Classic dead glow plugs — and on a Duramax they seize and snap in the aluminum heads if they're forced. We replace all eight plus the controller, carefully, at your home.
Glow plugs are what make a diesel start in an Ontario winter — small heating elements that pre-warm each cylinder so cold, dense air can still light the fuel. On the Duramax they live threaded into aluminum cylinder heads, and over years of heat cycles two things happen: the heating elements burn out one by one, and the steel plug bodies corrode and seize into the aluminum threads.
The controller fails too — it's the module that decides how long the plugs heat and feeds them current, and when it goes, even good plugs don't fire. That's where the P0670 through P0678 codes come from: P0670 is the control circuit, and the individual cylinder codes tell you which plugs have died. A truck might start fine at 5°C and become a 30-second white-smoke ordeal at -15°C.
Here's why this job is rated heavy despite sounding simple: a seized glow plug forced out of an aluminum head snaps off, and now a routine service becomes head removal or delicate extraction work. The plugs need penetrating treatment, heat-cycle technique, and patience — exactly the discipline a rushed shop bay doesn't have. Done carefully, with the controller replaced at the same time, the truck fires like new in any temperature.
If your GM is doing any of these, this is the likely cause:
Every dead glow plug makes the remaining ones and your starter work harder, and Ontario cold snaps don't negotiate — the morning it won't start will be the -20°C morning you need it most. There's a mechanical cost too: prolonged cold cranking washes oil off cylinder walls and floods raw fuel into the exhaust. And the longer seized plugs stay in the heads, the more corroded and snap-prone they get. This job only gets riskier with age.
Yes — glow plugs and the controller are engine-in-truck work, done at your driveway in most of a day. The value of mobile here is the unhurried, careful extraction these seized plugs demand. We bring everything.
The parts are modest — the labour risk is what's priced in. On a Duramax, every plug is a potential snap-off in an aluminum head, and the careful technique to prevent that takes hours. We quote one flat price for all eight plus the controller before starting, and we tell you upfront how we handle the rare breakage case rather than burying it in fine print.
We plan so it doesn't — penetrant soak, heat cycles, staged back-and-forth torque. If one is seized beyond saving, we stop and discuss extraction options with you before any drastic step. What we never do is force it and hand you a surprise.
Because all eight plugs are the same age with the same hours, and the labour to get to them is the job's real cost. Replace two now and you'll pay that labour again next winter for the next two. One visit, the whole system — plugs and controller — and cold starts are solved for years.
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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