File in Section:

Service Bulletin

-

Bulletin No.:

16-NA-121

Date:

April, 2016

TECHNICAL
Subject:

Compressed Natural Gas (CNG) Valve Outgassing at Extreme Cold Temperatures

Attention: This Bulletin applies to any of the listed models equipped with RPO LC8.
Brand:

Model:

Chevrolet,
GMC

Express,
Savana

Model Year:

VIN:

from

to

2011

2016

from

to

Engine:
All

Transmission:

All

Condition

Some customers may comment that CNG gas is venting, leaking, or releasing during
extreme cold temperatures and/or during refueling.
During the early stages of a CNG fast-fill event, gas moves rapidly from the dispenser
(high pressure) into the vehicle’s fuel tank (low pressure). The gas cools rapidly when it
expands into the tank.
When a fast-fill occurs during cold ambient temperatures (−4°F or −20°C), portions of the
fuel tank valve in contact with the expanding gas may hit temperatures below −40°F or
−40°C. If the temperature remains below −40°F or −40°C for a period of time, CNG
leakage to the atmosphere can occur past an O-ring internal to the tank valve.
This is due to the O-ring losing its elasticity at these low temperatures.
As more gas enters the tank, its pressure increases and heat is generated during
recompression, thereby elevating the tank's internal temperature. The fuel tank valve
temperature will rise due to the heat of recompression. When the temperature rises
above −40°F or −40°C via recompression or by moving the vehicle to a warmer
environment, leakage past the O-ring will stop as elasticity is returned.
This scenario can be aggravated by fast-fills completed with dispensers not operating to
industry standard. By standard, dispensers should supply gas at pressure no more than
1.25 times the vehicle’s fuel tank service pressure. Higher initial dispensing pressures
can cause lower temperatures during gas expansion.

Cause

Cold temperatures along with the cooling effects of the refueling process causes the CNG
to leak through the valve, causing it to vent.

Additional Options

LC8 & FHZ & UFP & UFM, including C69 & C36

Correction
1. Verify the condition.
2. Verify the filling station is operating within
specifications.
3. Replace the vehicle tank valve with an updated
valve with new part number. Follow SI procedures.

Information
Note: If a customer exhibits a leak during the
conditions described, the filling station should be
verified for proper operation according to the above
specifications. If a leak is still present after verification
the technician should contact technical assistance for
more information and inquire about special tool.

Copyright 2016 General Motors LLC. All Rights Reserved.

The standards for CNG dispensing equipment are as
follows:
• ANSI/IAS NGV 4.1-1999 / CSA 12.5-M99 AMERICAN NATIONAL STANDARD/ CSA
STANDARD FOR NGV DISPENSING SYSTEMS
• NFPA 52 – Vehicular Gaseous Fuel
Systems Code
Warning: Natural gas is highly flammable. In order
to reduce the risk of fire and personal injury, keep
sparks, flames, and smoking materials away from
the vehicle while you perform the Compressed
Natural Gas (CNG) fuel system service. The
Compressed Natural Gas (CNG) system operates at
pressures up to 24820 kpa (3600 psi). Relieve the
CNG fuel system pressure before servicing CNG
fuel system components in order to reduce the risk
of fire and personal injury. Any CNG fuel tank which
is past its expiration date must be removed from

Page 2

April, 2016

service. Failure to follow these precautions may
cause personal injury or death, and/or damage to
the vehicle or its components.

Bulletin No.: 16-NA-121

Once all components are accounted for, follow the
procedure outlined below:

Service Procedure
Replacement Tank Valve Preparation
The following information should be used to prepare
each valve assembly for installation to the tank. Please
follow directions carefully. Additional instructions may
be included with the replacement valve.
Once you receive the new valve, the following
components will be in the box:
• Black O-ring
• Installation instructions
• OMB Lyra CV valve
• O-ring placement cap
• Solenoid cable
• White snap ring
4484717

OMB Lyra CV valve with white snap ring

4477603

Valve removal/installation tool for LYRA CV type valve

The Valve Removal/Installation tool is also provided.
4484719

Bulletin No.: 16-NA-121

April, 2016

OMB Lyra CV valve stem (1) with O-ring (2)
and snap ring (3) in place over threads (4)
1. Install the white snap ring over the threaded stem
of the valve such that the ridge is oriented down,
and it snaps securely into the groove outside of the
O-ring as shown.

Page 3

OMB Lyra CV valve with O-ring placement cap (1)
covering threads of valve stem, and O-ring lubricant

5. For ease of O-ring installation and protection,
install the supplied cap (1) over the valve stem
threads to ensure that the new O-ring is not
damaged during installation on the valve threads.
Lubricate the new valve O-ring with Molykote 55
O-ring lubricant (or equivalent), and install onto the
threaded stem of valve as shown. Use caution not
to damage or twist the O-ring. Ensure the O-ring is
fully installed and seated.

4484732

OMB Lyra CV valve threaded stem (1)
2. Inspect valve port threads for damage or debris.
3. Clean threads and O-ring groove on valve as
required with a clean lint-free shop cloth and
isopropyl alcohol. (Only the supplied O-ring in the
OMB kit with the new valve should be used when
installing a Lyra CV valve).
4. Dry threads and O-ring groove thoroughly with a
clean lint-free cloth. Make sure threads and O-ring
sealing surfaces are clean, dry, and free of
contaminants.

4484741

OMB Lyra CV valve with O-ring placement cap and lubricated
O-ring ready to be installed, white snap ring already installed

4484743

Guiding O-ring down over cap to flat surface
6. Press the lubricated O-ring down over the cap until
it sits flat on the surface as illustrated.
4484737

Page 4

April, 2016

4484746

OMB Lyra CV valve with O-ring successfully seated

Bulletin No.: 16-NA-121

4484753

3. Close the manual tank valves (1).
4. Remove the trailer hitch. Refer to Trailer Hitch
Platform Replacement in SI.
5. Disconnect the high pressure shutoff valve
solenoid electrical connection.
6. Disconnect the rear fuel line fitting at the tee
assembly.
Note: Take note of all fitting and plugs on each valve
and transfer to the new valve as necessary ensuring
they are transferred to the same, correct location on the
new valves.

4484749

Removing the O-ring placement cap
7. Remove the O-ring placement cap from the valve.

CNG Tank Valve Replacement - Aft Tanks
Danger: To reduce the risk of explosion and fire, or
asphyxiation from compressed natural gas (CNG),
which if not avoided will result in death or serious
injury and property damage:
– Always reject valves or fuel tanks with damaged
threads and/or damaged O-rings.
– Reject fuel tanks with O-ring groove damage since
these damages prevent a safe and effective seal.
Failure to follow the procedures exactly as written
may result in serious injury or death.
1. Vent all CNG fuel tanks. Refer to CNG Tank
Venting in SI.
2. Remove the Aft Tank Cover. Refer to CNG Tank
Cover Replacement - Aft Tank in SI.

4484777

7. Carefully disconnect all lines and hoses from tank
valve being replaced, noting location and
positioning of lines prior to removing. There are 4
connections (1) on the forward aft tank valve, and 3
connections (2) on the rear aft tank valve.

Bulletin No.: 16-NA-121

April, 2016

4484756

8. Support the appropriate tank with a suitable jack.
(Place jack supports to allow tank straps to move
freely.)
9. Secure tank to jack with non-marring webbing or
straps.
10. Loosen vehicle tank strap fasteners.
11. Reposition/shift tank toward passenger side to
allow clearance for valve removal tool.
Note: Take note of the clocked position of the valve,
the location of all fittings, and plugs. The new valve
must be in the same clocked position, as well as
transferring all fittings and plugs to the same correct
location on the new valve.
Warning: A large release of gas would require you
tighten valve and follow venting procedures again.
It is however NOT uncommon to have a short 30
second vent of residual gasses release, this is
normal and will cause no harm. If there is no
gaseous release, proceed to unscrew the tank valve
by hand until free from the CNG tank. Failure to
follow these precautions may cause personal injury
or death, and/or damage to the vehicle or its
components.

Page 5

4477603

Valve removal/installation tool for LYRA CV type valve
12. Use the ½” drive special tool to remove the valve
from the tank. (Tool is indexed to the valve to fit
one way.) Break the valve free, and loosen slowly,
listening for high pressure release.
13. Remove the valve, and inspect valve port threads
for damage or debris. Clean if necessary.
Caution: Refer to Fastener Caution in SI.
14. Install the prepared valve onto the tank using the
special tool. Torque to 128–133 Y (94–98 lb-ft.).
15. Reposition the tank and valve assembly. Rotate
the tank to the desired orientation for line
attachments to valve. Torque strap fasteners to 40
Y (30 lb ft).
16. Install PRD vent lines to the new valve. Replace all
O-rings with new seals. Lubricate new O-rings with
petroleum jelly or equivalent before installation.
Tighten fittings to 35 Y (26 lb-ft).
17. Connect the rear fuel flex line fitting at the tank