Bulletin No.: PIP5228A
Date: Oct-2014

Subject:

Vibration During Active Fuel Management V4 Mode Operation 1200 – 1400 Engine RPM

Models:

2014-2015 Chevrolet Silverado
2014-2015 GMC Sierra
equipped with 4.3L RPO LV3

This PI was superseded to update Cab Mount Settling Procedure. Please discard PIP5228.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern
Some customers may comment about a vibration that is felt between 1200 – 1400 engine RPM when in active fuel management V4 mode. A drone or
resonance may also accompany this vibration. The vibration may occur at different vehicle speeds but the engine speed will be in the 1200-1400 RPM range.
This vibration does not occur in V6 mode.

Recommendation/Instructions
The technician should evaluate the vehicle under the conditions the customer duplicates the concern. Once the concern is duplicated, use a vibration analysis
tool, J 38792-A Electronic Vibration Analyzer 2 (EVA) or CH 51450-NVH Pico Oscilloscope Diagnostic Kit (w/NVH) to measure the frequency of the vibration. If
the measured vibration is not 23 Hertz (HZ), first order engine, use normal vibration diagnostics to isolate the source of the vibration. If the measured vibration
is 23 Hertz (HZ), first order engine, follow the three-way catalytic converter and cab mount settling procedures below

Three-Way Catalytic Converter Assembly Settling Procedure
Note: Do NOT replace the three-way catalytic converter assembly unless it is physically damaged.
Loosen the six nuts that fasten the three-way catalytic converter assembly to the exhaust manifolds.
Remove and replace the exhaust muffler clamp that joins the three-way catalytic converter assembly to the pipe of the muffler assembly. Note: This is a special
clamp called a Norma clamp and it must be replaced as it is a one time use clamp.
Reinstall the three-way catalytic converter assembly following the specific tightening sequence and fastener torque specifications found in SI.

Cab Mount Settling Procedure
Warning: When settling the body cushions, do NOT separate the frame from the body more than is necessary. Possible personal injury and
damage to multiple parts may result if you do not follow the guides outlined below:
Intermediate steering shaft—Do not allow the shaft to extend more than 25 mm (1 in).
Fuel tank filler hose—Do not stretch the hose excessively.
Tail/Turn signal lamp wiring/rear lamps junction block—Leave slack in the wires
Park brake cable—Leave slack in the cable.
Body ground straps—Leave slack in the wire
The technician should first loosen the fastener located at the center of each body mount (6 for a regular cab, 8 for crew and double cab).
Using a large angled pry bar, lift up the cab body slightly to settle / relax it. Perform this at each mount location one at a time.
Repeat this cab mount settling process twice, to confirm the mounts are settled / relaxed.
Visually verify that the cab to box alignment is correct before re-torquing all mounts to specification found in Service Information, body repair, frame and under
body section.

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The cab / body mount position locations
The numbers in the picture below indicate the specific mount position. The mounts on the passenger side of the vehicle are identified the same way. This will
assist the technician to identify the correct location of each mount so they can be torque to the proper specification.

1 = body mount cushion front
2 = body mount cushion position number 1
3 = body mount cushion position number 2
4 = body mount cushion position number 3

Parts Information
Part Number

Description

Qty

20779889

Clamp, Exhaust Pipe

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Labor Operation

Description

Labor Time

4050272

Exhaust System Alignment

Use Published Labor Operation Time

1431160

Body Mount Upper and Lower Cushion Replacement

Use Published Labor Operation Time

Warranty Information

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the
remaining steps do not need to be performed.
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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