Owners of General Motors Duramax diesel-powered trucks who have modified their vehicles with aftermarket engine performance parts or computer tunes that increase horsepower may find that such modifications will void the factory powertrain warranty. GM says it will NOT honor warranty claims for any engine, transmission or driveline hard part failures, or exhaust particulate filter or diesel oxidation catalyst failures if a vehicle has been modified with an non-GM PCM calibration (performance tune) or other power-boosting aftermarket components.
If you are considering reprogramming your PCM for more power or making other modifications to the turbo, engine or exhaust system, perhaps you should think twice BEFORE making such modifications. GM says if anything breaks, so sad too bad -- even if you have removed such modifications and returned the vehicle to stock after having made any of these changes.
GM Service Bulletin 08-06-04-0061 issued February 16, 2012 covers the following trucks:
2006 to 2012 Chevrolet Express, Kodiak and Silverado
2006 to 2012 GMC Savana, Sierra and Topkick
With any of the following Duramax diesel engines: LBZ, LGH, LLY, LML or LMM
GM says it cannot warranty any component failures that result from aftermarket modifications because such modifications subjet the engine, transmission, driveline and exhaust components to to stresses they were not tested to handle. So if you modify the power output of your Duramax diesel, you do so at your own risk.
The Duramax diesel engine warranty bulletin tells technicians to hook up a scan tool to the vehicle and to examine the calibration history of the engine computer. If the calibration is non-stock, or there is evidence that it has been modified in the past, they will document the evidence and use that information to essentially void your warranty.
In all fairness to the makers of performance tuner scan tools for the Duramax, most of the PCM tunes have been dyno proven to be relatively safe at moderate boost levels. Increasing the boost pressure generated by the turbocharger makes more horsepower. A Duramax engine should be able to safely handle an extra 50 to 100 extra horsepower without any problems. Higher boost levels that increase horsepower 150 or more will increase the stress on the engine, which increases the risk of something failing.
A lot also depends on how you use the extra horsepower. If you're smoking the tires, driving your truck in a truck pull or otherwise abusing it and pushing it to the max, the risk of failure goes up. The risk of the transmission failing or something in the driveline breaking goes up with the power output of the engine. Also, the stock diesel particulate filter and catalytic converter may not handle the extra heat in the exhaust that can result from a highly modified engine. And if they do break, don't ask GM to pay for the repairs. You made the mods so you are stuck with the consequences if anything does break.
Here is the first page of the GM diesel warranty bulletin: