What This Filter Is and Where It Lives
91559 is the cabin air filter for Freightliner Cascadias built from 2004 up through the 2024 model year - that's a long production run, which is why one part number covers so many trucks. It filters the air coming into the cab through the HVAC system, catching road dust, pollen, diesel exhaust particulate, the usual stuff that clogs up a filter and starts making your defroster and blower motor work overtime.
On most Cascadias you'll find it behind a panel under the dash or behind the glovebox, depending on the cab configuration. Some trucks run two filters instead of one, so pull the old part and look for a second slot before you order just one and call it done.
This is a straightforward serviceable item - no wiring, no electronics, just a pleated filter media in a housing. Recommended service interval is usually somewhere around 12 months or 12,000 miles, but if you're running in dusty conditions or gravel yards, check it more often.
Why All These Numbers Cross to the Same Filter
Freightliner doesn't manufacture their own filters - they buy from the same filtration suppliers everybody else does, then stamp their own part number on the box. That's why Fleetguard's AF26235 and Donaldson's P609422 are the exact same filter, just packaged under different labels. Alliance parts, being Daimler's own aftermarket line, use N10G 91559 and N83 328385 for the identical piece.
Cabin air filters are simple enough that there's not a lot of variation to worry about compared to something with seals or splines. The main thing to check is the physical dimensions of the housing and whether your truck takes one filter or two - some Cascadia configurations changed over the model years, so a filter that fit a 2006 truck might not be the same size as a 2020.
Surest way to confirm is pull your old filter out and match it up dimension for dimension, or run your truck's VIN. If the old part has a number stamped on the frame, that'll cross-reference straight across, and any of the numbers in our chart above should get you the same filter.
Ordering From PartStop
We're out of Tacoma and keep this filter in stock because it's a high-turnover item - Cascadias are everywhere and this thing wears out. Local shops can usually get same-day pickup or delivery, and we ship nationwide if you're not in the Pacific Northwest.
At $21.53 this isn't a part where you need to overthink it, but we still tell everybody the same thing: confirm the fit against your VIN or the old filter before you order, especially if your truck might be running dual filters. Comes with our standard 6+ month warranty, and if something's off, call the counter and we'll sort it out.
91559 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to 91559. Use them to identify the part — then confirm the exact fit by VIN or the number stamped on your old unit before you order. An interchange is a starting point, not a fitment guarantee.
| Brand / Line | Cross-Reference Numbers |
|---|---|
| Fleetguard | AF26235 |
| Donaldson | P609422 |
| Alliance | ABPN10G91559, N10G 91559, N83 328385 |
| Cross-Reference | 10G-91559, BOA91559, VCCT1 |
Frequently asked questions
Does 91559 fit my 2015 Cascadia?
Likely yes - this filter covers the 2004-2024 Cascadia range - but confirm by checking your VIN or pulling the old filter and matching the number stamped on it, since some trucks in that range run dual filters instead of one.
Is this the same as the Fleetguard AF26235?
Yes, AF26235 is Fleetguard's number for the same filter - Freightliner sources these from the same suppliers as the aftermarket brands, so the numbers cross straight across.
How do I know if I need one filter or two?
Pull the panel where your old filter sits and look for a second slot next to it - some Cascadia cab configs came with dual filter housings. If you're not sure, snap a photo of your setup and we can help confirm before you order.
Not sure it fits? We check before you pay.
Run your VIN and we’ll match parts to your exact truck, or call the counter — a person who knows trucks verifies fitment by OEM number before the order ships. No wrong-box returns.
More cross-reference guides
Need the part, not just the reading?
Every part below is a Premium Quality aftermarket Direct Replacement with published OEM cross-reference numbers, a 6+ month warranty and same-business-day shipping from Tacoma, WA. Not sure it fits? Run your VIN — or call and a person who knows trucks will verify fitment before you pay.