That's the LML's CP4.2 high-pressure pump letting go, and it has sent metal through your entire fuel system. We replace the whole system — pump, injectors, rails, lines — at your home.
The 2011–2016 Duramax LML uses the Bosch CP4.2 high-pressure fuel pump — a design that runs on a knife's edge of lubrication. Diesel fuel itself lubricates the pump's roller followers, and North American diesel is drier than the European fuel the pump was designed around. When the lubrication film breaks down, a roller skews on its cam, and the two surfaces start grinding each other into metal dust.
Here's what makes the CP4.2 failure catastrophic rather than just expensive: that metal dust doesn't stay in the pump. The pump pushes it downstream at tens of thousands of PSI — through the rails, through the lines, and into all eight injectors, whose internal tolerances are measured in microns. By the time the truck won't start, the debris is everywhere the fuel goes.
This is why there's no such thing as 'just replacing the pump.' A new pump fed by contaminated rails and returning fuel through contaminated injectors fails again, fast — and that second failure isn't covered by anyone. The only honest repair is the complete system: pump, all eight injectors, rails, lines, a full tank-to-engine decontamination, and new filters. It's a huge job, which is exactly why getting it done right the first time matters.
If your GM is doing any of these, this is the likely cause:
If your truck still runs but you've found metal in the filter, stop driving it — every kilometre pushes more debris deeper into the injectors and rails. Caught at the first metal, sometimes the contamination is containable; driven until the no-start, it's always the full system. And once it's dead, it's dead: there's no limp-home with a spalled CP4.2. The decision window on this failure is measured in tanks of fuel, not months.
Yes — it's two days of methodical work, but everything involved (tank, pump, rails, injectors, lines) comes apart with the truck on jack stands in a driveway. Since the truck usually can't drive anyway, mobile repair skips the tow on top of everything else.
Because the honest repair really is the entire fuel system — eight injectors alone are thousands in parts — plus dozens of book hours, all at dealer rates. The parts list is non-negotiable; the labour rate isn't. We quote one flat price for the complete job, every part listed, before we begin.
Anyone who offers that is selling you a second failure. Microscopic metal is already through the rails and injectors, and injectors pass debris back into the system. A pump-only fix on a CP4.2 failure typically dies within weeks. We won't do half the job — it wastes your money.
Clean fuel and religious filter changes are the biggest factors, since the CP4.2 lives and dies by fuel lubricity. If you're proactive on a healthy LML, ask us about preventive options when we're there — addressing it before failure is a fraction of the cost of after.
Send it over for a free second opinion. I'll tell you straight what the job actually involves — and if their quote is fair, I'll tell you that too.
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