Volume 2 Issue 3 - Diesel Articles

Duramax Power Mods and Your GM Warranty

As I started to gather material for this article about the affects of having a Duramax Power Chip or Duramax Power Programmer on your GM warranty, I was dealing with my first casualty arising from GM’s new approach to applying – and, as in my case, denying – its warranty policy. I was not happy about it. The incident involved a good customer, a failed engine and a powertune: that is, a modified engine calibration loaded into the Engine Control Module (ECM) that I had both engineered and installed.

In the past, GM has normally dealt with engine failures on a case-by-case basis. In doing so, it has traditionally been very fair in its approach. Engine overpower failures, that is, failures induced by a combination of customer abuse and huge power programs, are very well defined in a GM bulletin. It is much less difficult to face a customer and deny a warranty for a blown engine when we can show him exactly what happened, and why it is not GM’s fault. But what happens when an engine failure results from a source normally covered under the warranty and the owner has a chip or, as in my case, an aftermarket calibration loaded in the ECM?

As reported previously in maxxTORQUE, all Bosch Engine Control Modules installed in 2006 and later Duramax engines know whether the calibrations they contain have been modified – in any way – from stock. Even the cautious owner who only runs the lightest fuel economy setting in his Duramax will register an ECM change. Despite the fact that such a light power program change is unlikely to cause any damage to the engine, GM may have all the data it needs to refuse warranty coverage on a failed engine when it otherwise would have covered the repairs.

In such a scenario, any damage that occurs is likely to be caused by something other than the slight power modifications. For instance, if an injector starts flowing a little more than it should under a heavy towing condition with a large heat load then, sometimes, a piston combustion chamber will overheat, melting the aluminum and creating a hole from the combustion chamber bowl into the oil-cooling jacket. This almost always causes cylinder wall scoring from collateral damage, requiring engine replacement and at least one new injector to fix the problem. I found myself precisely in the middle of this awkward scenario.

The Investigation Begins

Whenever a failure like this occurs, a technician begins with normal diagnostic procedures. This engine was running reasonably well with no smoke: there was only a bit of roughness from a single-cylinder misfire. The trouble codes stored corroborated the misfire and pinpointed a cylinder. The technician who started the diagnostics ran through some typical checks and then performed a compression test. Noting little to no compression on the misfiring cylinder, he then had to tear down the engine in order to investigate the failure. Upon tear down, he found a hole in the base of the combustion chamber in the piston. Following GM procedures, he meticulously documented all of the damage in the engine. As is almost always the case, photographs were taken to provide evidence of the nature of the failure.

At this point, he reconnected the battery and checked the Calibration Verification Numbers (CVN) in the ECM. He found, as I knew he would, that one or more of the CVN were different from stock, indicating an aftermarket calibration had been installed. The CVN check is part of the process a technician needs to follow in order for GM to make a decision on whether or not they will authorize and pay for an engine repair for the truck. Seeing the CVN change, one doesn’t know exactly what calibrations have been changed or by how much, just that something has been changed. These numbers are reported to GM, along with all the other information gathered. For instance, was there oil coking on the bottom of all the pistons that indicates excessive heat from an over-aggressive powertune? Is there bearing fretting or unusual wear on the wrist pin? Is there polishing on the thrust side of the cylinder wall indicating fuel wash? Is more than one piston melted?

In this scenario, the only signs of damage were isolated to one cylinder and there was only one type of failure, with no other indications of an overpower failure. The root cause of failure in this particular scenario was a failed injector.

GM – Yesterday and Today

How would GM traditionally have treated a scenario like this? From my previous experience, GM more than likely would have approved the engine replacement and one injector under warranty and then given the customer polite but direct instructions regarding his aftermarket duramax power programmer. Something like,

We recognize that a failed fuel injector is a probable cause of the engine failure and we are replacing the engine based on that. However, no matter how mild the modification is, GM does not endorse aftermarket calibrations in your ECM. The technician is returning your ECM to stock calibration and if you wish to continue warranty coverage, you cannot install an aftermarket calibration again.

In my opinion, doing something like this is fair, gracious and a good way to keep the customer base satisfied.

Those were the days. GM’s financial circumstances, however, have changed considerably in just one year and they have apparently affected its outlook on its warranty policy. Today, we are dealing with a company that is desperately trying to plug any leaks in its balance sheets. No upper management team wants to have countless dollars of what they have come to view as avoidable engine repairs on its books: regardless of whether replacing an engine appears fair or not. Same engine, same damage but GM has found a way to deny coverage for those of us who are caught using aftermarket powertunes.

A holed piston from a Duramax engine with a clear-cut overpower failure. Note the unusual flame pattern on the top of the piston.