This bulletin applies to 2006 and prior Hummer H2 and H3 vehicles, as well as 2006 and prior GM passenger cars and light duty trucks. GM Engineering, in an effort to determine the root cause of catalytic converter damage, has determined that aftermarket alarm systems incorrectly installed in vehicles have the potential to cause misfire codes and damage to the converter.
These alarm systems utilize mechanical relays and normal vehicle movement can trigger these relays to engage and disengage the ignition circuit while the vehicle is in motion. These disruptions of the ignition circuit, which occur in milliseconds, may cause more fuel to be commanded. Over time, this dumping of fuel on and off again can cause misfire codes and ultimately damage the converter assembly.
GM engineering could not identify any alarms that utilize solid state circuitry that would eliminate this concern. It has been determined that all alarm systems must be routed through the starter circuit in order to avoid this condition.