5 Most Common LML Duramax problems | Easy Fixes

Duramax LML is a powerful and steadfast engine that has been used in many different types of vehicles. However, there have been some reports of engine problems with this model.

One of the most common LML Duramax problems appears with the injection pump. It can cause a loss of power and performance; in some cases, the engine may stall. Other reported issues include leaky EVAP system and EGR cooler, emissions problems, and DEF system issues. 

While these issues can be frustrating, they are somewhat less complicated to fix and should not deter you from considering a Duramax LML-equipped vehicle. Hence, in this article, we’ll look at these five most common Duramax engine problems and what you can do to fix them.

Which Cars Model Has LML Duramax Engine? 

A few different cars have the 6.6L V8 Duramax LML engine. The most popular models are the Chevrolet Silverado and GMC Sierra. Let’s look at the specific models of these cars that have the LML Duramax engine.

2011-2016 Chevy Silverado HD

Chevy Silverado HD is a top choice for the heavy-duty (HD) pickup trucks, and the 2011-2016 models come with the LML Duramax Engine. 

It is built on a sturdy frame designed to withstand heavy loads and features a powerful suspension system that can handle rough terrain. 

2011-2016 GMC Sierra HD

GMC Sierra HD from the 2011-2016 year models is rigged with the LML Duramax Engine. 

This heavy-duty workhorse engine is known for high output and durability, making it the ideal choice for those who need a reliable and capable truck for work or play. 

What Are The Signs Of LML Duramax Issues? 

Duramax LML is one of the most forceful and versatile engines today. Nonetheless, like all engines, it does have some problems as well, and the common symptoms of those problems are:

  • Misfires of the cylinders
  • Rough idling
  • Defective sensor
  • Poor DEF quality
  • Insufficient performance

5 Most Common LML Duramax Problems?

It’s no secret that the LML Duramax engine has had its fair share of problems. Many truck owners have experienced major issues with their trucks, and most of these problems seem to be fairly common. 

The good news is there are some things you can do to help prevent these problems from occurring or at least minimize their impact. 

Here are the five most common LML Duramax problems, the after effects, and what you can do to avoid them:

1. CP4.2 Injection Pump Failure

The CP4.2 injection pump is a high-pressure, common fuel system introduced in 2011. However, it has been known to fail, causing several engine problems like decreased fuel effectiveness and creating emissions.

What happens

The possible problems that can happen due to a failed CP4.2 injection pump are a loss of power and an inability to start the engine. 

Other issues include excessive smoke, hard starting, rough idling, and increased fuel consumption. In some cases, the situation can be severe enough to cause the engine to stall.

How to Fix CP4.2 Injection Pump Failure on LML Duramax

The good news is you can take steps to fix the problem and avoid future failures. First, check the wiring harness for any frayed or broken wires. If you find any, change them with new ones. Next, inspect the fuel lines for any leaks to repair or replace them.

Finally, examine the LML Duramax injectors for any wear or damage. Whether there is any, restore them with new ones. 

In a critical case, You may have to replace the whole pump, which can be expensive, but it’s worth the investment to keep your Duramax engine running smoothly.

2. Leaky EGR Cooler

If you’re the owner of a GMC or Chevy Duramax diesel truck, you may be all too familiar with the EGR cooler leakage problem. 

It is responsible for recirculating exhaust gases into the engine to reduce emissions. However, an EGR cooler can develop cracks and leaks over time, which can cause coolant to mix with the engine oil and harm the engine. 

What happens

It can lead to problems, including decreased engine execution, increased fuel consumption, and potentially serious engine damage.

How to Fix Leaky EGR Cooler on LML Duramax

The best way to solve this problem is to have the EGR cooler replaced with a new one made of steel. It will require some engine disassembly, but it is a relatively straightforward process.

3. DEF System Issues

Another common problem with the LML Duramax is a problem with the DEF system. DEF, or diesel exhaust fluid, is used to help recede emissions. When the DEF system isn’t working properly, it can cause various problems.

What happens

The engine will go into “limp mode” when there is a problem with the DEF system. It can cause a loss of power and fuel economy, which can be very frustrating for drivers. 

It can also cause the engine to misfire or run roughly. These problems can be very damaging to the engine and can cause a lot of costly repairs.

How to Fix DEF System Issues On LML Duramax

In some cases, the DEF system may need to be completely changed. Other times, a simple software update may be all that’s needed to fix the problem. 

4. EVAP System Leaks

EVAP system is responsible for capturing and recycling fuel vapors and uses various sensors and valves to do this. Unfortunately, these components are prone to failure and create the issue.

What happens

Leakage in the EVAP system can cause fuel vapors to escape. It can result in a loss of power, reduced fuel economizing, and a check engine light. 

How to Fix EVAP System Leaks on LML Duramax

To fix the problem, the first step is to check for any obvious leaks in the system. If none are found, the next step is to perform a system pressure test. 

It will help identify areas where the system is not holding pressure. Once the leak has been located, it can often be repaired with a simple sealant. However, the entire EVAP system may need to be replaced in some cases.

5. Emissions Problems

One more common problem that owners of LML Duramax-equipped vehicles experience is what’s commonly referred to as “emissions problems.” In short, the engine is not burning all of the diesel fuel injected into the cylinders instead of sending raw, unburned fuel out the tailpipe.

What happens

The symptoms of this problem can vary, but they often include a check engine light or increased fuel consumption. In some cases, the problem may also cause the engine to run rough or stall. 

One of the root causes of this problem is often traced back to the exhaust gas recirculation (EGR) system. This system helps reduce emissions but can also cause buildup on the intake valves, resulting in the symptoms described above.

How to Fix Emissions Problems on LML Duramax

A few different things can be done to fix the problem. First and foremost, make sure that you’re using quality diesel fuel. 

It’s also a good idea to check the injectors for any signs of wear or damage. In some cases, simply replacing the injectors may be all that’s necessary. 

you can also check our guide on L5P Duramax Problems

How Much Does It Cost To Fix LML Duramax Problems? 

If you’re the owner of an LML Duramax, you may wonder how much it will cost to fix any problems.  However, if something goes wrong, the repair cost can vary depending on the problem. For example, a simple inspection may cost $600 on average ($300-low range and $1000-high range), including the inspection cost. 

While a more complex repair such as replacing the engine will cost around $15,000, with an extra $5,000 in labor-intensive. 


Here are some related questions that people often seek answer when they search for LML Duramax problems. We have also covered this questions and compiled at one place so that you can easily get all the related information related to Duramax LML engine.

Is LML Duramax A Good Engine?

LML Duramax is a 6.6-liter turbodiesel V8 engine that was first introduced in 2011. It replaced the older 6.6-liter LBZ Duramax engine and offered increased power and fuel efficiency. 

So, is it a good engine? Yes, it’s a reliable engine that offers increased power (LML Duramax hp 397), speed (maximum engine speed 3000 RPM), and fuel efficiency over its predecessor. 

Nevertheless, there have been some reports of issues with the injection pump and emissions system, so it’s important to do your research before making a final decision.

How Many Miles Will A Duramax LML Last?

In terms of longevity, the Duramax LML is a very reliable engine. Most of the owners have reported getting 200,000 miles out of their trucks. 

Proper maintenance makes it not uncommon for a Duramax LML to last for close to 300,000 miles. So if you’re looking for a diesel engine that will give you long-term reliability and performance, the Duramax LML is a great option.

How Common Is Cp4 Failure LML?

Cp4 Failure on LML Duramax is quite common. About 7% of all CP4s will fail on an LML Duramax.
The good news is that many aftermarket options are available to help prevent this from happening. One option is to install an aftermarket CP4 pump. It will help to ensure that your pump can withstand the high pressures.

How Do You Make LML Last?

LML Duramax is a workhorse of an engine, but like any engine, it needs proper care and maintenance to keep it running strong. Here are a few tips to help you get the most out of your LML Duramax:

  • Change the oil regularly
  • Use good quality motor oil.
  • Don’t forget about other fluids and additives.
  • Have your truck serviced regularly.


If you’re considering purchasing a GMC Sierra or Chevy Silverado with a Duramax engine, it’s important to know about the most common LML Duramax Problems for better ideas. 

Though, these problems are relatively minor compared to the engine’s overall reliability. The LML Duramax can provide years of trouble-free service with proper maintenance and care. 

Besides, most Duramax problems can be fixed somewhat easily and inexpensively. As such, the LML Duramax should be considered a sound investment for anyone in the market for a long-lasting and reliable diesel engine.

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