Duramaxes are generally pretty reliable, especially in stock form. Like all the other manufacturers, they do have some issues that you can expect to deal with over time. A few notes on them in general…Seats. They have the best seats in the business, period. If you are a long-haul kind of person, the Dmax seats are awesome. The ride quality of the Dmax is also second-to-none. The independent front suspension, although much maligned for off-roading and lifting, rides much better than any of the solid-axle setups from Ford or Dodge.
General Duramax Issues
The 2001-2011 Dmax trucks are all fairly similar in design and the general engine configuration is also pretty much the same. These trucks are all prone to fuel starvation/air in the fuel system issues. The trucks do not use a factory lift pump; the injection pump actually has to suck fuel from the tank, through the filter in order to run. For this reason, dirty or loose fuel filters, leaking water-in-fuel sensors or bad o-rings in the fuel filter housing can cause no-start conditions, especially hot.
Water pumps are also an issues with the Duramax. They have two weep holes and they are pretty hard to see, but the pumps are generally only good for 80-100k miles and they are very labor-intensive to replace.
Front wheel hub assemblies are also common failure items. This is especially true if you are running larger than stock tires or if you are offroading.
Tie Rod assemblies. They are notoriously weak and will snap in a heartbeat if you do a boosted launch in 4wd. There are some great aftermarket parts available from Cognito and others to solve this problem.
Idler/Pitman arms. The design of the steering linkage on these trucks will allow side-loading of the Idler and Pitman, causing them to wear out and get sloppy. It gets worse with larger tires. Again, Cognito makes a great kit the PISK (Pitman/Idler Support Kit) that prevents the side-loading and can keep you from having to replace expensive Idlers and Pitmans. These are a must if you have big tires.
2001-2004 LB7 Trucks
The LB7 trucks are the most prone to injector issues. These trucks actually had their injector warranty extended to 7 years/200k because of a design flaw in the injectors that causes premature failure. Newly designed injectors have been released by Bosch and have been lasting much longer. The injectors tend to have high return rates, which can kill performance and actually put the truck into limp-home mode. They also develop leaks through the nozzles, and this will show as smoke/haze at idle. If one of these conditions is noted, all 8 injectors must be replaced. The real downside of the LB7 trucks is that they are the most labor-intensive injectors to do, taking about 13 hours.
The LB7 fuel filter housings are the most expensive and also the most prone to failure.
These trucks have several monikers (LLY, LMM, LBZ, etc) but are all fairly similar in design. Isuzu changed the injector placement to make them much easier to change out, but Bosch’s newly designed injectors are much less prone to failure. Otherwise, these trucks share the same common issues.