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Here is the thing almost every “best glow plugs” list leaves out: on a 2011-2016 LML Duramax, the glow plugs are frequently not the reason the truck cranks long on a cold morning. The engine has eight plugs, and the glow plug control module switches each one individually — which means the module also reports on each one individually. So the pattern of trouble codes is the real diagnostic, not the symptom. One or two codes (a P0671 here, a P0678 there) points at those specific plugs. Eight codes at once almost never means eight dead plugs. It means the thing feeding all eight has stopped feeding them: the control module itself, its ground, the 15-amp fuse in the underhood block, or one of the big mega-fuses upstream of it. Buying eight plugs to fix that is an afternoon of work and a set of parts that were already fine.
The second thing the lists leave out is that glow plug choice on this engine is close to a solved problem. GM’s own plug carries part number 12639701; ACDelco sells the same plug as the 9G; Bosch’s 0250203011 is the other genuinely OEM-grade option. All three cover the whole 2006-2016 LBZ/LMM/LML family. There is no “performance” plug that makes an LML start meaningfully faster, because the limiting factor is the glow cycle the ECM commands, not the element. What you are actually shopping for is a plug that heats to spec and, far more importantly, one that comes out again in five years without snapping off in an aluminium cylinder head.
That last risk is why this list is not eight identical plugs and two filler items. It covers the plugs worth buying, the control module that fails alongside them, and the small handful of tools and consumables that decide whether the job takes two hours or ends with the head off the truck. Read the codes first, buy once, and torque them properly.
| # | Product | Price | Where to buy |
|---|---|---|---|
| 1 | ACDelco Professional 9G Glow Plug | $18-$30 each | Amazon · eBay |
| 2 | Bosch 0250203011 Glow Plug | $16-$28 each, $130-$210 a set | Amazon |
| 3 | GM Genuine Parts 12639701 Glow Plug Set | $180-$280 a set | Amazon · eBay |
| 4 | Glow Plug Control Module (GPCM) for 2011-2016 LML | $90-$220 | Amazon |
| 5 | Glow Plug Harness and Pigtail Connector Set | $20-$50 a set | Amazon |
| 6 | 10 mm Deep Glow Plug Socket with Swivel | $15-$45 | Amazon · eBay |
| 7 | Penetrating Oil for Seized Glow Plugs | $8-$20 | Amazon |
| 8 | Nickel Anti-Seize Compound | $10-$22 | Amazon · eBay |
| 9 | 3/8 in Click-Type Torque Wrench, 5-80 ft-lb | $40-$140 | Amazon · eBay |
| 10 | OBD-II Scan Tool with Enhanced GM Diesel Codes | $60-$300 | Amazon |
The picks, in detail
ACDelco Professional 9G Glow Plug
The default answer, and the one most Duramax shops fit. It is the same plug GM supplies under 12639701, boxed under the ACDelco Professional line, and it fits every 6.6 from the LBZ through the LML. Sold individually, so a full job is eight of them. There is no meaningful heating-performance argument between this and Bosch — pick on price and on which one you can get in a set of eight from one seller, because mixing suppliers is how people end up with seven plugs and a week of downtime.
- OEM-equivalent to GM 12639701
- Covers 2006-2016 LBZ, LMM, LGH and LML
- Sold singly — order eight for a full set
- Standard 10 mm hex body
- The part GM specifies, with no cross-reference guesswork
- Widely stocked, so a set of eight is easy to source together
- Consistent heat-up with the factory glow strategy
- Priced per plug, so the full set adds up
- No advantage over Bosch beyond availability
Bosch 0250203011 Glow Plug
Bosch builds an enormous share of the world’s diesel glow plugs, including plugs for engines badged by other names, and the 0250203011 is its Duramax-fitment part. Functionally you are choosing between this and the ACDelco; both are genuinely OEM-grade rather than an equivalent. Where Bosch often wins is the packaging — it is easier to find listed as a set of eight in one box, which removes the single most common ordering mistake on this job. Check the part number on the listing rather than the marketing copy, because Bosch lists more than one Duramax plug across the generations.
- Bosch part 0250203011, OEM-grade construction
- Fits 2006-2016 6.6L LBZ/LMM/LML
- Commonly available as a boxed set of eight
- Sheathed element, conventional (non-ceramic) design
- Set-of-eight packaging avoids mismatched orders
- Identical service life expectations to the ACDelco
- Easy to verify by part number
- Multiple Bosch Duramax part numbers exist — the wrong one fits the wrong generation
- Counterfeit Bosch plugs circulate; buy from a diesel specialist or a known seller
GM Genuine Parts 12639701 Glow Plug Set
The dealer part, bought as a set. It is the most expensive way to do this and the least likely to go wrong: one part number, eight plugs, no cross-referencing. If your truck is still under any kind of powertrain coverage, or you simply do not want to spend an evening confirming that an aftermarket listing really covers the LML and not just the LB7, this is what that certainty costs. Worth noting that the set is the same plug as the ACDelco 9G — you are paying for the GM box and the guaranteed count, not a different part.
- GM part number 12639701
- Eight plugs in one order
- Factory fitment for 2011-2016 LML
- Dealer-network parts warranty
- Zero fitment ambiguity
- Arrives as a complete set
- The reference part everything else is cross-referenced against
- Noticeably dearer than the identical ACDelco-boxed plug
- Dealer stock can be slow in some regions
Glow Plug Control Module (GPCM) for 2011-2016 LML
The part that should be on your shortlist before the plugs are, if you are seeing a wall of codes rather than one or two. The module switches each plug individually and reports each one individually, so when it loses its supply or its internal drivers fail, the scan tool shows the whole bank as faulty. Replacing it is a far smaller job than replacing plugs — it is mounted on the engine, not buried under the intake — and a rebuilt or new module costs less than a set of eight plugs. Diagnose before you buy either.
- Controls and monitors all eight plugs independently
- LML-specific connector and calibration
- New and remanufactured options available
- Accessible without removing intake plumbing
- Fixes the all-eight-codes pattern that plugs will not
- Cheaper and faster to fit than a full plug set
- Rules out the most commonly misdiagnosed part on the system
- Some listings cover LBZ/LMM only — LML calibration differs
- A failed module is often a symptom of a supply or ground fault that will kill the new one too
Glow Plug Harness and Pigtail Connector Set
The connector that clips onto each plug lives in the hottest, dirtiest part of the engine bay and it gets brittle. A green, crumbling pigtail will read as a dead plug on a scan tool and will keep reading that way after you have fitted a brand-new plug underneath it. Pigtails cost a few dollars each, they are the one part of the circuit you can inspect visually without a meter, and replacing them while the plugs are out costs no extra labour at all. Buy a set when you buy plugs; if they look fine, you have spent very little.
- Replaces heat-damaged individual plug connectors
- Sold in sets covering all eight cylinders
- Crimp or solder-and-seal terminations
- Same fitment across LBZ through LML
- Cures phantom plug codes that new plugs do not
- Trivial cost alongside the rest of the job
- Zero extra labour if fitted during a plug change
- Requires a decent crimp or solder joint to last
- Quality varies sharply between cheap listings
10 mm Deep Glow Plug Socket with Swivel
Not optional. The plugs sit down a bore that runs at an angle, and a standard deep socket will either not reach or will load the plug sideways as you break it loose — which is exactly how a plug snaps. A proper glow plug socket has a thin wall, a magnet or rubber insert to hold the plug on the way out, and a swivel that lets the extension take the angle out. It costs less than one plug. The whole risk in this job is sideways load on a seized plug in an aluminium head, and this is the tool that removes it.
- Thin-wall 10 mm design for the plug bore
- Universal swivel joint to clear the angle
- Magnetic or rubber plug retention
- 3/8 in drive with long extension
- Keeps load axial, which is the whole game here
- Retains the plug so it does not drop into the bay
- Cheap insurance against a head-off repair
- Cheap swivels develop play and reintroduce side load
- Some kits omit the long extension you actually need
Penetrating Oil for Seized Glow Plugs
A plug that has been in a hot aluminium head for five winters is carbon-locked, not just tight. The right sequence is penetrant, a partial turn, more penetrant, and a heat cycle or two — days, not minutes, if the truck can sit. Reach for a penetrant with a genuine capillary-creep formulation rather than a general-purpose spray lubricant; the two are sold next to each other and they are not the same product. It is a five-dollar bottle standing between an easy job and a cylinder head coming off a truck.
- Low-viscosity capillary creep formula
- Straw applicator for the plug bore
- Works across repeated heat cycles
- Safe on aluminium threads
- Cheapest possible mitigation for the job’s one real risk
- Can be applied days ahead with no downtime
- Useful on exhaust and turbo fasteners on the same truck
- Needs patience and repeat applications — not a one-spray fix
- General-purpose lubricants sold alongside it do not work the same way
Nickel Anti-Seize Compound
Use it on the threads of the new plugs, sparingly, and keep it off the element. Nickel-based compound is the one to buy for this: copper-based products are not recommended around some sensor circuits, and a plug is an electrical component earthed through its own threads. The important discipline is quantity — a thin film on the thread, never on the tip and never so much that it squeezes into the combustion chamber. And remember anti-seize changes the friction, so you torque to the figure in the manual, not to feel.
- Nickel-based, high-temperature
- Brush-in-cap applicator
- Rated well beyond cylinder head temperatures
- A single small tub covers many jobs
- Makes the next plug change straightforward
- Protects aluminium threads from galling
- One tub lasts years
- Over-application is genuinely harmful on the tip
- Alters torque readings — you must use a wrench, not feel
3/8 in Click-Type Torque Wrench, 5-80 ft-lb
Glow plugs go into aluminium at a modest torque figure, and both directions of error are expensive: under-torqued plugs work loose and blow out, over-torqued plugs strip the thread or shear at the shoulder. This is not a place to guess, particularly with anti-seize on the threads changing how tight tight feels. A mid-range click wrench covering roughly 5 to 80 ft-lb spans plugs, valve covers and most of the fasteners you will disturb getting to them. Check the actual figure for your model year in a service manual rather than taking a forum number.
- 3/8 in drive, roughly 5-80 ft-lb span
- Audible click with a positive detent
- Reversible ratchet head
- Calibration certificate on better models
- Covers the plugs and everything else you remove to reach them
- Removes the guesswork anti-seize introduces
- Holds calibration for years with light use
- Cheap wrenches drift out of calibration quickly
- Must be wound back to its lowest setting for storage
OBD-II Scan Tool with Enhanced GM Diesel Codes
The cheapest code reader will tell you there is a problem; it will not tell you which cylinder. You need a tool that reads GM enhanced powertrain codes so you can see the individual P0671 through P0678 entries and, ideally, live glow plug data. That distinction is the entire point of this article: the pattern of codes decides whether you buy one plug, eight plugs, or a control module. Spending a little more here to see per-cylinder detail routinely saves the price of a set of plugs you did not need.
- Reads enhanced GM powertrain codes, not just generic
- Per-cylinder glow plug fault reporting
- Live data streaming
- Bluetooth dongle or handheld formats
- Turns a vague no-start into a specific part number
- Pays for itself on the first correct diagnosis
- Useful across the rest of the truck
- Generic budget readers will not show the per-cylinder codes
- Some subscription apps charge extra for the enhanced code set
Buying tips
- Read the codes before you order anything. One or two of P0671-P0678 means those specific cylinders. All eight at once points upstream — the control module, its ground, the 15-amp fuse in the underhood block, or the mega-fuses feeding it. Fixing a module fault by fitting eight plugs is the most common and most expensive mistake on this engine, and it is entirely avoidable with a scan tool that shows per-cylinder detail.
- Do not fight a stuck plug on a cold engine, and do not fight it in one session. Penetrant, a small turn, penetrant again, a heat cycle, repeat. Working a seized plug loose over three days costs nothing; snapping one off costs a cylinder head removal, because there is no room to extract the broken element from above. If the truck is your daily driver, start the penetrant a week before you plan the job.
- Buy all eight at once, from one seller. They have the same age and the same duty cycle, so one plug failing is a signal about the rest of the set. Half a set means the labour gets paid twice. It also avoids the specific annoyance of discovering a supplier has seven in stock after the intake is already off the truck.
- Check the part number, not the fitment blurb. Bosch and ACDelco both list several Duramax glow plugs across the LB7, LLY, LBZ, LMM and LML generations, and marketplace listings copy fitment tables carelessly. The ones that cover 2011-2016 LML are GM 12639701, ACDelco 9G and Bosch 0250203011. Match the number in the listing photo, not the title.
- Replace the pigtails while you are in there. The individual connectors bake and go brittle, and a bad one produces exactly the same code as a dead plug. They cost a few dollars per cylinder and take no extra time once the plugs are out. Skipping them is how people finish the job and still have a code on the dash.
- Torque to the manual figure, with a wrench. Aluminium threads punish both under- and over-tightening, and anti-seize on the threads makes the plug feel tight well before it is correctly loaded. Look the figure up for your model year rather than taking a number from a forum post about a different Duramax generation.
- Long crank plus white smoke on a cold start is the classic plug symptom. A healthy LML fires almost immediately once the wait-to-start light clears. Holding the key for several seconds below about 40 °F, with white smoke, means fuel is going into cylinders that are not hot enough to light it. A wait-to-start light that stays on or flashes points more towards the module.
- If a new module fails quickly, stop replacing modules. A control module that dies twice is usually being killed by something else — a chafed harness shorting a plug circuit, a corroded ground, or a plug that has failed short rather than open. Find the fault with a meter before fitting a third module, or you will simply keep buying the same part.
As an Amazon Associate and eBay Partner, toptenpick.com earns from qualifying purchases. Prices and availability are subject to change.