A recent GM bulletin and e-mail question from a reader has helped bring the issue of aftermarket parts and their impact on warranty claims to the forefront.

The bulletin was #07-00-89-043, and addressed the issue of modified vehicle programming.  The bulletin states that, "General Motors will void the warranty coverage for those components that are damaged or otherwise affected by the installation of the non-GM part and/or control module calibration."  The trick is whether or not you can determine cause and effect - did this alteration cause this damage?  Our e-mail question came from a service manager looking for advice in handling both GM and a customer in light of the discovery of an exhaust brake on his diesel engine.

Aftermarket accessories are not just confined to alarms, keyless entry and remote starters anymore.  We now have widespread use of appearance and performance packages, entertainment centers with DVD players and satellite radios.  So what happens when a customer comes in with a problem that might be related to an aftermarket accessory?  How do you handle these repairs with respect to GM's warranty?  The easy answer is to play it safe and deny any warranty coverage.

But not so fast - a customer that realizes their rights under the Magnuson-Moss Warranty Act would not be so easily swayed.  We have an obligation to provide warranty service on GM's behalf and that includes analyzing the true cause of the complaint.  And, as a not so small side issue, we'd like to take care of the customer.  These situations put you squarely between the interests of the customer and those of GM.

Magnuson-Moss in a long-winded way says that no manufacturer can make it a condition of its warranty that customers only use a certain brand of parts, products, or services.  However, the Act does allow manufacturers to deny warranty coverage if the aftermarket part causes the damage or problem. 

For GM's part, its Policies and Procedures manual Article 1.2, page 13 is a little softer as it says, "Damage, failure, or reduced life of the engine, transmission emission system, drivetrain or other vehicle components caused by aftermarket engine performance enhancement products or modifications may not be covered under the vehicle warranty or GMPP plan."

Getting back to our example, let's assume that the engine's turbocharger had failed on the truck equipped with the exhaust brake.  Rightly so, the service manager suspected that the brake had contributed to the failure.  But he, and you, should tread lightly.  Be careful not to suggest that you know conclusively what the problem is or even that you are looking to prove that the engine brake is the cause of the problem.  Have an objective and professional discussion with the customer and indicate there is a possibility that the brake is causing the problem.

Not only do we not want to bias the customer or technician to our suspicions, we also don't want to suggest in writing something to GM that may not be true.  As soon as you introduce a variable to the repair that might suggest a cause other than warrantable defect, you are putting the claim at risk if reviewed in the future.

Gather as much information as possible.  Useful evidence could be a photo of the damage, history (e.g., problem didn't occur until after the part's installation), and any related service bulletins.  Once you have the proof you need, you should provide the customer, with as much definitive proof as you have, why you are denying warranty coverage.  You need to describe the failure and exactly how the aftermarket part or installation caused the failure.  Then I would suggest that you pass this information on to your GM rep or by calling the DBC.

Just make sure that the proof is on your side and that you've got a well documented repair on your hands.  And when in doubt - punt.  Gather all the information and then kick it over to your rep to make a decision.