When changing the air filter, it is easy to knock off a hose on the air filter housing, which is part of the emission control system. If the vehicle is driven with this hose disconnected, the Check Engine Light will illuminate.Google+
Car Problem Reports
Lexus ES300 Check Engine Light Due to Hose Off of Air Filter Housing
Lexus ES300 Problem
Engine Affected: 3.0L V6
Visitor, 2002 Lexus ES300, 3.0L V6, 208,000 mi
I took my car to the dealer for an oil and filter change. Within a few days, my check engine light came on, and I took it to the place who did the prior smog check. They lifted the hood and showed me that the nub where a hose connects to the front of the air filter housing was broken off in the hose; the hose was disconnected. I took the car back to the dealer, who epoxied the nub back onto the housing. This repair lasted a few days, and I noticed the hose was again off and the nub was in it. The dealer ordered a new air filter housing, and I am waiting for it to come in to be installed.