Maybe this will shed some light on the issue. Keep in mind that under warranty, only the malfunctioning side is fixed unless it's directly called out in the bulletin to do both sides.
Another tidbit of information which really applies to all models with wedge type bases, tail/stop/turn bulbs like 3057,3157, 3056, 3156, you get the idea I hope. These bulbs generate a fair amount of heat in them and sometimes people replace bulb after bulb thinking they have bad bulbs when really they have a bad socket. If you have the four ways on and the parking lights while you're checking the affected bulb for lets say stop/turn bulbs, take the socket out of the lamp and wiggle the bulb a little side to side, pull on it like you're pulling it out just a little then push it back in. If you notice the bulb working, then not working, you most likely have a bad socket.
Keep in mind the bulb will get hot fast and you can easily burn your fingers so use appropriate care. The socket overheats and the terminals spread a little and the connection in the socket is poor. Replace the affected socket and bulb and whae you replace the socket use a little, a dab 'll do ya of silicone dielectric grease on the base of the new bulb before you put it in. This helps to dissipate the heat some and will lead to longer socket life. Just a little FYI.
Here's the headlamp bulletin.
#10-08-42-001B: Low Beam Headlamp Bulb Diagnosis/Replacement (Inspect Bulb and Connector) - (Jan 24, 2011)
Subject: Low Beam Headlamp Bulb Diagnosis/Replacement (Inspect Bulb and Connector)
Models: 2008-2011 Buick Enclave
2007-2011 Cadillac Escalade, Escalade ESV, Escalade EXT
2008-2011 Cadillac CTS, CTS-V
2010-2011 Cadillac CTS Sport Wagon, SRX
2007-2011 Chevrolet Avalanche, Silverado, Suburban, Tahoe
2008-2011 Chevrolet Malibu
2009-2011 Chevrolet Traverse
2010-2011 Chevrolet Equinox
2007-2011 GMC Acadia, Sierra, Yukon, Yukon XL, Yukon Denali, Yukon Denali XL
2010-2011 GMC Terrain
2006-2010 Pontiac G6
2007-2010 Saturn AURA, OUTLOOK
Attention: This bulletin DOES NOT apply to vehicles equipped with High Intensity Discharge (HID) lamps.
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This bulletin is being revised to update the part number for the recommended splice sleeve. Please discard Corporate Bulletin Number 10-08-42-001A (Section 08 - Body and Accessories).
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Condition
Some customers may comment that the low beam headlamp is inoperative.
Correction
DO NOT replace the entire headlamp assembly for this condition.
Replace the bulb and inspect the connector following the procedure below.
Remove the headlamp bulb. Refer to Headlamp Bulb Replacement procedure in SI.
Inspect the connector.
• If the connector is NOT discolored or damaged, replace the bulb only. For bulb part numbers, see Headlamp Bulb (Low Beam) in Group 02.727 of the appropriate Parts Catalog.
• If the connector is discolored at the bulb interface, replace the connector (service pigtail listed below) and bulb.
Important: Use only Duraseal splice sleeves (salmon, P/N 19168446). Other splice sleeves may not protect the splice from moisture or provide a good electrical connection. Refer to Splicing Copper Wire Using Splice Sleeves in SI for splicing procedures.
1. Cut the wires of the connector approximately 45 mm (1¾ in) from the connector and splice in the service pigtail connector. Ensure that the splices are not above the connector when re-installing.
2. Replace the bulb.
Verify that the headlamp is fully functional.
Parts Information
Usage
Part Number
Description
CTS, SRX, Malibu, AURA, G6, Full-Size Trucks, Acadia, Enclave, Traverse, OUTLOOK
20939657
Cable (Connector) Assembly, Headlamp (Service Pigtail)
Equinox/Terrain
20938905
Connector Assembly, Headlamp Wiring Harness
OUTLOOK
20913209
Harness Assembly, Headlamp Wiring