GM has taken a fairly agressive stance on engine modifications:
DocumentID: 2365177 #09-06-04-026A: Identifying Non-GM (Aftermarket) Engine and Transmission Calibrations for V8 Gas
Engines – (Oct 28, 2009)
General Motors is identifying an increasing number of engine, transmission and catalytic converter part failures that are the result of non-GM (aftermarket) engine and transmission control calibrations being used.
When alteration to the GM-released engine or transmission control calibrations occurs, it subjects powertrain and driveline components (engine, transmission, transfer case, driveshaft and rear axle) to stresses that were not tested by General Motors. It is because of these unknown stresses, and the potential to alter reliability, durability and emissions performance, that GM has adopted a policy to cancel any remaining warranty coverage to the powertrain and driveline components whenever the presence of a non-GM (aftermarket) calibration is confirmed – even if the non-GM control module calibration is subsequently removed.
Warranty coverage is based on the equipment and calibrations that were released on the vehicle at time of sale, or subsequently updated by GM. That’s because GM testing and validation matches the calibration to a host of criteria that is essential to assure reliability, durability and emissions performance over the life of the warranty coverage and beyond. Stresses resulting
from calibrations different from those tested and released by GM can damage or weaken components, leading to poor performance and or shortened life.
Additionally, non-GM (aftermarket) issued engine control modifications often do not meet the same emissions performance standards as GM issued calibrations. Dependinq on state statutes, individuals who install engine control module calibrations that put the vehicle outside the parameters of emissions certification standards may be subject to fines and/or penalties.
This bulletin outlines a procedure to identify the presence of non-GM (aftermarket) calibrations. GM recommends performing this check whenever a hard part failure is seen on internal engine or transmission components, or before an engine assembly or transmission assembly is being replaced under warranty. It is also recommended that the engine calibration verification procedure be performed whenever diagnostics indicate that catalytic converter replacement is indicated.
In May 2009, the PQCwill begin piloting a process to confirm the ECM/PCM calibration is GM issued. Beginning on May 18, 2009, the PQC will require a picture of the engine calibration verification screen, as outlined in this bulletin, before authorizing any V8 gas powered engine replacement.
If a non-GM calibration is found and verification has taken place through GM, the remaining powertrain and driveline warranty will be cancelled and notated in GMVIS and the dealership will be notified.
The Magnuson–Moss Warranty Act gives US buyers certain protections with regard to warranties. In order to flatly deny warranty coverage, GM must prove that the Consumer has done something to cause the problem. It is not clear to me that GM is correct to argue that because they don’t know if an aftermarket calibration might have caused the problem, they then can deny coverage. That does not seem to be in keeping with the Magnuson-Moss Warranty case law.
I am all for everyone taking responsibility for their actions. If you get an aftermarket tune that takes the engine lean and end up blowing the engine, then that’s on you and not a warranty covered item. On the other hand, if you happen to have an aftermarket tune and the engine fails due to an unrelated defect, that should continue to be covered under the powertrain warranty. I understand GM’s argument that if you have an aftermarket tune, there is no way to determine if it was a causal factor or not. But I don’t think that is a strong enough argument — it does not constitute proof that the user installed modification caused the problem, which is the requirement.
I think the right thing to do here is to document that if the failure can be clearly established as a result of the aftermarket tune and not as a result of an unrelated failure, then warranty coverage would be denied.