[HUMTECH]

Subject: Popping/Snapping Noise When Vehicle is Hot, at Idle, or Immediately After Vehicle is Shut Off (Replace Muffler Heat Shield) #03-06-05-008C - (10/28/2005)



Models: 2002-2005 Cadillac Escalade, Escalade EXT

2003-2005 Cadillac Escalade ESV

2002-2005 Chevrolet Avalanche, Suburban, Tahoe, Silverado, Silverado HD

2002-2005 GMC Yukon, Yukon Denali, Yukon Denali XL, Sierra, Sierra HD

2003-2005 HUMMER H2

with 4.8L, 5.3L, 6.0L , 8.1L Gasoline Engine (VINs N, U, T, V, Z, G -- RPOs LQ9, LQ4, LM7, LR4, L59, L18 )



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This bulletin is being revised to include Pickup models, 8.1L engines and parts availability. Please discard Corporate Bulletin Number 03-06-05-008B (Section 06 -- Engine/Propulsion System).


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Condition
Some customers may comment on a popping/snapping noise from underneath the vehicle at idle or immediately after the vehicle is shut off. Some popping/snapping noise from the exhaust system during cool down is a normal condition.

The noise may be intermittent depending on the outside temperature and or temperature of the exhaust system at the time of testing.

Cause
As the exhaust system warms and cools, the muffler and the muffler heat shield expand and contract at different rates and may cause a popping and/or snapping noise.

Some popping/snapping noise from the exhaust system during cool down is a normal condition. The customer should be made aware that this service procedure is designed to reduce but not eliminate all exhaust system popping and snapping during cool down.

Correction
DO THIS
DON'T DO THIS

Install a new heat shield and straps on the existing muffler.
DO NOT replace exhaust system components other than the muffler heat shield.


Follow the service procedure below to correct this condition.

Important: Some popping/snapping noise from the exhaust system during cool down is a normal condition. The customer should be made aware that this service procedure is designed to reduce but not eliminate all exhaust system popping and snapping during cool down.

Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information (SI Document ID #737171).
Caution:

• In order to avoid being burned, do not service the exhaust system while it is still hot. Service the system when it is cool.

• Always wear protective goggles and gloves when removing exhaust parts as falling rust and sharp edges could result in serious personal injury.


Remove the nuts securing the muffler to the catalytic converter.
On 6.0L and 8.1L equipped vehicles only, loosen the exhaust pipe clamp.
Important: Do not use oil base lubricants on the rubber exhaust hangers.

Apply a soapy solution to the exhaust pipe hanger rods in order to ease the removal of the exhaust hangers.
Pry the exhaust hangers free from the exhaust pipe hanger rods.
Important: It is not necessary to remove the muffler from the vehicle to replace the muffler heat shield.

Reposition the muffler to gain access to the muffler heat shield.



Notice: Use extreme caution not to damage the muffler when removing the heat shield from the muffler.

Using an air-powered hack saw blade, or equivalent, cut off the existing muffler heat shield just as the heat shield rises off of the muffler. See the illustration above.
Remove the heat shield from the muffler.
Hammer flush the remaining heat shield to the muffler.



Important:

• The new heat shield should not come in contact with the remaining muffler heat shield.

• The new heat shield should not come in contact with the horizontal lock seam on the muffler.


Install the new heat shield (see parts list below) onto the muffler as shown above.



Install three straps, P/N 10391259, so that the strap screw head will be located on top of the muffler.
Tighten

Tighten the strap screw to 4 N·m (35 lb in).





Cut off the excess strap material and bend the strap over the strap screw head as indicated above.
Remove the exhaust pipe clamp.
Important: ONLY 6.0L and 8.1L equipped vehicles require a new exhaust pipe clamp, P/N 15103174.

On 6.0L and 8.1L equipped vehicles only, install a new exhaust pipe clamp, P/N 15103174, on the exhaust pipe.
Reposition the muffler in the correct position.
Slide the muffler forward into position, aligning the studs with the rear of the catalytic converter.
Install the nuts securing the muffler to the catalytic converter, but DO NOT tighten at this time.
Apply a soapy solution to the following areas in order to ease the installation of the hangers.
• The inner diameter of the exhaust pipe hanger

• The exhaust pipe hanger rod

Press the exhaust pipe hangers over the exhaust pipe hanger rods.
Tighten

• Tighten the muffler nuts by hand until each contacts the metal flange.

• Tighten the muffler nuts to 45 N·m (33 lb ft).

• On 6.0L and 8.1L equipped vehicles only, tighten the exhaust clamp to 50 N·m (36 lb ft).

Lower the vehicle.
Parts Information
Part Number
Description
Qty

15253526
Shield, Muffler Heat Shield

(24 inch shield)

with 4.8L or 5.3L engine

1500 Series Base Utility Trucks ONLY
1

10393433
Shield, Muffler Heat Shield

28 inch shield

with 6.0L engine (LQ4, LQ9)

H2 or 1500 Series Luxury Utility Trucks ONLY
1

15808181
Shield, Muffler Heat Shield

25 inch shield

with 6.0L or 8.1L engine (LQ4, LQ9, L18)

2500 Series Utility, HD Pickups and Luxury Pickup Trucks ONLY
1

15103174
Clamp, Exhaust Pipe

with 6.0L or 8.1L engines ONLY
1

10391259
Strap, Muffler Heat Shield Strap

All Vehicles
3

15103184
Clamp, Exhaust Pipe

(pipe size 2.75")

(25 Series Suburbans/Avalanche and 8600 lb. 25 Series Pickups w/LQ4)
1

15102680
Clamp, Exhaust Pipe

(pipe size 3")

(25 & 35 HD Pickups w/LQ4 or L18 engines)
1


Warranty Information
For vehicles repaired under warranty, use:

Labor Operation
Description
Labor Time

L2540
Shield, Muffler Heat Shield - Replace
0.8 hr




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.
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Document ID# 1719122
2003 HUMMER H2