P1491 and P0401 Error Codes in Honda Odyssey After Air Filter Cover Fastener Damage?
I recently started seeing frequent P1491 and occasional P0401 error codes on my 2015 Honda Odyssey after a local quick lube service. During that visit, the air filter was replaced, and I believe one of the four fasteners securing the top cover of the air filter compartment was broken off. The cover is currently tight with three remaining fasteners, but I'm concerned whether this could allow unfiltered air to enter through the gap, potentially affecting engine vacuum or EGR performance. The P1491 code (Evaporative Emission System Leak Detected) appears frequently—about 10 times in the past week—with only one instance of P0401 (EGR Flow Malfunction). My engine has 140,000 miles and was last serviced at 130,000 miles with an intake cleaning, new timing belt, water pump, and other components. I'm not a mechanic, but I'd like to understand if the air filter cover issue could be contributing to these error codes. Since the leak is located above the MAF sensor (before the mass airflow measurement), unfiltered air would still be measured by the MAF—so it's unlikely to directly cause EGR-related issues. However, a vacuum loss in the intake system might indirectly affect EGR operation or emission control performance. I'm seeking clarity on whether this cover leak could trigger P1491 or if another component (like an EGR valve issue) is more likely responsible.
A broken fastener on the air filter housing may allow unfiltered air to enter, but it won't directly cause an EGR-related error code. The leak occurs before the MAF sensor, so whether air is filtered or not, the MAF measures total airflow. Therefore, a leak in this area doesn't impact EGR flow measurement. However, EGR systems on older Honda Odysseys have known high failure rates due to carbon buildup and port clogging—this may be a more likely root cause.