2011–2016 CHEVY SILVERADO / GMC SIERRA HD · 6.6L DURAMAX LML
LML Duramax repair in Tucson: weak points & fixes.
The LML is strong and quiet with lots of torque, but its CP4 fuel pump is a known weak spot, and it added DEF and more emissions sensors. Here’s what we see on these trucks and how we fix it at your location.
- 397 hp765 lb-ft stock
- Bosch CP4.2DPF + DEF/SCR
- Allison 10006-speed automatic
- We come to youTucson & nearby
Jump to a system
KNOW YOUR TRUCK
Early or late LML? It changes the parts.
The LML ran six years with two body styles. Intakes and some emissions parts change by year.
GMT900 body
- 397 hp / 765 lb-ft
- First Duramax with DEF
- 2011 trucks saw the most DEF and NOx sensor problems
- Banks intake: one part for 2011–2012, another for 2013–2014
K2 body
- Same 397 hp / 765 lb-ft
- New body and interior
- Separate Banks intake for 2015–2016
- VIN 8th digit “8” on all LMLs
POWER THROUGH THE YEARS
Where the LML Duramax fits in Duramax history.
Peak factory pickup ratings by generation, horsepower and torque. Yours is highlighted. Tap any bar to see that generation.
- Horsepower
- Torque (lb-ft)
WEAK POINTS, SYSTEM BY SYSTEM
What fails on the LML Duramax, and how we fix it.
Tap a system to see what fails, what you’ll notice and how we fix it. Common = we see it often. Towing / tuned = shows up with heavy loads or added power. High miles = age and wear items.
Fuel system
CP4.2 pump failureCommon
You’ll notice: sudden no-start or stall, low rail pressure codes, metal in the fuel filter.
Why: The CP4 can wear and send metal through the whole fuel system, taking out injectors, rails and lines with it. Water or bad fuel makes it worse.
Our fix: We repair the fuel system, and we recommend a 50-state legal S&S CP3 conversion to prevent it.
Water in the fuelCommon
You’ll notice: a water-in-fuel light, rough running.
Why: Water is hard on the CP4 and the injectors.
Our fix: We drain and clean the system and add a FASS lift pump with water separation.
Injector wearHigh miles
You’ll notice: smoke, a miss, rough idle.
Why: Piezo injectors wear with miles or get damaged by a pump failure.
Our fix: We test the injectors and replace them with quality units.
DEF, DPF & EGR
DEF heater, pump and sensorsCommon
You’ll notice: a “Service DEF” message, a countdown to reduced speed, poor DEF quality warnings.
Why: The DEF heater, pump and quality sensor are common failures, especially on 2011 trucks.
Our fix: We diagnose the system and replace the failed part, keeping it legal.
NOx sensorsCommon
You’ll notice: check engine light, derate, failed regens.
Why: NOx sensors fail with heat and age.
Our fix: We test them and replace the failed sensor.
DPF and EGRHigh miles
You’ll notice: frequent regens, low power, coolant loss, EGR codes.
Why: Soot loads the DPF and EGR parts, and the EGR cooler can leak.
Our fix: We clean or replace emissions parts the legal way.
Cooling & leaks
Water pump and coolant leaksHigh miles
You’ll notice: coolant drips, running hot.
Why: Pumps and hoses wear with age.
Our fix: We pressure-test and replace what’s leaking.
Allison 1000 automatic
Slipping or limp modeTowing / tuned
You’ll notice: flare between gears, harsh shifts, limp mode.
Why: Old fluid, heat and added power wear out the Allison’s clutches.
Our fix: We service it, diagnose the codes and rebuild with heavy-duty parts when needed.
Front end & steering
Loose steeringCommonHigh miles
You’ll notice: wandering, play in the wheel, uneven tire wear.
Why: The independent front end wears out idler arms, pitman arms, tie rods and ball joints on these heavy trucks.
Our fix: We rebuild the front end with heavy-duty parts and set the alignment.
RELIABILITY UPGRADES
Bulletproof it in the right order.
If you plan to keep your LML, these are the upgrades we recommend, in the order that protects it best.
- CP3 conversionA 50-state legal S&S kit replaces the CP4 before it fails.Call nowRequest a quote
- Lift pumpA FASS lift pump keeps water and air out of the fuel system.Call nowRequest a quote
- Fuel filter on timeFresh filters and drained water protect the pump and injectors.Call nowRequest a quote
- Transmission coolingA PPE deep pan adds fluid and cooling for the Allison.Call nowRequest a quote
- GaugesExhaust temp and transmission temp gauges protect the truck when towing.Call nowRequest a quote
MAINTENANCE SCHEDULE
LML Duramax service intervals.
These are GM’s factory intervals from the owner’s manual schedule. The factory “severe” column covers towing, dusty roads, short trips and long idling, which describes most working trucks in Southern Arizona. Our recommendation follows the severe schedule, with oil every 5,000 miles and fuel filters every 10,000.
| Service | Factory, normal use | Factory, severe use | Our recommendation |
|---|---|---|---|
| Engine oil & filter | 10,000 mi / 12 months or oil life monitor (maximum) | Sooner when towing or idling | Every 5,000 mi |
| Fuel filter & water separator | 22,500 mi / 2 years or dash message | Same | Every 10,000 mi |
| Engine air filter | 45,000 mi / 4 years or dash message | Check at every oil change | Check at every oil change |
| Coolant | 150,000 mi / 5 years first, then 50,000 mi | Same | 150,000 mi / 5 years first, then 50,000 mi |
| Allison external filter | 45,000 mi | Same | 45,000 mi |
| Allison full fluid & filter service | 97,500 mi | 45,000 mi | 45,000 mi |
| Transfer case fluid | 97,500 mi | 22,500 mi | 22,500 mi |
| Front & rear axle fluid | Not set by the factory | Not set by the factory | No factory interval; we inspect it at every service |
Always go by your owner’s manual for your exact truck. Factory figures are maximums, and the dash service reminder comes first when it shows sooner.
WANT MORE POWER?
LML Duramax performance upgrades.
Staged builds, lift pumps, transmission, exhaust and suspension upgrades for the LML Duramax.
BUYING A LML DURAMAX?
Get it inspected before you buy.
Our Diesel Pre-Purchase Inspection checks the engine, fuel system, transmission and front end, and looks for signs of past problems. We meet you at the seller.
How mobile service worksTell us your truck and where it is, we diagnose on site, you approve a written estimate, and we fix it where it sits.
See how it works →PLAIN-ENGLISH GLOSSARY
LML Duramax terms, explained.
- LML
- The 6.6L Duramax used from 2011 to 2016.
- CP4.2
- The LML’s high-pressure fuel pump, known for failures.
- CP3
- The older, tougher pump used on earlier Duramax engines; a common replacement for the CP4.
- DEF
- Diesel exhaust fluid. Sprayed into the exhaust to cut NOx.
- SCR
- Selective catalytic reduction. The catalyst that uses DEF.
- NOx sensor
- Measures emissions so the truck can dose DEF correctly.
- DPF
- Diesel particulate filter. Traps soot in the exhaust.
Name-brand partsWe install proven brands like Banks, S&S, FASS, Mishimoto, Edge, PPE and Bilstein.
See all the brands we install →OWNER QUESTIONS
LML Duramax questions, answered.
Will my LML’s CP4 pump fail?
Not every one does, but failures are common and expensive. A CP3 conversion is the best insurance if you plan to keep the truck.
Is the CP3 conversion legal?
Yes. The S&S kit we install is 50-state legal, keeps your emissions equipment and needs no tuning.
My truck says “Service DEF.” What now?
Don’t ignore it; the truck will slow itself down. Call us and we’ll find the failed heater, pump or sensor.
Why don’t you list prices for these repairs?
Every truck is different. Mileage, past repairs and how it’s used all change the parts and labor. Call us at 520-990-1033 and we’ll give you a straight quote.
What warranty do repairs have?
Repair labor is backed for 1 year or 12,000 miles, and new parts carry their manufacturer’s warranty. Warranty details →
LET’S TALK ABOUT YOUR TRUCK
Call, text or request a quote.
Tell us your year, mileage and what you want done. We’ll recommend the right repair, quote it and come to you.