Exhaust Rattle or Buzz at Engine Start - keywords 4.4 actuator LC3 leak noise

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Exhaust rattle or buzz at engine start. This condition may last up to 20 seconds after start up, usually after the vehicle has set at least over night or longer.

This condition is driven by the amount of available stored vacuum which is used to close the exhaust flow control valves located in the inner two tail pipes. When the amount of stored vacuum is low, there is insufficient force hold the valves tightly closed against the exhaust pulses. Due to the length of the vacuum supply pipes and cold start engine vacuum characteristics, it may take a few seconds to build enough vacuum to hold the valves closed firmly enough to prevent the noise.

Note: After the engine is shut down and the BCM goes to the sleep mode, the system releases the vacuum to the vacuum motors which opens the valves to allow ventilation of the exhaust system. The system commands the valves closed at BCM wake up to minimize exhaust noise at engine start. Actions like opening the vehicle's doors and or deck lid will cause the system to close the valves. If this happens a couple times without engine start, this can also cause the available vacuum to be low, leading to the brief rattle noise at engine start.

This is considered to be a normal condition and no repairs should be attempted if the condition is only experienced under the above conditions.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.