Would a dirty air filter trigger a check engine light "Check Emission System". It is intermittent and seems to come on while driving on the highway when the ambient temp is below 0 C. Any ideas or suggestions? I have already checked the standard places I.E: gas cap etc and so on. Slowly going nuts with car. 2012 Honda Civic LX approx 200.000kms
No, a dirty air filter will not trigger "Check Emission System." At cruising speed, a much more likely problem is the EGR valve or port, spark plugs, or the PCV valve or its port. You might also check vacuum lines and intake manifold gasket for air leaks.
At cruising, your engine is running relatively lean and hot. Anything that could be causing it to run even leaner, or hotter, could trigger such a warning. Possible factors include poor compression (dirty piston rings, scored cylinders, dirty or worn valves), dirty fuel injectors, dirty cooling system, dirty and partially clogged catalytic converter. Codes can be misleading, so you have to troubleshoot step-by-step until you've eliminated all possibilities.
I've had several cars over the decades with this phenomenon. Hang in there, and be patient.
In fact, an extremely dirty engine air filter can cause your Honda check engine light to come. I have seen it happened many times. Engine runs and idles rough and check engine light comes on.
If you have a Honda with check engine light on, this guide is a great starting point.