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A Duramax CP4 pump failure sends metal through the entire fuel system, which is why it's a genuinely big job — not a dealer gouge. Dealers quote north of $10,000 for the full fuel-system replacement on a 2500HD. Cars With Fares explains exactly what failed and does the job right in your own driveway across the GTA, flat-quoted first. Call or text 647-450-0406.
If a dealer just handed you a quote north of $10,000 for a "fuel system contamination" job on your 2500HD, I know exactly what you're staring at — and I know your stomach dropped. That number is real, and on a CP4 failure it's not even a gouge; it's genuinely a big job. But the dealer write-up almost never explains why it costs that, what's actually broken, or what your real options are. So before you sign anything, let me walk you through what happened to your truck, what the honest fix is, and what I charge to do the whole thing right in your own driveway.
The short version: your Bosch CP4.2 high-pressure injection pump ate itself and sent metal through your entire fuel system. That's the failure on the 2011–2016 LML 6.6 Duramax — the Silverado and Sierra 2500HD/3500HD. It's not a "replace the pump and go" situation, and any shop telling you it is will have you back in a month. Here's the whole picture.
The LML uses a Bosch CP4.2 high-pressure pump to push fuel up to common-rail pressures. The problem is built into the design. Bosch engineered the CP4 around European diesel, which is more lubricating than the ultra-low-sulfur diesel (ULSD) we run here. Our fuel is drier. So the pump's internal roller lifter and camshaft — the parts that don't get enough lubrication — wear, gall, and eventually the roller can cock sideways and dig into the cam.
The second it starts grinding metal off itself, you've got a much bigger problem than a dead pump. The CP4 sits on the high-pressure side, so it shoots those steel shavings downstream into the rails and injectors at thousands of PSI. And the LML runs a closed-loop fuel system — return fuel cycles back through — so that metal keeps circulating through everything, and there's no filter on the high side to catch it. By the time the pump finally lets go, the contamination is already everywhere.
That's the part the sticker shock hides. You're not paying for a pump. You're paying to decontaminate an entire fuel system that's been sandblasted from the inside.
Almost every LML CP4 call I get sounds the same on the phone, and it usually shows up one of two ways.
The slow one: the truck starts getting harder to fire on cold mornings, you lose a bit of power, maybe a check engine light for low rail pressure. Owner thinks it's a glow plug or a filter. It's the pump starting to go.
The bad one — and this is most of them — is sudden and total. Truck's running fine, then it drops on its face, throws a code, and either limps or dies on the spot. Try to restart and it just cranks: long crank, no fire, sometimes a strong diesel smell. Here's the tell that confirms it for me before I even pull a pump: I cut open the fuel filter and there's a grey, glittery sludge or fine metal in it. That metal is the inside of your CP4. Once I see that, I'm not guessing anymore.
Had a guy out near the 410 and Steeles in Brampton, '13 Sierra 2500 he used for his landscaping crew — died pulling a loaded trailer up the ramp onto the 410. He thought he'd run it dry. Cracked the filter open and it was full of metal. That's a CP4, every time.
Here's where I'll be straight with you, because this is where shops cut corners and customers get burned. A flush is not a fix. Replacing only the pump is not a fix. If metal got pushed through the system — and on a failed CP4 it did — you replace the contaminated parts, period. The complete, correct job on an LML is:
I won't do this job halfway. If someone tells you they'll "just swap the pump and flush it to save you money," walk away — because when the new pump grenades on leftover metal in three weeks, you're paying for the whole thing twice. Do it once, do it right.
Let's talk real numbers, because that's why you're here. The dealer on a complete LML CP4 contamination job is generally $10,000 to $14,000. That's not them ripping you off on the CP4 specifically — it's a pump, eight injectors, rails, lines, the regulator, and the labour to clean a whole system. It's an expensive repair anywhere.
I do the same complete job — the real one, not the band-aid — at your place for a flat quote that usually lands around $8,500, depending on which parts have already let go and what we decide on the pump (OEM CP4 vs. an updated/CP3-style setup). You get the number in full before I touch a wrench. No "while we were in there" surprises, no shop time ticking. That you end up paying less than the dealer is real — but it's not the pitch. The pitch is you get the honest, complete repair from one guy who tells you exactly what's getting replaced and why, and your work truck doesn't disappear into a service bay for two weeks during your busy season.
Tell my AI mechanic what your Duramax is doing — hard start, power loss, what the fuel filter looks like — and it'll give you an honest read on whether you're looking at a CP4 failure or something cheaper. Then I confirm it at your truck.
Ask the AI mechanic →Don't keep driving it
This is one of the few jobs where I tell people flatly: stop driving it. Not to scare you — because the physics are against you. The moment the CP4 starts shedding, every kilometre and every crank pushes more metal deeper into the injectors and rails. A truck caught early, with the pump just starting to go, is a smaller bill than one that got driven another 300 km on a failing pump because the owner "wanted to see if it'd clear up." It won't clear up. It gets more expensive by the day.
So if you've got metal in the filter, a sudden power loss, or it cranks and won't fire — don't keep cranking it and don't keep driving it. Get it shut down. Towing your truck a few kilometres is far cheaper than running steel through eight more injectors. That's the one piece of this I'd push you on.
If it's still just the early, slow symptoms — a little harder to start, slightly down on power, no metal in the filter yet — you've got a little more room, but not much. Get it diagnosed this week, not next month. The window where this stays "small" is short.
A CP4 job is exactly the kind of repair where who's doing it matters more than where. It's a big-ticket diesel job with a lot of room for a shop to cut a corner you'll never see — reuse an injector, skip a rail, flush instead of replace — and you don't find out until it fails again. When I do it in your driveway, you can literally watch what comes off your truck. I'll show you the metal in your old filter. I'll show you which parts are going back on. There's no service-desk middleman marking up parts and no mystery on the invoice.
And practically — this is usually somebody's work truck. A contractor's 3500, a landscaper's 2500, a guy who tows for a living. Dropping it at a dealer means it's gone for a week or two during the season you actually need it. I come to you, off the 401 corridor through Mississauga, Brampton, Vaughan, out to Milton and Oakville, and the truck stays where you can keep an eye on it. We come to you — that's the whole point.
Our winters make this worse in two ways. Cold-soaked diesel is harder on an already-marginal pump, so a borderline CP4 often picks the first hard freeze to finally let go — I get a wave of these calls in January. And the salt: every fuel and high-pressure line under a 10-year-old Ontario truck is rust-seized at the fittings. That salt-belt corrosion is real labour on this job, because half the fight is breaking loose lines that haven't moved since the truck left the lot. It's why a clean Alberta truck and a rusty Mississauga one aren't the same job — and I price yours for what's actually under it, not a textbook number.
If your truck's already down: don't crank it again. Call or text me at 647-450-0406, tell me the year and what it's doing, and I'll tell you straight whether it sounds like a CP4 or something cheaper before you spend a dime. If it is the pump, I'll come to your truck, confirm it, and give you the full flat quote before any work starts. Mobile diesel repair across Mississauga, Toronto, Brampton, Vaughan, Milton, Oakville & the GTA.
Done properly it's a full fuel-system job, not just a pump. The dealer on a 2011–2016 LML usually quotes between $10,000 and $14,000 because they replace the CP4 pump, all eight injectors, both fuel rails, the high-pressure lines and the fuel pressure regulator, then flush and refill the rest of the system. I do the same complete job at your place for a flat quote that typically lands around $8,500 depending on which parts have already let go — quoted in full before I touch it.
When the CP4 pump fails it grinds metal off its own roller and cam and pushes those shavings downstream at very high pressure. The LML runs a closed-loop fuel system, so that metal circulates through the injectors, the rails and the lines without being filtered out. By the time the pump is dead, the whole system is contaminated. Replacing only the pump just feeds the new one metal from the old parts and it fails again — which is why the complete job is the only fix that holds.
No. Once it starts shedding metal, every minute of run time pushes more contamination deeper into the injectors and rails, which makes a big repair bigger. If you've got hard starting, sudden power loss, metal in the fuel filter, or it cranks and won't fire, stop driving it and don't keep cranking. Have it looked at before you turn the key again — towing it is cheaper than running metal through more parts.
The Bosch CP4.2 that self-destructs is on the 2011–2016 LML 6.6 Duramax in the Silverado and Sierra 2500HD and 3500HD — that's the one. The 2001–2010 trucks (LB7, LLY, LBZ, LMM) used the earlier CP3 pump, which is built far tougher and doesn't have this failure. And the 2017+ L5P trucks switched to the Denso HP4 pump, which GM put in specifically to fix this — so a true CP4 contamination grenade is an LML thing, 2011 to 2016.
I do it where the truck is — your driveway, your yard, or the job site. We come to you. A CP4 contamination job is involved but it's mechanical work I can do on location with the right tools and clean fuel handling. I diagnose it, confirm the contamination, quote the full job flat, and do it at your place across Mississauga and the GTA so your truck isn't sitting at a dealer for two weeks.
I'll tell you straight whether it's the CP4 — then fix it right at your truck, quoted flat before any work. Mobile diesel specialist across the GTA.
Call 647-450-0406