What Scanner Do I Need For A Duramax? GM mechanic says…


Working on a Duramax is not for the faint hearted, but you already know that. I’m a GM trained technician and I’ve worked on a ton of Duramax trucks. Most days I love them, but some days…. aghhh …they make me so grumpy.

The best scanner for a Duramax is the Autel MaxiCOM Mk808. The MaxiCOM performs simple tasks such as resets, read and clear fault codes, reads live data such as injector balance rates. Command activate components such as EGR, Rad fans, Glow plugs, DPF regenerations and much more.

In this post you’ll learn why I like the Autel MaxiCOM scanner for the Duramax, you’ll also learn some of the common issues I met as a Duramax mechanic working at the dealership.

What You Need From A Scanner

Duramax is a no nonsense get her done kind of engine, and in my experience the owners tend to be of a similar build – hard working, DIY, salt of the earth, no BS, get her done types.

Tools that are up to the job are important. At the dealership I used the bullet proof GM Tech2 handheld scanners for the older trucks, the newer vehicles we used the wireless MDI system.

The old GM Tech 2 scanners were tough, no doubt about it. I witnessed an apprentice test drive a truck with a Tech 2 trailing from the door jam. Nice!

But the problem with the old Tech 2 is they were clunky and slow to use, the new MDI system is great, but it’s a laptop/desktop based system with wireless interface and spendy to buy.

The tool I recommend for your Duramax is the Autel MaxiCOM MK808, it’s very capable, does everything you need it to do, it’s robust and easy to use. Now, if you simply want to read powertrain fault codes, that’s fine, Autel has a reader for that too.

You can check out both scanners here on the Mechanics tools page.

Why I recommend the Autel

The Autel MaxiCOM is way more than a simple code reader. It’s capable of doing close to 95% of what I could do on the Tech 2 at the GM dealer.

I like the Autel for 4 simple reasons:

  • Strong and reliable – I’ve been using them for years and have yet to break one
  • Easy to use – Hook up and finds your vehicle automatically, color touch screen with big big clear buttons
  • Range of functions – It reads codes and live data on all systems not just the powertrain. Resets service intervals, activates components for testing, codes injectors, keys, performs relearn procedures for transmission, throttle etc. code new battery, performs DPF regeneration and a ton of other good stuff.
  • Range of vehicles – Works on nearly all vehicles, new and old and that’s important. It means you can work on multiple family vehicles without buying another scanner.

Common Duramax Problems

The Duramax engine is a serious thought unit, but it does have some weaknesses and like all motors it needs love from time to time. In our dealer workshop, the harder working Duramax engines were actually less trouble.

The most problematic Duramax tended to be the barely worked school run truck. They would typically come in with blocked EGR cooler issues or DPF and SCR issues. sensor issues.

Your Duramax is a great engine, well designed, tested and fit for purpose. However, use caution if tuning the motor. I’ve worked on a few coal burners and it hasn’t ended well. I’ve stripped motors with cracked pistons and broken cranks, these are expensive failures that could have been avoided. 

That said, here’s some common Duramax problems I would regularly see. Some issues are very common and as a Duramax owner you may already be familiar with one or two of them.

The Autel MaxiCOM will be invaluable diagnosing and repairing these type Duramax issues. You can check out the MaxiCOM along with a ton of other tools here on the Mechanics tools page.

The most common failures include:

  • Injector failure
  • Fueling issues
  • Head gasket failure
  • Water pump failure
  • Egr cooler failure
  • Fuel pump failure
  • SCR system faults
  • Manifold faults
  • Engine harness failure

Fuel Injector Failure

Fuel injector leaks internal and external. That’s really not unusual,  having the tools to accurately diagnose the root cause of the fault is crucial to nailing the repair first time out. Incorrectly calling failed parts on these trucks can be expensive, a single injector alone can cost $400 plus. 

But not finding a leaking issue can be even more expensive, a leaking injector will dilute the engine oil and possibly cause a catastrophic engine failure.

Running an injector balance rate test is easy with the Autel. The balance rate is a measurement of fuel delivery across all injectors. A large difference between the cylinders means you likely have an injector issue.

Injector issues are common across the LB7 and LBZ engines.

Fueling Issues

Most Duramax don’t employ a lift pump also known as a low pressure pump to move diesel from the fuel tank to the high pressure pump. This commonly contributes to fuel starvation issues when the fuel filter housing seal lets go and allows air sneak in.

Water pump failure

Water pump leaks are common too, across all the engines. But replacing a water pump is a maintenance issue with all engines. But with these big V8 we need to be careful of overheating the motor especially when towing.

Faulty fans and dirty clogged up radiator are common causes of overheating too.

Head Gaskets Faults

Blown head gaskets especially tuned engines. The gasket commonly fails across the back of the motor at the firewall where exhaust heat increases gasket stress.

EGR cooler failure

EGR cooler leaks are a motor killer. The EGR cooler can fail allowing coolant to enter the intake and into the motor, this doesn’t end well. Keep a sharp eye on coolant levels, investigate coolant loss immediately.

Replacing the pump may not be the end of the expense, metal filings from the pump are distributed throughout the fuel system – rail, injectors and it can cost a packet to put right.

SCR system faults

The system is designed to make our world cleaner…well it certainly made GM technicians a touch grumpier. The system was fraught with issues from NOx sensor failure to DEF fluid freezing, DEF pump and fluid level sensor failure.

The Mk808 unfortunately does not command test SCR heater circuits.

Fuel pump failure

High pressure fuel pump failure is uncommon with the exception of one pump, the Cp4 Bosch pump fitted to LML engines. It’s particularly prone to granding, lack of lube, usually poor quality diesel.

Engine harness failure

The V8 vibration has a knack of chafing the wiring harness loose and eventually rubbing a wire and shorting to chassis ground. Engine bay real estate is tight in a Duramax, harness rubbing is not unusual as no matter which path a loom takes, it’s never far from a chafing hazard.

Motors that have had major work seem to be more prone to chafing as looms may not be secured or routed correctly.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of classic car ownership, from tires to roof aerials and everything in between.

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