Duramax LBZ Engine Problems

The 5 Most Common Duramax LBZ Engine Problems

Jake Mayock

Meet Jake

Jake is a founder of 8020 Media and has been creating automotive content online since 2017. He has been the lead writer for Chevy Trucks and has transformed it from the old and outdated site it was into what it is today. Jake creates a ton of GM related content for the 8020 Media YouTube channel and specializes in Duramax and Vortec information but has a wealth of knowledge across all GM cars and engines. Jake believes the L5P is the best diesel on the market today.

The LBZ Duramax is, still today, the favorite Duramax of diesel enthusiasts and one of the most sought after engines. The LBZ was upgraded to be able to handle more power than the previous Duramax and to improve reliability.

Furthermore, the LBZ has limited emissions equipment, preventing major problems that newer diesel engines face. The performance potential, strong reliability, and lack of emissions equipment are what make this engine so desirable.

The LBZ got a stronger block and forged rods to fix problems with the previous LLY. Despite its improved reliability, the Duramax LBZ is still prone to a number of common problems such as cracked pistons, water pump and glow plug failure, transmission line leaks, and EGR valve issues.

Duramax LBZ Engine Problems

  1. Cracked Pistons
  2. Water Pump Failure
  3. Glow Plug Failure
  4. Transmission Line Leaks
  5. EGR Valve Failure

If you would rather consume this content via a video, check out our Chevrolet LBZ Duramax Common Problems video below:

1. Cracked Pistons

The LBZ is revered for its tune-only performance capabilities. With various upgrades, this engine is easily capable of producing over 600whp and 1,000lb-ft. of torque. However, one common failure point on tuned engines is cracked pistons.

This “common problem” is really only common for folks pushing serious power. The pistons on the LBZ are generally good up until around 600whp, levels beyond that are when piston failure becomes imminent. If you plan on keeping your engine purely stock, you can ignore this problem. While the pistons have cracked before on totally stock engines, it’s highly unlikely and rare.

Duramax strengthened the block and lower half of the LBZ to handle to stock performance increases over the previous LLY models. However, the pistons remained the same, produced purely from cast iron which is why they are prone to cracking at serious power levels.

Cracked Piston Prevention Options

If you are looking to produce serious power, you’ll need to open your wallet. And your engine. To prevent piston failure, your only option is to either not tune your truck or to upgrade the pistons and probably the rods to something forged.

2. Water Pump Failure

The water pump on any vehicle generally functions the same way. The pump is responsible for pushing the engine coolant throughout the cooling system to prevent the engine from overheating. On the LBZ, and all Duramax engines for that matter, the impeller inside the water pump is made of plastic. The impeller is like a little rotating fan that is responsible for actually forcing the coolant through the system.

If your impeller breaks or goes bad, the coolant won’t flow through the engine – and unfortunately the impeller on this water pump is made of plastic. Over time this plastic wears down leading to water pump failure which commonly occurs every 80,000 to 100,000 miles.

Water Pump Failure Symptoms

  • Engine overheating
  • Leaking engine coolant
  • Frequent low coolant warnings / refills
  • Water pump is making weird squeaking noises
  • Steam coming from the radiator

Replacement Options

Solving this issue is generally pretty simple. If you continue to replace your water pump with an OEM pump that has the plastic impeller, expect to continue replacing it every 80k-100k miles. Alternatively, you could upgrade to an aftermarket pump that has a billet/aluminum/iron/etc. impeller on it to guarantee that you won’t have to be replacing it again anytime soon.

Aftermarket pumps are probably an extra $50-$100 but the replacement cost is the same and the added reliability is totally worth it in my opinion.

DIY Guide: https://www.dieselworldmag.com/diesel-technology/dmax-tig-welded-water-pump-2/

3. Glow Plug Failure

In 2006 year models, both the LLY and LBZ Duramax engines had glow plug failure issues. The glow plugs are powered by a glow plug control module which sends the electrical current to heat them up.

2006 year models also had a control module issue in which the module was known to overload the plugs with current, causing the tips of the glow plugs to actually break off. If the tip breaks off, you now have a piece of metal flying through your engine that can cause serious damage.

Glow Plug Control Module Fix

Fortunately, this problem was caused by the programming of the control module. Fixing this issue was as simple as having your dealership reprogram the control module. While this issue was common in 2006 LBZ models, if you are considering buying one today this shouldn’t be of any concern as the problem was fixed long ago. Simply confirm that the module had been reprogrammed back in the day.

Glow Plug Failure Symptoms

If you have the issue with the control module, you probably won’t be running into many of these symptoms. However, I wanted to provide some common symptoms of normal glow plug failure. Glow plugs are pretty cheap and easy to replace so I recommend refreshing with a new set if you have any of these symptoms:

  • Hard starting / difficulty starting (especially in cold weather)
  • Rough idling
  • Cylinder misfires
  • Glow plug engine light
  • Black smoke coming from the exhaust

4. Allison 1000 Transmission Line Leaks

While the Allison 1000 transmission is one of the best diesel transmissions out there, the tranny cooler lines used by GM had some design flaws.

The cooler lines on the Duramax LBZ have a design fault at the “crimp” to where the crimp isn’t suitable enough to hold onto the line and prevent fluid from leaking. Leaks are most common when the fluid is cold and on trucks running high idles. Some folks have a consistent leak while others tend to only leak when the engine is cold.

Fluid leaks are important to catch early as running low on fluid can cause catastrophic damage to the transmission. If you are leaking you will notice red fluid dripping from underneath the engine bay. This issue is extremely common and can occur as frequently as every 20,000-30,000 miles.

The best replacement options here are to upgrade to more durable aftermarket transmission lines.

5. EGR Valve Problems

While the LBZ is one of the last engines lacking serious emissions regulation systems it was still equipped with an Exhaust Gas Re-circulation system, known as an EGR.

The most common EGR issues are caused by the EGR valve. The EGR valve is prone to building up gunk and becoming clogged, restricting the amount of airflow which then enters the engine and altering air to fuel ratios. The valve can also become stuck closed or stuck open which is what can cause significant performance issues.

Failing EGR Valve Symptoms

  • Rough idle
  • Sluggish performance
  • Cylinder misfires
  • Engine stalls while idling
  • CEL for EGR or lean/rich AFR codes
    • (P0401, P0404, P1404, P0405)

A lot of LBZ owners will essentially block out or delete the EGR itself. Completely removing the EGR is going to be slightly more expensive and complicated than blocking it. Either option should be sufficient in solving these problems. You will get CEL’s for doing either of these but they can be coded out with a tuner – just keep in mind you will not pass emissions testing with this done.

Duramax LBZ Reliability

Unless you are looking to break the 600rwhp barrier, the Duramax LBZ engine is extremely reliable. The tune-only power capabilities combined with its reliability are what make the LBZ the most sought after Duramax today, nearly 14 years after it stopped production.

With a strengthened block and good internals, the LBZ is easily capable of surpassing the 300,000 mile mark with sufficient maintenance and care.

Throughout the course of ownership you’ll probably have to replace a water pump or two and upgrade your transmission lines. Outside of these small things, you’re really only left with standard maintenance. These are really the only two common problems I would consider these engines to have as pistons are only a problem at high HP, the glow plug module should have been fixed, and the EGR can be deleted to remove any potential problems there.

One other worthwhile reliability factor to mention is the Allison 1000 transmission itself. Great transmission, however, it is only capable of handling an additional ~100hp or so before it will need to be upgraded and rebuilt. Just something to consider if you are intending on dropping more than a tune and a few bolt-ons onto the LBZ.

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  1. I have a 2006 GMC 2500HD SLT with the LBZ Duramax, all stock except I removed the EGR valve about 10 years ago. I now have the CEL on and can’t seem to do anything to get it off. It’s been on for a number of years now, and I’ve replaced the air filter element, the mass flow sensor and cleaned them all, but still can’t get the CEL to go off. I’ve now ordered a new fuel tank cap thinking that it may do the trick.
    Years ago I installed an additional tank in the truck bed and ran the lines up to the engine so I could burn straight vegetable oil (SVO). That worked well and I have used it for over 50,000 miles, but now I’ve had some difficulty getting SVO for the last couple years. Presently I’m running on just diesel fuel. The SVO kit is one I bought from Golden Fuel Systems about 12 years ago and have it hooked to a 60 gallon Trekker tank, a Racor FH100 filter, thru a FASS fuel pump, thru the two GFS 3-port return/supply valves, and then thru the stock fuel filter. A 3-pole rocker switch allows me to switch to running on SVO, or back to diesel fuel.
    Can you offer any help with getting the CEL to go off?

  2. I have an 07 duramax that is called a classic. It is a 3/4 ton. I have a noise that is coming from underside of the pick up I think. It is a squeal or a growl and I have had it to two different shops to have them look at it, to no avail. They can hear it also but do not know what it is.
    Any help on this issue would be greatly appreciated.

    1. Check the exhaust on the passenger side and you will find a weld break near the bracket by the ring exhaust clamp. Drove me nuts hunting that cannery singing under my trk. 5 minutes with a mig welder and it was gone.

  3. I have a 2002 Duramax I bought brand new I’ve pulled a work trailer with it for nearly 20 years it gets nearly 20 miles per gallon best truck I’ve ever had also have an 08 duramax

  4. I have a 2007 lbz on my 3500, I have never experienced anything like what you describe. The only thing I have ever had was a rear brake line break off at the coupling after the abs (corrosion). After a particularly hard breaking to avoid an impact with another car ( Dotson b210). WOULD HAVE BEEN UGLY. Anyway I have 233,000 on the truck, only upgrade is a tunner (extreme) that stays in the extreme setting 24/7 and glows upgraded + 100 deg for colder weather.
    Lucy i guess. All regular maintenance otherwise.

  5. Looking into getting an 07 lbz wanted to know if their was anything to check for when I go look at the vehicle before deciding on purchasing.
    Has 83,000 miles. Would appreciate a heads up thank you.

  6. I have a 06 just started smoking black smoke and died was always running fine on it won’t even idle and help on it

  7. 06 gmc 4500 6.6 49k miles It is now runny rough and sometimes I hear a knocking sound. check engine light and Trans slight . the diagnostic are P2152 and U1096 when checked no visible damage, what do you think?? thank you,Art

  8. We havent had many LBZ’s come through our workshop, but of the ones we’ve had, the majority of issues have been either cracked pistons or leaks in transmission lines. 100% agree with what you guys have experienced. Great job getting the info out, we’ll be referring customers to this article from now on.

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