2004.5-2005 GMC Duramax LLY Air Filters

Filters and the 2004.5-2005 GMC LLY

A Sierra SLT with a camper on the back and a plugged air filter will tell you about it on the first long grade. The element in the fender airbox is the first restriction the compressor sees, and the factory mouthpiece behind it is the second. GM's inlet is restrictive enough that the LBZ-style horn fitted for 2006 cut peak-flow restriction from roughly 15-20 inHg to 8-10 inHg; a loaded filter pushes the stock number the wrong direction. Keeping the element clean is the one intake decision that costs almost nothing and affects every mile.

What goes wrong

The failure is restriction, and the symptom set is borrowed from the turbo: lazy spool, EGT that climbs faster than the load, a truck that feels tired at highway speed with a trailer. BD Diesel's diagnostic order for suspected vane sticking begins with boost leaks and intake or filter restriction, because a dirty element produces the same complaint and is a fraction of the cost to rule out. On sand, shell roads and ag ground the element loads well ahead of any mileage schedule. Separately, the inside of the intake tract collects EGR soot and PCV oil over time; that is a Y-bridge cleaning job, not a filter problem, and no element will stop it.

Choosing a filter

Start with what intake the Sierra has. Factory airbox: a 2001-2005 Duramax drop-in element. S&B cold air intake: an S&B KF-series replacement. Banks Ram-Air system: the Banks 42138. A 4-inch aftermarket tube: a 4-inch inlet filter such as Wehrli's dry element. Then decide oiled or dry. Oiled cotton can be cleaned and re-oiled; dry elements are rinsed and need no oil. For any Sierra that works off pavement, add a pre-filter wrap sized to the element. Cold air intakes are the named upgrade on this platform with a cited 25-35 percent airflow gain, but that is the kit as a whole; a filter swap alone on a stock box is maintenance, not a modification.

What is in the collection

From S&B: the KF-1008 replacement filter for 2001-2005 Duramax, the KF-1035 that also fits 1994-2007 5.9L Cummins applications, and the WF-1023 filter wrap for S&B's 2001-2010 Duramax elements. From Banks Power: the 42138 filter element for the 6.6L Duramax and the 42643 pre-filter wrap built for it. From Wehrli Custom Fabrication: the WCF100717 4-inch inlet dry filter, a universal element that cross-lists to 2001-2024 Duramax, 2003-2018 Cummins and 2003-2007 6.0L Power Stroke. From PPE: the 115000105 element air filter for 2001-2005 Duramax. From Mahle: the LX2562 air filter for 2001-2005 Duramax.

Fitment notes for the Sierra

Trim does not matter here. Work Truck, SLE and SLT Sierras, 2500HD or 3500, single or dual rear wheel, all take the same element for a given intake. What matters is the intake brand and the tube diameter, and the product page for each filter states which system it serves. A wrap must match the element it covers. Broad cross-listings to Cummins and Power Stroke are a sign of a universal element, not a wrong part.

Frequently asked questions

My Sierra spools slow and runs hot towing. Could it be the filter?

It is the first thing to check. A restricted element produces the same lazy spool and high EGT that owners attribute to a sticking turbo, and BD Diesel puts filter and intake restriction ahead of any turbo work in its diagnostic order. Pull the element, hold it to the light, and replace it if it is loaded. Then check for boost leaks.

Which filter goes with the Banks pre-filter wrap?

The 42643 wrap is listed for the Banks 42138 air filter element used in Banks Ram-Air cold-air intake systems on 2001-2016 Duramax trucks. It is not a stock-box part. If you run an S&B kit, the matching wrap is the WF-1023.

Do I need a Duramax-specific filter, or will a universal 4-inch element work?

If you run a 4-inch aftermarket intake tube, a universal 4-inch inlet element such as the Wehrli WCF100717 fits by inlet size, which is why it is listed across Duramax, Cummins and Power Stroke years. For the factory airbox you need the 2001-2005 Duramax drop-in. Check the product page for the inlet size and system before ordering.

Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.