Vibration During Active Fuel Management V4 Mode Operation 1200 – 1400 Engine RPM – 2014-2015 Chevrolet Silverado & GMC Sierra

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Bulletin No.: PIP5228B Date: Dec-2015 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– 1400 Engine RPM Models: 2014-2015 Chevrolet Silverado 2014-2015 GMC Sierra equipped with 4.3L RPO LV3 This PI was superseded to update Recommendations/Instructions. Please discard PIP5228A. 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. 1 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. 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 If the above procedures do not correct the concern, check this document for updated repair information as engineering is aware of the concern and investigating. Parts Information Part Number Description Qty 20779889 Clamp, Exhaust Pipe 1 Warranty Information 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 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.

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