Check Engine Light - P0401

I live in one of the four counties in Utah where Emissions Testing is a requirement for vehicle registration.  Recently, my 98 Toyota Rav4's check engine light came on.  Ugh!  I went to Autozone for a free diagnostic.  Thirty minutes later, they must have forgotten about me!  I went down the street to O'Reilly Auto Parts for a free diagnostic, and they let me borrow the tool to test it myself.  They even showed me how!  It ended up being error code P0401 which is "Insufficient EGR Flow."  Note: Autozone online has high quality parts for cheap, but I am boycotting their local stores.  O'Reilly Auto Parts has always been good to me, even recommending other places if they don't have a part.

The problem:  Error Code P0401 means your car won't pass emissions.  I did a lot of research about Toyota's with this error code and found that you should not take it to a mechanic.  They will end up changing the wrong part, reset your diagnostics, and charge you for an hour's worth of labor (even if it only took them 10 minutes).  A few days later your check engine light will come back.  You're probably thinking to yourself:  Why not just disconnect the battery or reset the diagnostic to remove the check engine light and then take it to get tested?  That doesn't work.  Your vehicle has to complete a "drive cycle" before you get it tested.  That means you have to drive it 20-50 miles.  Believe me...I've tried this method.

I admit it, it was near the last day of the month and I procrastinated getting my vehicle inspected.  I drove around for awhile hoping the Check Engine Light would go away, but it never did.  I ended up going to Jiffy Lube (which I don't recommend doing).  I failed both Safety and Emissions.  The good thing about failing is that you get 15 days to fix the problems, so you can't get ticketed.  I failed Safety because my turn signal lens had a crack in it.  This must have been a recent occurrence.  They also said my passenger headlight was out of aim.  I checked and it didn't seem that far off.  I am boycotting Jiffy Lube as well now.  Not just because they won't step off their high horse about the headlight, but because an oil change shouldn't cost over $30.  You can buy oil, and a filter for $17.99 at O'Reilly Auto Parts.

The plan:  There are four possible reasons as to why I received a P0401 error.  1) The EGR Valve is corroded.  This usually isn't the reason.  A new EGR Valve costs $143.  2) The EGR Vacuum Modulator has little to no suction.  This is usually the problem.  A new EGR Vacuum Modulator costs $54.  3)  The EGR Vacuum Solenoid is bad.  Not usually the problem.  This costs $88.  4) The EGR port is clogged.  (small wire brush and some cleaner will do).

Usually, just buying a new Vacuum Modulator ($54) and completing a drive cycle will fix the problem.  Since I have no plans of selling this vehicle, as Toyota's can get over 300k miles with ease, I decided to just buy all new parts.

Update: Two years later...it was finally fixed. See the update.