Next Level Performance
September 5, 2026 • 11 min read
Our Verdict
For a 2006–2010 BMW M5 or M6 throwing a P0420 or P0430 catalyst code, a matched pair of MagnaFlow OEM Grade direct-fit converters (PN 49803 driver + 49804 passenger) is the smart fix — roughly half the price of factory BMW cats, with the highest catalyst loading to keep the check-engine light off.
The S85 V10 uses one converter per side, so plan on buying both. Choose OEM Grade to pass emissions and clear codes cleanly; step down to the HM Grade high-flow versions if you want the most exhaust flow and a lower price on a track or off-road car.
Shop Our Top Pick →The BMW M5 & M6 V10 catalytic converters on the 2006–2010 E60 and E63/E64 are one of the most common — and most expensive — failure points on the legendary S85 engine. When the factory ceramic cats age out, the car logs P0420/P0430 catalyst-efficiency codes, dulls the throttle, and can even push the V10 into reduced-power mode. At NLP Performance in Tampa, FL, the fix our customers reach for most is a direct-fit MagnaFlow converter — a bolt-in stainless unit that costs roughly half of a dealer cat and reliably keeps the light off. This review breaks down MagnaFlow's OEM Grade and HM high-flow options for the S85, exact fitment, pricing, and how to choose.
Why Do the S85 V10 Catalytic Converters Fail?
The S85 V10's catalytic converters fail because 15-plus years of 8,250-rpm heat cycles break down the ceramic catalyst substrate, which then clogs, cracks, or loses efficiency and trips a catalyst-efficiency fault. The 5.0L S85 — rated at 500 hp at 7,750 rpm and 383 lb-ft at 6,100 rpm — runs extremely hot and uses one primary catalytic converter per cylinder bank, so a failure on either side sets its own code.
The two codes owners see most are P0420 (Catalyst System Efficiency Below Threshold, Bank 1) and P0430 (Bank 2). Beyond the check-engine light, symptoms include a lazy top-end pull, a faint sulfur smell, occasional rough idle, and — on a partially collapsed substrate — measurable back-pressure that saps power. Because a new BMW converter assembly runs well over $2,000 per side at the dealer, most S85 owners replace failed cats with a quality aftermarket direct-fit unit instead.
One important note: cat codes on an S85 are not always the cat itself. A lean fuel trim, a failing pre- or post-cat oxygen sensor, or an exhaust leak can mimic P0420/P0430. Confirm with live O2 data before buying — but once a converter has physically broken down, a replacement is the only real fix.
MagnaFlow spun stainless body with mandrel-bent tubing for the S85 V10.
What Is a Direct-Fit Catalytic Converter?
A direct-fit catalytic converter is a replacement cat engineered to bolt into the factory location using the original flanges, hangers, and sensor bungs — no cutting, welding, or fabrication required. That is the key difference from a universal converter, which is a bare cat body you (or a shop) must weld into the exhaust. For the S85, MagnaFlow's direct-fit units reuse the OEM mounting points on the E60/E63/E64, so a competent DIYer can swap one side in an afternoon.
MagnaFlow builds these converters with a spun stainless-steel body, free-flowing mandrel-bent tubing, and corrosion-resistant construction, and backs them with a 5-year / 50,000-mile MagnaFlow limited warranty. Every S85 direct-fit unit here is Federal/EPA compliant for 49-state use — note that these specific part numbers are not CARB-legal for registration in California. Buyers in Tampa and the other 48 states are good to go.
MagnaFlow OEM Grade vs HM High-Flow: Which Do You Need?
Choose OEM Grade if your M5 or M6 is a street car that has to pass emissions and clear codes; choose HM (high-flow) Grade if you want maximum exhaust flow and a lower price on a track or off-road build. Both are direct-fit and both are Federal/EPA 49-state parts — the difference is catalyst density.
OEM Grade (PN 49803 driver, 49804 passenger) uses the highest catalyst loading MagnaFlow offers for this application, which is what keeps a sensitive S85 DME from re-flagging P0420/P0430 after the swap. It is the safest choice for a daily-driven V10. HM Grade (PN 50420 driver, 50421 passenger, plus the value-priced 24228) uses a higher-flow core: it frees up a touch more exhaust flow and costs about $90–$100 less per side, but on a very sensitive ECU it is more likely to eventually set a soft catalyst code. For most owners keeping the car street-legal and hassle-free, the OEM Grade pair is worth the small premium.
MagnaFlow OEM Grade converter (PN 49804) for the S85 V10 passenger bank.
| Converter | Grade | Side | Emissions | Price |
|---|---|---|---|---|
| MagnaFlow OEM Grade Direct-Fit Converter – Passenger Side (49804)Top Pick | OEM Grade | Passenger (right) | 49-state EPA | $1,162.00 |
| MagnaFlow OEM Grade Direct-Fit Converter – Driver Side (49803) | OEM Grade | Driver (left) | 49-state EPA | $1,156.00 |
| MagnaFlow HM Grade High-Flow Converter – Passenger Side (50421) | HM high-flow | Passenger (right) | 49-state EPA | $1,067.00 |
| MagnaFlow HM Grade High-Flow Converter – Driver Side (50420) | HM high-flow | Driver (left) | 49-state EPA | $1,061.00 |
| MagnaFlow HM Grade High-Flow Converter – M6 Driver Side (24228) | HM high-flow | Driver (left) | 49-state EPA | $782.00 |
MagnaFlow S85 V10 Converters: The Options in Detail
Remember that the S85 needs a converter on each bank, so a complete job is one driver-side plus one passenger-side unit. Here are the direct-fit options we stock for the 2006–2010 M5 and M6, from the top-recommended OEM Grade pair down to the value-priced high-flow unit.
The HM Grade high-flow converter uses a freer-flowing core than the OEM Grade unit.
Key Specifications — MagnaFlow OEM Grade (49803 / 49804)
Installation & Fitment on the E60 M5 and E63/E64 M6
Installing a MagnaFlow direct-fit converter on the S85 is a bolt-in job: unbolt the failed converter at its factory flanges, transfer or replace the gaskets, and torque the new unit into the OEM location. Because each part number is side-specific, order the driver (left) and passenger (right) converters that match the bank you are servicing — or both if you are refreshing the whole exhaust. Plan on new flange gaskets and anti-seize on the O2 sensor threads.
Fitment covers the 2006–2010 BMW M5 (E60 sedan) and M6 (E63 coupe / E64 convertible) with the 5.0L S85 V10. Expect two to three hours per side for a DIYer with the car safely on stands, or a straightforward job for any independent BMW shop. After the swap, clear the codes and let the readiness monitors re-run; the OEM Grade cats are designed to satisfy the DME's catalyst-efficiency test on a healthy engine.
Shopping the rest of the exhaust? Pair your converters with a matched system from our exhaust collection, and browse related S85 maintenance parts to knock out oxygen sensors while you are under the car.
Factory-matched flanges and sensor bungs make the S85 converter a true bolt-in.
What We Like
- + Roughly half the cost of factory BMW converters
- + True bolt-in fit — no cutting or welding
- + OEM Grade catalyst loading clears P0420/P0430 reliably
- + Stainless construction with a 5-year / 50,000-mile warranty
Things to Consider
- – Not CARB-legal — 49-state (non-California) use only
- – Sold per side, so a full job means buying two units
Frequently Asked Questions
How much does it cost to replace the catalytic converters on a BMW M5 or M6 V10?
Replacing the S85 V10 catalytic converters with MagnaFlow direct-fit units costs roughly $1,850 to $2,325 for a full pair at NLP Performance, depending on grade — about $1,061 to $1,162 per side. That is roughly half the price of factory BMW converters, which run well over $2,000 each at the dealer. HM high-flow units start at $782 per side for the most budget-focused build.
What causes the P0420 or P0430 code on an E60 M5?
P0420 (Bank 1) and P0430 (Bank 2) mean the catalyst on that bank has dropped below its efficiency threshold. On a high-mileage S85 that is usually a physically worn-out converter — the ceramic substrate breaks down after years of high-rpm heat. Rule out lean fuel trims, a failing oxygen sensor, or an exhaust leak first, but a collapsed cat requires replacement.
Are MagnaFlow direct-fit converters legal in my state?
These MagnaFlow S85 part numbers are Federal/EPA compliant for use in 49 states but are not CARB-approved, so they cannot be registered on a street car in California. For Tampa, FL and the rest of the country outside California, they are street-legal direct replacements.
Do I need to replace both catalytic converters at once?
Not necessarily — each converter and each code is bank-specific, so you can replace only the failed side. However, because both cats are the same age and heat-cycled equally, many S85 owners replace both at once to avoid a second job when the other side fails shortly after.
What is the difference between MagnaFlow OEM Grade and HM Grade converters?
OEM Grade (PN 49803/49804) uses the highest catalyst loading, which best keeps the check-engine light off on a street-driven M5 or M6. HM Grade (PN 50420/50421/24228) uses a higher-flow core that frees up slightly more exhaust flow at a lower price, but is more likely to set a soft code on a very sensitive DME over time.
Will new catalytic converters add horsepower to my S85?
Replacing a clogged, failing converter restores lost power and throttle response, so you will feel a difference over a bad cat. But going from a healthy OEM cat to a high-flow unit yields only marginal gains on the naturally aspirated S85 — the real value here is reliability, emissions compliance, and clearing catalyst codes, not big dyno numbers.
Keep Your V10 On the Road
Shop direct-fit MagnaFlow converters and thousands more performance parts for your BMW M5 and M6 at NLP Performance.
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