09 Most Common LLY Duramax Problems and How to Fix Them

In 2004, Duramax introduced the second generation of its engine, the Duramax LLY.

At its time, it was a powerful 6.6L V8 engine.

At the time, it was a game changer for GM, but it has some common issues.

Today we’ll talk about common Duramax LLY problems.

LLY Duramax Problems, Symptoms and Solutions

There are 9 most common problems associated with Duramax LLY.

The topic deserves a more detailed discussion, so let’s get started.

01. Head Gasket Failure

The head gasket problem is one of the common complaints about Duramax LLY.

This problem is primarily caused by 02 reasons.

Reason 01: Huge Turbocharger

Duramax LLY is famous for its huge turbocharger, which provides superb horsepower and performance.

But this turbocharger becomes the main reason for gasket failure.

Because the huge turbocharger increases wear and tear in the head gasket, leading to failure.

Reason 02: Overheating

Duramax LLY overheats more frequently than other Duramax diesel engines.

Compared to the high-flow turbocharger, the Duramax LLY cooling system is insufficient.

This causes the engine to overheat.

05 Symptoms of a Blown LLY Head Gasket

  1. Low coolant level
  2. Engine overheating
  3. White smoke
  4. Rough idle
  5. Oil contamination

How to Check for a Blown Head Gasket

  • Radiator pressure test
  • Insert the test tube
  • Start the truck on idle
  • Sit and idle again for 03 to 05 minutes
  • Check the oil cap
  • Take the cap and rock it back and forth
  • Pull the rest of the pressure off

Solution to Blown Head Gasket

Replacing the head gasket is costly, costing you around $1000 to $1500.

So firstly, you can try the following tricks for an inexpensive and quick result-

  • Remove thermostat
  • Flush the cooling system
  • Add water to the system.
  • Keep the engine idle and slowly add a head gasket sealer to the radiator. (There are many types of head gasket sealers available in the market.
  • Keep the engine idle for 50 to 55 minutes
  • Install the radiator cap
  • Drain the cooling system completely
  • Install a brand-new thermostat
  • Refill the system with the appropriate amount of coolant.

I hope it will solve your gasket problem.

If the problem is not solved, take the vehicle to a qualified mechanic for proper treatment.

02. Turbo Inlet Manifold Issues

The turbo inlet manifold is an engine part responsible for airflow distribution into the cylinders.

Duramax LLY had a bad reputation for cracking and breaking turbo inlet manifolds.

High-speed driving wears down the turbo inlet manifold and causes it to break.

03 Symptoms of Bad Inlet Manifold

  1. Misfiring engine
  2. Difficulty in accelerating
  3. Leaking coolant

Solution to the Turbo Inlet Manifold Issue

Replacing the inlet manifold is the most effective solution to this problem.

It will not cost you very much.

03. Water Pump Failure Issues

The Duramax engine still suffered from water pump failure problems after the LB7 to LLY was upgraded.

Often, high mileage and plastic impellers are the main causes of water pump failure.

05 Symptoms of a Bad Water Pump

  1. Coolant leak
  2. Unusual noises
  3. Wash out the vehicle hood
  4. Engine overheating
  5. Rust and corrosion


If you notice any of the symptoms, you should take the vehicle to a repair shop for a proper diagnosis.

Replacement is the right option if your water pump lasts over 100,000 miles.

04. Overheating

Overheating is a common problem for any engine, and it is the same for LLY Duramax.

The Duramax LLY overheats when you stop and drive, like in traffic or if your vehicle carries a heavy load.

The poor cooling system of Duramax LLY (2004-2005) is also responsible for overheating.

05 Symptoms of Overheating

  1. Overheating light pops up
  2. Temperature gauge
  3. Clicking noise
  4. Steam
  5. Unusual smells


First, find out the actual reason for overheating in the following way:

  • Checking for leaks
  • Checking cooling fans
  • Checking fan motors
  • Head gasket leak test

If any of the above tests are problematic, they should be resolved.

This will fix the overheating issue.

05. Injector Harness Chafing

As Duramax LLY has been on the road for a long time, injector harness chafing issues are commonly reported by users today.

This problem decreases the vehicle’s performance and fuel economy.

04 Symptoms of Injector Harness Chafing

  1. Hard start
  2. Decreasing engine power
  3. Rough running
  4. Diagnostic trouble codes


A replacement of the chafing injector harness will be best for you.

By doing so, other problems can be avoided.

06. Bent Rods Issue

Duramax LLY suffers from this problem.

LLY rods are made from forged steel and designed as cracked caps.

Duramax LLY produces higher torque at low RPM, which causes increased pressure on the connecting rods and leads to bent rods.

500 RWHP is considered a danger zone for this problem.

05 Symptoms of Bent Rods

  1. Knocking sound
  2. Low oil pressure
  3. Damaged rod
  4. Low compression
  5. Seized engine


  1. Avoiding heavily modifying Duramax LLY is the simple solution. Because heavily modified engines produce up to 500 hp and bent rods.
  2. Replacing rods is another solution. But it is expensive and costs you around $3000-$4000.

07. EGR System Failure

The exhaust gas recirculation (EGR) valve recycles exhaust gases.

It increases Duramax LLY fuel economy.

In addition, it becomes a problem when it is filled with carbon.

As a result, the engine power is reduced.

05 Symptoms of Failing EGR

  1. Rough idling
  2. Poor accelerating
  3. CEL codes
  4. Misfiring
  5. Engine stalling


The simplest solution is using a throttle body cleaner to clean out the carbon build-up in the valve.

If there is a major problem with the EGR, it should be replaced.

08. Glow Plug Problems

Like most diesel engines, Duramax LLY uses glow plugs to increase fuel economy.

But unfortunately, in colder weather, LLY glow plug failing is very common.

04 Symptoms of Bad Glow Plug

  1. Hard to start
  2. Misfiring
  3. Poor idling
  4. Check the engine light


GM fixed this problem by re-programming, which is good news.

If you find a glow plug problem in your engine, just re-program it or take the vehicle to the dealership to check whether it was re-programmed.

09. Absence of Fuel Lift Pump

A fuel lift pump helps the engine to operate efficiently by delivering fuel at the correct pressure.

The Duramax LLY engine comes without a factory fuel lift pump.

Since the fuel lift pump is not available in the LLY engine, the CP3 injection pump does lift fuel pump work.

But it increases wear and tears on the injection pump.


Adding a replacement fuel lift pump is the most effective solution.

It is cheaper and easy to install.

Final Thoughts

You now have a better understanding of Duramax LLY issues, symptoms, and remedies.

As far as Duramax LLY is concerned, none of these issues are a major concern.

So, do not worry about your Duramax LLY if you own one.

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