The Lemon Index
The 6.6 L V8 turbo diesel in the Chevrolet Silverado 2500HD/3500HD and GMC Sierra 2500HD/3500HD, model years 2011–2016. Owners filed 779 complaints about trucks with it (matched by VIN); 13% name the engine, #5 of the 12 diesel truck engine generations we track (1 = the most).
Known issues, checked against owner complaints
Problems owners of trucks with this engine name much more often than owners of other diesel truck generations (at least 1.5× the median, and 10+ complaints):
- The CP4.2 high-pressure fuel pump. 83 of 779 owner complaints (11%) mention the CP4 or the high-pressure fuel pump, against a median of 0.3% for the other diesel truck generations we track.
My vehicles High Pressure Fuel Pump failed causing the vehicle to shutoff while driving. In addition, due to the engine shutting down while driving, the power steering quit working causing me to not be able to steer the vehicle. Thank you
2016 owner · NHTSA complaint 11666095 - The DPF / DEF system. 33 of 779 owner complaints (4.2%) mention the DPF, DEF or regen system, against a median of 0.1% for the other diesel truck generations we track.
Vehicle is being remotely hacked and placed into regen Parts have been swapped and truck has been tampered with and continues to be tampered with
2011 owner · NHTSA complaint 11686769
What YouTube owners say Tone 0-100, higher = more praise than trouble.
Average owner tone 42/100 across 6 model years, from 161 videos about this engine and its cars.
Most-watched videos
- What it takes to be at 730hp on a Duramax LML? 252,735 views
- Should I Delete my Duramax Diesel LML? 209,591 views
- BEFORE vs AFTER LML Duramax Delete Kit 154,091 views
Counted from video titles and captions: praise words against trouble words, weighted by views. Videos only count when the title names this engine or a car that had only this engine in those years.
Owner complaints by model year
Counts of complaints filed so far. Older trucks have had longer to collect them, and popular years draw more because more were sold: no one reports sales by engine, so there's no per-truck rate. Compare the shares below instead.
What owners complain about
Share of this engine's complaints that name each area (one complaint can name several).
What owners write
| Complaints that | Count | Share | Median, other diesel truck engines |
|---|---|---|---|
| Say the engine stalled, shut off or lost power | 130 | 17% | 7.8% |
| Mention the CP4 or the high-pressure fuel pump | 83 | 11% | 0.3% |
| Mention the DPF, DEF or regen system | 33 | 4.2% | 0.1% |
| Mention an injector | 31 | 4.0% | 1.2% |
| Mention the turbo | 13 | 1.7% | 1.0% |
| Mention the EGR system | 6 | 0.8% | 0.3% |
| Mention coolant loss or overheating | 6 | 0.8% | 0.8% |
Counted from the owner's own words in each complaint (all of the truck, not only the engine). A share, not a failure rate.
When problems show up
Half of the owners who gave a mileage reported the problem between 20,030 and 96,000 miles; the middle report was at 48,815 miles (466 complaints with a mileage).
Recalls that name this engine 0
No NHTSA recall on these trucks names this engine.
NHTSA recalls on these trucks and years whose text names this engine (its size, or diesel / Cummins / Duramax / Power Stroke). The rest (brakes, air bags, wiring ...) are on each truck year's page.
Trucks with this engine
In owners' words
I was pulling in my driveway and lost all steering, the wheel wouldn't turn, truck was still running fine no issues but the steering was out. Within 2 minutes the truck was fully engulfed in flames. With the fire starting from the hydroboost/power steering area.
2015 Chevrolet Silverado 2500HD/3500HD and GMC Sierra 2500HD/3500HD owner · NHTSA complaint 11769523
Leak is causing black mold, creating an unsafe environment inside the vehicle where child is expected and required by law to be buckled right above a black mold infected carpet and behind headrest
2016 Chevrolet Silverado 2500HD/3500HD and GMC Sierra 2500HD/3500HD owner · NHTSA complaint 11761963
Odometer Fraud. The contact purchased a 2015 Chevrolet Silverado 2500 from an auction. It was later discovered that there was a mileage discrepancy. At the time of the purchase, the vehicle mileage was 73,672. At the time of the vehicle registration, it was discovered that the mileage was 239,567.
2015 Chevrolet Silverado 2500HD/3500HD and GMC Sierra 2500HD/3500HD owner · NHTSA complaint 11735089
Against the other diesel truck engine generations
| Engine | Years | Complaints | Name the engine | Name the fuel system | Stalled or lost power | Recalls naming it |
|---|---|---|---|---|---|---|
| 6.0 Power Stroke | 2003–07 | 1,708 | 34% | 16% | 31% | 2 |
| 6.4 Power Stroke | 2008–10 | 572 | 28% | 7% | 11% | 2 |
| Duramax L5P | 2017–26 | 1,229 | 16% | 10% | 14% | 2 |
| 7.3 Power Stroke | 1999–03 | 2,049 | 15% | 5% | 12% | 1 |
| Duramax LML | 2011–16 | 779 | 13% | 20% | 17% | 0 |
| 6.7 Cummins | 2007–26 | 7,667 | 11% | 8% | 6.4% | 9 |
| 6.7 Power Stroke | 2011–26 | 5,640 | 10% | 11% | 7.8% | 6 |
| Duramax LBZ | 2006–07 | 186 | 8% | 5% | 7.0% | 0 |
| Duramax LMM | 2007–10 | 385 | 8% | 6% | 5.2% | 0 |
| Duramax LB7 | 2001–04 | 592 | 7% | 17% | 5.4% | 1 |
| Duramax LLY | 2004–06 | 374 | 7% | 11% | 7.8% | 0 |
| 5.9 Cummins | 1999–07 | 3,245 | 4% | 7% | 5.0% | 0 |
Shares of each engine's own complaints, matched by VIN. They show what owners complain about, not how often trucks break. Every diesel truck engine compared
Quick answers
Is the Duramax LML reliable?
No one reports sales by engine, so there's no per-truck score. Of the 779 complaints owners filed about trucks with it, 13% name the engine, #5 of 12 diesel truck engine generations we track (1 = the most). 83 (11%) mention the CP4 or the high-pressure fuel pump, against 0.3% for its peers. 33 (4.2%) mention the DPF, DEF or regen system, against 0.1% for its peers.
What trucks have the Duramax LML?
In our data: the Chevrolet Silverado 2500HD/3500HD and GMC Sierra 2500HD/3500HD, model years 2011–2016, matched by the VIN in each owner complaint.
What are the most common Duramax LML problems?
In owner complaints to the government: fuel system, electrical, steering.
How many recalls name the Duramax LML?
0 NHTSA recalls on these trucks name it.
Source: NHTSA owner complaints (FLAT_CMPL + COMPLAINTS_RECEIVED_2025-2026), received through 20261109; engines: NHTSA vPIC VIN decoder; NHTSA recalls API. Engine names and years: GM (RPO codes).