allright, few weeks ago I tried getting some help from here on a check engline light with code 0401. (2000 prelude)

well, simple test. ODBII will specifiy if a sensor that the EGR reads from is bad, so that is easily ruled out. Run a voltage and vacuum test on your hoses and EGR, test it to make sure it holds etc. If that tests out fine, your problem is this:

it took $240 for a mechanic to fix mine. Carbon buildup in the fuel injectors and in the exhaust port.

if anyone knows a treatment or method to keep carbon buildup low or kill it before it gets bad enough to decrease gas milage severely, please post it here, it could avoid expensive problems in the long run.

hope this helps someone, I only found 2 people archived that had this same problem and never a solution to their problem...

-sam