, and ignition switch is in OFF position.
2. Follow all maintenance procedures in the order in which they are written, do not skip steps unless with explicit
permission from Hexagon Agility®.
3. Never use an open flame as a source of illumination in proximity to a CNG system. Natural gas is both volatile
and explosive.
4. Any process or procedure that generates sparks, flames, or heated particles is never applicable in designated
CNG area.
5. If a CNG system does require a process or procedure that generates sparks, flames, or significant heat, refer
to ENP-442 for all Hot Work guidelines.
6. CNG fuel delivery systems are to be serviced in designated areas that comply will all federal, state, and
municipal laws and regulations.
7. When performing service or repairs to any portion of the fuel system, install proper lockout/tagout (LOTO)
device and observe all LOTO practices.
8. CNG servicing and fueling areas must be well ventilated as stipulated by federal, state, and municipal law.
9. Perform all maintenance and service procedures in a dust free environment.
10. Never attempt to open system components that are under pressure.
11. Never attempt to depressurize or vent a system by loosening a fitting.
12. A portable fire extinguisher rated for natural gas must be installed on the vehicle in an easily accessible
location.
13. Do not start engine if a CNG leak is detected.
14. Verify all systems are grounded before transferring CNG fuel from one vehicle to another. Transferring CNG
may cause a buildup of static electricity which could discharge and ignite the fuel.
15. Fuel system working pressure is up to 4500 psi (310.2 Bar). Hot weather fill pressures commonly reach 4100
psi (282.6 Bar).
16. Never smoke or produce an open flame near or around a CNG vehicle or a CNG dispensing/filling station.
17. Always ground vehicle prior to fueling or defueling.
18. If the vehicle will be out of service for an extended time, turn the 1/4-turn manual shut off valve to the
OFF/CLOSED” position. To consume residual CNG forward of the 1/4-turn manual shutoff valve run the
engine until it stalls.

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Safety FCCC MT CNG
First Responder Guide
For comprehensive emergency response procedures, refer to Hexagon Agility®
publication ENP-084,“First Responder Guide:CNG and LNG Vehicle Fuel Systems.”
Vehicles equipped with compressed natural gas must have blue reflective decals on the rear of the vehicle
identifying the fuel as CNG.
CNG blue diamond decal, Hexagon Agility®p/n 10602105
Blue diamond CNG decal cannot be installed on rear bumper per U.S. DOT mandate. Side CNG decals must be
installed adjacent to vehicle DOT number.
Codes and Compliances
For complete and detailed information concerning CNG codes and regulations please refer to the following:
USA: NFPA 52
Canada: CAN/CGA B109
North America: ANSI/AGA NGV 3.1 / CGA 12.3 and NGV 12.3-M95
In the event of aCNG fire it is imperative that the vehicle operator acts quickly and efficiently by observing the
following steps:
1. Turn off engine and set parking brake.
2. Get passengers out of vehicle as quickly as possible.
3. Evacuate the area.
4. Call 9-1-1.
5. Notify attending emergency personnel the vehicle is aCNG vehicle.
6. IF possible and only with the proper training:Extinguish fire using an appropriately rated fire extinguisher.
Vehicle Fire Procedure
Return to Service Inspection
If vehicle has been subjected to a fire or collision, the fuel storage system must be
inspected by aqualified inspector before it can be returned to service.

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FCCC Fuel System Schematics
Item Description
1fuel fill panel
2HP flexible fuel hose
31/4-turn manual shutoff valve
4high-pressure (HP) fuel filter
5pressure regulator
6* supply solenoid valve (SSV)
7low-pressure (LP) fuel tube
8LP fuel filter
9LP flexible fuel hose
10 fuel rails and fuel injectors
11† bleed valve
▬▬ LP fuel tubes
▬▬ HP fuel tubes
*part of pressure regulator assembly
†located on HP fuel filter
11
3
4
8
79
10
1
FRONT
Fuel Delivery System Schematic
2
65

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FCCC Fuel System Schematics
Fuel Storage System
Item Description
1cylinders
2cylinder manual valves
3PRDs
4* PRD adapters
*if equipped
Fuel Storage and PRD Vent System Schematics
2 2
1
1
3
FRONT
434
PRD Vent System
Item Description
APRD vent outlet (45°elbow)
B* PRD vent cap
▬▬ PRD vent tubes
*part of PRD vent outlet assembly
A
B

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Fuel System Troubleshooting and Diagnostics
The following section covers avariety of potential fuel system faults and their respective solutions.The conditions
addressed in this section are unique to CNG storage systems;however, conditions concerning other onboard
systems may influence or directly cause problems with the CNG storage system.
For any faults not addressed in this manual or for warranty information please contact Hexagon Agility®Customer
Care and Technical Services:
833-4-HEX-CARE, toll-free in the U.S. and Canada
CONDITION: After disconnecting the fuel fill nozzle, CNG flows out of the fill receptacle.
Issue Solution
Fuel fill receptacle O-ring frozen due to gas
expansion
•Close cylinder manual valve(s).
•Wait for receptacle to warm to ambient temperature to check if leak
persists.
•Use a slow fill rate to avoid icing.
Damaged fuel fill receptacle O-ring •Close cylinder manual valve(s).
•Replace O-ring.
Debris in fuel fill receptacle
•Close cylinder manual valve(s).
•Inspect exterior of fuel fill receptacle for blockage or damage.
•If no debris is found, fuel fill receptacle must be removed for internal
inspection.
Damaged fuel fill receptacle –external
evidence •Close cylinder manual valve(s).
•Depressurize fuel system.
•Replace fuel fill receptacle.
NOTE: inspect fill panel check valve when performing this repair.
Damaged fuel fill receptacle –internal check
valve failure
CONDITION: With the 1/4-turn manual shutoff valve in the closed position and the vehicle continues to run
for an extended period, suspect 1/4-turn manual valve fault.
Issue Solution
Valve seat wear / debris in valve does not
allow valve to fully close
•Close cylinder manual valve(s).
•Depressurize fuel system.
•Replace 1/4-turn manual shutoff valve.

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Fuel System Troubleshooting and Diagnostics
ISSUE: Poor engine performance (rough idle, lacks power, hesitation, stalls)
Issue Remedy
Low pressure side of fuel system is less than
125 psi (8.62 Bar)
•LP fuel hose restriction
•LP fuel filter clogged
•HP fuel filter clogged
•HP / LP fuel tubes kinked/bent
•pressure regulator fault
•fuel injector(s) fault
•Refer to Engine Misfire Diagnostic procedure section(s) below.
•Ignition system fault
•Induction system restriction
•Exhaust system restriction
•Mechanical engine failures
•Engine sensor fault
•Refer to OEM procedure.

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J3 OEM ECU connector located at (DS)
radiator core support. Refer to OEM
manual for pin-out.
C1 Electronic Control Module (ECM)
connector located inside at driver footwell.
C2 Electronic Control Module (ECM)
connector located inside at driver footwell.
IO31 Start Confirm connector located
behind instrument cluster.
IO30 Crank Request connector located
behind instrument cluster.
24
15
Electrical
Connector Location View
3
4
2
1
3910
11
8
5
7
612

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G21 Supply Solenoid Ground located
on frame between pressure regulator and
1/4-turn manual shutoff valve.
P31 Pressure Transducer connector
located on pressure regulator.
Y41 Supply Solenoid connector located
on pressure regulator.
G20 Fill Panel Ground located on
bottom of fill panel.
D81 DAP (Drive Away Protection)
located on bottom of fill panel.
F78 Fuel System Harness Interface
located near last crossmember of
chassis.
F79 Connector OEM Fuel Send and
Return Harness
Connector Location View
6
8
7
9
11
10
Electrical
12 AD
C
B

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Cavity Circuit Color Description
1409 BRN Low Reference
2604 RED 5V Reference
3 - - NA
4316 GRY Pressure Signal
1
4
2
ECM C2 connector pin-out
IO31 Start Confirm pin-out
Cavity Circuit Color Description
A313 PUR Start Relay Confirm A
Electrical
9
27
6
38




10 14 15 16
Cavity Circuit Color Description
1 - - NA
2313 PUR Start Relay Confirm
3314 BLU Start Relay Request
4 - - NA
5 - - NA
6204 PNK Supply Solenoid (B+)
7312 GRN Drive Away Protection
8204 PNK ECM Power
9408 TAN Fuel Gauge Low Reference
10 315 WHT Fuel Gauge Signal
11 - - NA
12 - - NA
13 - - NA
14 312 GRN Drive Away Protection
15 312 GRN Drive Away Protection
16 104 BLK ECM Ground
ECM C1 connector pin-out

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Cavity Circuit Color Description
1409 BRN Low Reference
2316 GRY Pressure Signal
3604 RED 5V Reference
1
2
3
P31 connector pin-out
Cavity Circuit Color Description
A409 BLUE Low Reference
IO30 Crank Request
A
Electrical
Cavity Circuit Color Description
A105 BLK Supply Solenoid Ground
G21 Supply Solenoid Ground
Cavity Circuit Color Description
A104 BLK ECM Ground
G20 Fill Panel Ground
Cavity Circuit Color Description
1204 PNK Supply Solenoid B+
2105 BLK Supply Solenoid Ground
Y41 Supply Solenoid
1
2

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AD
Cavity Circuit Color Description
A312 GRN Drive Away Protection
D81 DAP Drive Away Protection
Cavity Circuit Color Description
A104 BLK Supply Solenoid Ground
B315 WHT Fuel Gauge Signal
C406 TAN Fuel Gauge Low Reference
D204 PNK ECU Power
F78 Fuel System Harness Interface
A
A
D C B
Electrical
Cavity Circuit Color Description
A104 BLK Supply Solenoid Ground
B315 PK/WT Fuel Gauge Signal
C406 PK/WT Fuel Gauge Low Reference
D204 PK/WT ECU Power
F79 Connector OEM Fuel Send and Return Harness
C
B

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Fuel Gauge Non-operation
Fuel Gauge Non-operation
Fuel gauge non-operation occurs when the gauge displays empty while pressure greater than 600 psi(41.3 Bar) is
indicated on the HP fuel gauge.
Possible causes include the following:
1. Power or ground insufficient at pressure transducer
2. Power or ground insufficient on connector for ECM
3. Calibration or bad OEM ECU
The following diagnostic steps are designed to systematically identify the root cause(s) of non-operation fuel gauge
condition and point to corresponding repair procedures.
Symptom Description
To confirm this condition, ignition ON. The instrument panel cluster (IPC) will
perform self-check mode.If the fuel gauge needle sweeps to full and returns to
empty, the fuel gauge non-operation condition exists.

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Fuel Gauge Non-operation
The Electronic Control Module (ECM) monitors CNG fuel system pressure using apressure transducer in the
pressure regulator.The transducer monitors cylinder pressure using a 5V signal communicated to the ECM. The
ECM uses calibration logic to transmit resistance values via the F78-F79 connector interface.The OEM ECU
transmits fuel level through the CAN network to the IPC.
Circuit / Sensor Description
SPN: 96
FMI: 2,3,4,7
FMI 2: Fuel Level Sensor “A” Circuit Intermittent
FMI 3: Fuel Level Sensor “A” Circuit High
FMI 4: Fuel Level Sensor “A” Circuit Low
FMI 7: Fuel Level Sensor “A” Circuit Range / Performance
Fault Codes
The following fault code(s) may set when vehicle ignition is left in the ON position while the driver does not engage
the starter within approximately 30 seconds.
SPN FMI Type MIL Possible Faults
96 02 B Yes
•Vehicle was left with Ignition On, Engine off for a prolonged period.
•Malfunctioning ECM.
•Intermittent poor electrical connection.
•Damaged pressure transducer.
96 03 B Yes
•Vehicle was left with Ignition On, Engine Off for a prolonged period.
•Malfunctioning ECM.
•Reference circuit shorted to power.
•Open in signal circuit.
•Damaged pressure transducer.
96 04 B Yes
•Vehicle was left with Ignition On, Engine Off for a prolonged period.
•Malfunction in the ECM.
•Short to ground in the signal circuit.
•Short to ground in the low reference circuit.
•Loose electrical connector or terminal.
•Loose electrical connector or terminal.
96 07 B Yes
•Vehicle was left with Ignition On, Engine Off for a prolonged period.
•Malfunction in the ECM.
•Intermittent or poor connection.
•Damaged pressure transducer.

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Fuel Gauge Non-operation
ALWAYS use personal protective equipment (PPE) when working around
pressurized fuel systems.
Verify parking brake is engaged, wheels are chocked, and ignition switch is in
OFF position.
Tools and Supplies
General Safety Precautions
Item Purpose
safety glasses eye protection
shop rags clean fuel system components before and after repair
flashlight illuminate components
mirror observe backside of fittings while performing leak check
digital multi-meter (DMM) resistance and voltage measurements
PSI PowerLink or other
OBD-II diagnostic tool read fault codes and ECM values
Install proper lockout/tagout (LOTO) device and observe all LOTO practices.