The 6.6L Duramax LML (2011-2016) added DEF/SCR and switched to the Bosch CP4.2 fuel pump - the same pump that grenades on Ford 6.7L Powerstrokes. The LML makes 397 HP / 765 lb-ft and tows well, but CP4 risk and NOx sensor failures define its reputation.
The LML's biggest financial risk is the CP4.2 pump - one failure can total the fuel system for $10,000+. A $1,000 disaster prevention kit is mandatory if you plan to keep the truck.
Same pump as Ford 6.7L. When it fails, debris contaminates the entire fuel system - $10,000+ repair. A CP3 conversion kit ($2,000-$3,000) or bypass kit ($1,000) is standard.
Get a free diagnosis →The post-SCR NOx sensor is the #1 emissions failure on LML trucks. P229F or P20EE. Sensor cost $500-$850 installed.
View P20EE Diagnosis →The DEF supply pump and heater fail together. P20B9 or P208A. Replacement is $1,200-$1,800.
Get a free diagnosis →Hard winter starts on LML trucks trace to glow plug or controller failure. Easy fix at $300-$700.
View P0670 Diagnosis →LML EGR coolers crack at lower rates than older Duramax but still possible. Coolant loss, white smoke - check intercooler for residue.
Get a free diagnosis →Factory water pump fails around 150,000 miles. Coolant weep from the pump body. Standard wear-and-tear.
Get a free diagnosis →Run a free AI diagnosis tailored to your exact diesel. Get the most likely cause in under 30 seconds.
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GM TSB 14-06-04-002 updates SCR control software. GM customer satisfaction program N192275850 extends NOx sensor and SCR catalyst coverage on 2011-2016 trucks to 10 years / 120,000 miles. NHTSA 19V-396 covers 2019 trucks (L5P, not LML). GM never officially recalled the CP4 pump - bypass kits are aftermarket-only.
If you see a check engine light, these codes most often relate to the issues above. Click any code for full diagnosis steps.
Yes - it's the single best $1,000 you can spend on an LML. One CP4 failure can total the engine's fuel system.
Mostly. The block, heads, and Allison transmission are excellent. Emissions (DEF, NOx sensors) and the CP4 are the weak spots.
LML (2011-2016) makes 397 HP / 765 lb-ft and uses CP4. L5P (2017+) makes 445 HP / 910 lb-ft and uses a more reliable system.
300,000+ miles with proper maintenance, CP4 bypass, and emissions repairs along the way.
2015-2016 trucks are the most refined - mature emissions calibration and updated NOx sensor placement.
Illegal under the Clean Air Act, voids warranty, and prevents registration in most states. Don't.