13 Most Common 6.6 LLY Duramax Problems(You Should Know)

Duramax LLY engines are some of the most powerful diesel engines on the market. They offer a lot of power and can go for miles without needing tuning or repair. 

However, like all machines, they do experience problems over time. To help you identify what to look out for before it becomes an issue, here are 10 common LLY Duramax problems that everyone should know about!

Certain LLY Duramax models have some common problems like turbocharger problems, oil filter problems, and glow plug control module issues. LLY Duramax engines are also known to blow head gaskets for certain models of the LLY Duramax engine. But all of these problems can be easily solved by an LLY Duramax certified mechanic!

Most Common Problems With 6.6 LLY Duramax:

Despite LLY Duramax being some of the best diesel engines on the market, they are not perfect. Many LLY Duramax engine owners have reported that LLY Duramax engines have experienced certain problems over time. 

There are so many LLY Duramax models, it’s hard to say which ones are more prone to experiencing common issues than others. However, here are the most common problems with LLY Duramax engine owners have encountered-

1. Turbo Inlet Manifold Problem

The LLY Duramax turbo inlet manifold is a part of the LLY Duramax engine that helps to ensure proper airflow. This component has been known to crack and break due to regular wear and tear, especially if you’re driving at high speeds for long periods of time or driving on rough roads often.

When this happens, LLY Duramax engine owners have noticed that their engine does not perform as well. This is because the LLY Duramax turbo inlet manifold helps to deliver air into the LLY Duramax engines. Without this component working properly, LLY Duramax LLY engines are less likely to reach maximum power output and fuel mileage will be less efficient.

2. LLY Duramax Engine Throws Codes for No Reason

Another common LLY Duramax problem engine owners have noticed is that LLY Duramax LLY engines throw error codes randomly, even though there’s nothing wrong with them!

This issue occurs because the LLY Duramax ECM (computer) can detect a problem before it occurs and LLY Duramax LLY engines will throw an error code to alert you of this. It is common with many diesel engine owners, as LLY Duramax LLY engines are designed to operate without problems for long periods of time before needing repairs or tuning.

For example, the LLY Duramax LLY engines may throw an error code for a dirty injector before it actually becomes clogged. By getting the LLY Duramax LLY engine serviced at this point, you can avoid future problems with your LLY Duramax LLY engine!

3. Head Gasket Failure

Some Duramax LLY users also complained of experiencing head gasket failure. This occurs when the LLY Duramax LLY engine overheats and coolant seep into the combustion chamber.

The LLY Duramax LLY engine will need to be taken apart and repaired, which is a costly process that can cost thousands of dollars. LLY Duramax LLY engines with head gasket failure will need to be repaired immediately, because the LLY Duramax LLY engine could potentially overheat and cause more damage than you can repair!

4. Clogged or Dirty Fuel Filter

As diesel fuel filters do not have a filter in them like gasoline vehicles, it is common for Duramax LLY engines to clog or get dirty over time. When LLY Duramax LLY engine owners notice that their fuel filter stops up frequently, they should have it replaced right away- even if there are no signs of problems with the LLY Duramax LLY engine!

5. Chafing Injector Harness

Another LLY Duramax LLY engine problem that is common but not talked about much is injector harnesses. These can chafe or rub against the LLY Duramax LLY engine, which damages them over time.

This will cause LLY Duramax LMY engines to stop working properly and eventually start experiencing fuel efficiency issues as well! If you notice that your vehicle’s power has decreased significantly recently, it may be because of a damaged or chafed LLY Duramax LMY injection harness.

6. Engine Knock at Idle

A knock-in of an LLY Duramax diesel engine when idling could indicate problems with the camshaft timing system. The noise should decrease once underway if this is true.

If the LLY Duramax LMY engine knock persists, there may be damage to valves or pistons. If this is true, you will need to have your LLY Duramax LMY engine repaired at a local service center.

7. Water Pump Failure

One LLY Duramax LLY engine problem that can lead to a vehicle breakdown is the failure of the water pump. This occurs when coolant fails and causes your LLY Duramax engines to overheat, which will cause damage if not addressed immediately!

If you notice that your LLY Duramax engine’s temperature is increasing more quickly than usual, it may be time for an inspection of the water pump as well as other components such as hoses and fan belts (if equipped).

8. Loss of Power on Acceleration

The most common issues with an LLY Duramax diesel truck are loss of power at low revs under load and lackluster performance. This causes LLY Duramax engines to have issues accelerating, which can be dangerous.

You should pull over if you are losing power on acceleration or notice that your LLY Duramax LMY engine is having trouble powering the vehicle. These could indicate transmission failure as well- so either way, it’s best to get out of traffic and take care of the issue!

9. LLY Duramax Overheating Issues

Overheating is a common problem for any engine, and the LLY Duramax isn’t an exception. LLY Duramax engines may overheat when you drive in stop and go traffic, or if your LLY Duramax engine is loaded down heavily.

This can cause damage to your LLY Duramax LMY engine’s pistons and rings, which means you will need a repair sooner rather than later! If you notice that the temperature gauge on your dashboard has been climbing higher while driving without any other symptoms of overheating (increased coolant loss perhaps), it may be time for a tune-up at a local service center.

10. Lackluster Fuel Economy

Another common problem with LLY Duramax engines is lackluster fuel economy. You may have noticed recently that your vehicle seems to use more gas than usual- when idling! This could lead to LLY Duramax engines having problems accelerating and could mean that your LLY Duramax LMY engine needs a tune-up.

Another reason for having a lackluster fuel economy is the LLY Duramax engine’s MAF (mass air flow) sensor. If the LLY Duramax LMY engine is losing power after driving for a while, this could mean that it has to work harder than usual- which means more gas!

11. LLY Bent Rods Problem

One LLY Duramax LLY engine problem that can be life-threatening is the LLY bent rods. The LMY Duramax diesel engines use seven cast iron LYH crankshaft style connecting rods, which are held together by a web of forged steel (in place of cast aluminum like before).

The cracking and breaking of these could cause the pistons to hit valves in your LLY Duramax LMY engine’s cylinder head at high speed! This will either result in major damage or possibly an explosion if it doesn’t break anything first. If you notice any knocking noises coming from under your hood, please take care of this as soon as possible.

12. EGR Valve Failure

LLY Duramax engines include an EGR (exhaust gas recirculation) valve that recycles exhaust gases back into the combustion chamber. The LLY Duramax engine uses this to lower emissions and increases fuel economy, but it can become a problem if carbon builds up on the valves or in the turbocharger’s intercoolers.

This causes your LLY Duramax engine to lose power- which means you need repairs as soon as possible! This could also cause damage from lack of air getting into cylinders, which will mean it needs more than just a tune-up.

13. Glow Plug Failure

The LLY Duramax engine also includes glow plugs that help startup and increase fuel economy. Unfortunately, these can fail or become damaged over time- especially if your LLY Duramax LMY engine is exposed to cold temperatures often (like in the winter).

You could notice a loss of power from your LLY Duramax engine during acceleration, as well as it not starting up quickly when you need heat! It’s best to have this looked at by a professional so they can address any other problems that might be causing issues with your vehicle.

General Pros And Cons Of LLY Duramax

Reading about this many common problems about the LLY Duramax engine can be discouraging, but there are many benefits to LLY Duramax LMY engines. I figured out more pros than cons of using this engine upon research, which makes this engine an excellent choice for trucking!

Here are the pros & cons of the LLY Duramax engines:


  • LLY Duramax engine is extremely powerful, especially when compared to other trucking options! It can tow and haul heavy loads easily.
  • LLY Duramax engines are fuel-efficient for trucks, saving you money on gas costs in the long run.
  • The LLY Duramax engine is reliable and durable- having been around for almost two decades!
  • The LLY Duramax engine is also easy to repair and maintain, giving you more time on the road than sitting at a shop.
  • The design of the LLY Duramax is indeed splendid, which makes it an excellent choice for trucking.
  • Smooth operation even if you’re carrying a huge load, the LLY Duramax engine can easily handle any huge workload.
  • Very low emissions and better fuel economy than other Duramax LLY diesel engines on the road!


  • The LLY Duramax LMY engine has had issues with turbocharger failure in the past- making it less reliable for some people.
  • These engines can require frequent tune-ups and repairs, especially if you don’t take care of them regularly.
  • Even with LLY Duramax LMY engines being known for their strength and durability they can still break down over time- just like any other vehicle!

Customer Reviews On LLY Duramax Engine

Just like me, other LLY Duramax owners seem to love their engine! Although they complained about a few minor problems just as I mentioned, they are satisfied with the overall performance of LLY Duramax engines. Here are some user reviews that will help you decide if LLY Duramax LMY engines are the right fit for you:

  • “Love mine, no major problems so far after 80k miles. Only wish I had the 6-speed tranny.”
  • “Very happy with my 05 which I use mostly for towing. In my opinion, the 05’s with the 5 spd Allison tows better than the 6 speeds. My buddy who has an 06 says his tranny is shifting up and down while towing, while my 05 holds 5th gear without a problem. Any issues that the 05’s might have I’ve upgraded to be on the safe side, as far as head gaskets I’m not concerned with only 80K on the odometer. Where I work (Large Hospital) There are at least 10 Duramax’s (LLY’s) with over 100K some with over 200K and none have had a head gasket problem. Quite a few are running tuners as well.”

Final Thoughts

Although LLY Duramax LMY engines have had issues in the past, they are improving over time. These common problems with LLY Duramax can be fixed easily by a professional if you know where to take your LLY Duramax LMY engine for repairs!

I hope this blog post helped answer any questions about LLY Duramax that you might have. If not please feel free to leave them below and I will get back to you as soon as possible. Thank You!

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