Knock Knock….It’s Your GM Engine Knocking

June 7, 2012
By: Robert Silverman

It’s a problem we have seen for over a decade– a piston slap and engine knock on cold start with various General Motors vehicles. Now, the latest technical service bulletin is out and it includes 2012 models as well.  Here’s a copy of the TSB courtesy of our friends at pistonslap.com (website no longer available, links removed).

The most current models affected are 2007-2012 Cadillac Escalade, 2007-2012 Chevrolet Silverado, 2207-2012 GMC Sierra, 2007-2012, GMC Yukon Denali, and the 2007-2012 GMC Yukon XL Denali equipped with the 6.2 liter engine.

According to the TSB, the noise may begin in the first 12,000 to 15,000 miles and lasts between 5-30 seconds.  The noise is more noticeable when the weather is below 50 degrees.  The engine knock may be caused by an interaction between carbon that has formed on the piston, the piston motion, and the cylinder wall.  GM engineering feels that this engine knock or piston slap is not detrimental to the vehicle.  We are not so sure of that.

If you have been repeatedly for your General Motors engine knocking, it is essential that you look into your rights under State Lemon Laws and Federal Warranty Laws.   You could be looking at recourse and the help is free.  Contact a Lemon law Lawyer in your state for more information.