I was pulling my trailer to Moab, UT today and the check engine light came on. Pulled code, came up 404. What would cause this code to be set?
Thanks

A Dirty EGR or clogged intake manifold can...

Code: P0404
Description: Exhaust Gas Recirculation Circ Range/Perf

What should I do next?

i forget, do you have efi? and is the egr blocked?

No, I don't have either.

Correction, it was code P0401 instead. It only sets when I am towing under load and on the throttle somewhat. It never comes on with regular driving with out the trailer. Should I worry about this, is it going to cause problems?

Correction, it was code P0401 instead. It only sets when I am towing under load and on the throttle somewhat. It never comes on with regular driving with out the trailer. Should I worry about this, is it going to cause problems?
Insufficient EGR Flow p0401 code

Technical Description

Insufficient EGR Flow
What does that mean?

EGR stands for Exhaust Gas (http://www.obd-codes.com/p0401#) Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve (http://www.obd-codes.com/p0401#), an actuator solenoid, and a differential pressure


You may notice drivability problems such as pinging (a.k.a. pre-ignition knock) when the engine is under load or the vehicle is at higher speeds. There may also be other symptoms.
Causes

http://konac.kontera.com/javascript/lib/imgs/grey_loader.gif
(http://www.obd-codes.com/p0401#)sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation based on engine (http://www.obd-codes.com/p0401#) temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR.
http://www.obd-codes.com/images/copyscape.gif
Symptoms