valve using a new O-ring. Lubricate the O-ring with
petroleum jelly or equivalent. Tighten the fitting to
35 Y (26 lb-ft).
18. Install the trailer hitch to the vehicle. Refer to
Trailer Hitch Platform Replacement in SI. Tighten
mounting nuts and bolts to 88 Y (65 lb-ft).
19. Connect the rear fuel line fitting at the tee
assembly using a new O-ring. Lubricate the O-ring
with petroleum jelly or equivalent. Tighten the
fitting to 35 Y (26 lb-ft).
20. Connect the high pressure shutoff valve solenoid
electrical connector.
21. Open all manual tank valves.
22. Refill CNG system and perform leak check. Refer
to CNG Tank Venting in SI.
23. Perform leak check at ALL CNG line and tank
connections using a commercially available
combustible gas detector. If a leak is found, verify
with a leak detection fluid such as Swagelok
Snoop® or equivalent liquid leak detector.

Page 6

April, 2016

Bulletin No.: 16-NA-121

24. If any leaks are found, correct as necessary, and
repeat leak check.
25. Install the Aft Tank Cover. Refer to CNG Tank
Cover Replacement - Aft Tank in SI.

CNG Tank Valve Replacement - Midship Tank
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 midship tank cover. Refer to CNG
Tank Cover Replacement - Midship Tank in SI.
While an assistant holds the shield in place,
remove the tank shield bolts only. Lower the shield
from the vehicle.

4484858

6. Disconnect the 2 lines and 1 hose (1) at the
midship tank valve.
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.

4484828

3. Remove the 2 nuts, bolts (1), and shield from the
cross member located forward of the midship tank.
4. Disconnect the electrical connector from the high
pressure shutoff valve solenoid.
5. Close the manual tank valve.

4477603

Bulletin No.: 16-NA-121

April, 2016

Valve removal/installation tool for LYRA CV type valve

7. 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.
8. Remove the valve, and inspect valve port threads
for damage or debris. Clean if necessary.
Caution: Refer to Fastener Caution in SI.
9. Install the prepared valve onto the tank using the
special tool. Torque to 128–133 Y (94 - 98 lb-ft.).

Page 7

19. If any leaks are found, correct as necessary, and
repeat leak check.
20. Install the midship tank cover. Refer to CNG Tank
Cover Replacement - Midship Tank in SI.

CNG Tank Valve Replacement - Cargo Tank
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.
3. Remove the cargo tank cover. Refer to CNG Tank
Cover Replacement - Cargo Tank in SI.

4484756

10. If needed. index and align the new valve to the
lines. Support the tank with a suitable jack. (Place
jack supports to allow tank straps to move freely.)
11. Secure tank to jack with non-marring webbing or
straps.
12. Loosen all 4 vehicle tank straps and rotate the tank
to the desired orientation for line attachments to
the valve.
• Torque the main tank strap fasteners to 42 Y
(30 lb-ft).
• Torque the PRD tank strap fasteners to 14
Y (10 lb-ft).
13. Install PRD vent lines to the new valve.
• Replace all O-rings with new seals.
• Lubricate the new O-rings with petroleum jelly
or equivalent before installation.
14. Tighten fittings to 35 Y (26 lb-ft).
15. Connect the high pressure shutoff valve solenoid
electrical connector.
16. Open all manual tank valves.
17. Refill CNG system and perform leak check. Refer
to CNG Tank Venting in SI.
18. Perform leak check at ALL CNG line and tank
connections using a commercially available
combustible gas detector. If a leak is found, verify
with a leak detection fluid such as Swagelok
Snoop® or equivalent liquid leak detector.

4484862

4. Remove the 3 fasteners (1) securing the rear part
of cover to the floor.
5. Gently pry/pull away and secure the rear part of the
cover to gain access to the cargo tank valve. Use
caution not to bend the front plane of cover.
6. Loosen the hose clamps securing the vapor bag to
the tank and underbody pass-through.
7. Disconnect the electrical connector from the high
pressure shutoff valve solenoid.
8. Disconnect the line at the 9 O' Clock position on
the cargo tank valve.
9. Remove the vapor bag from the valve assembly.
10. Close the manual tank valve.

Page 8

April, 2016

Bulletin No.: 16-NA-121

Valve removal/installation tool for LYRA CV type valve

4484865

11. Disconnect the remaining 2 lines (1) at the Cargo
tank valve.
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.

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. Install the new vapor bag and secure the lower
hose clamp.
16. Install the prepared valve onto the tank using the
special tool. Torque to 128–133 Y (94–98 lb-ft.).
17. If needed, loosen tank straps and rotate the tank to
the desired orientation for line attachments to the
valve.
• Torque the main tank strap fasteners to 42 Y
(30 lb-ft).
18. Install PRD vent lines to the new valve.
• Replace all O-rings with new seals.
• Lubricate the new O-rings with petroleum jelly
or equivalent before installation.
19. Install the high pressure fuel supply hose.
• Replace all O-rings with new seals.
• Lubricate the new O-rings with petroleum jelly
or equivalent before installation.
20. Tighten fittings to 35 Y (26 lb-ft).
21. Connect the high pressure shutoff valve solenoid
electrical connector.
22. Open all manual tank valves.
23. Refill CNG system and perform leak check. Refer
to CNG Tank Venting in SI.
24. Perform leak check at ALL CNG line and tank
connections using a commercially available
combustible gas detector. If a leak is found, verify
with a leak detection fluid such as Swagelok
Snoop® or equivalent liquid leak detector.
25. If any leaks are found, correct as necessary, and
repeat leak check.
26. Once it has been verified there are no leaks,
complete installation of the vapor bag, and all tank
covers and shields. Refer to CNG Tank Cover
Replacement - Cargo Tank and CNG Tank Cover
Replacement - Aft Tank in SI.

Parts Information
Description
Replacement Valve Kit includes valve and components
needed. Valve removal/installation tool on loaner program,
to be returned.

4477603

Bulletin No.: 16-NA-121

April, 2016

Warranty Information

Version

Labor
Operation

Description

Labor Time

4081188

Prep New Valve

0.2 hr

Add

Replace Aft Tank Valve

2.0 hrs

Add

Replace 2nd Aft Tank Valve

0.9 hr

Add

Replace Cargo Tank Valve

1.7 hrs

Add

Replace Midship Tank Valve

1.4 hrs

Add

CNG Tank Venting

0.8 hr

Page 9
1

Modified

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these
technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper
service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a
job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your
vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the
information.

WE SUPPORT VOLUNTARY
TECHNICIAN
CERTIFICATION