Hyundai Repair: problem error code p0401, hyundai santa fe 2004, egr solenoid, hyundai santa fe

Question
hello,
my car has problem, error code p0401  Any help and soluctions would be very much appreciated.
Thank You

Answer
Hi, Manuel.  This trouble code indicates a problem with the EGR system's performance.  Unfortunately, it doesn't give much help in determining the specific cause of the EGR problems.

Here's how the EGR system in your vehicle works.  

The green striped hose coming from the throttle body has vacuum in it.  The hose is plumbed to a tee.   From the tee, one green hose goes to the EGR valve itself and another goes the the EGR solenoid.  A yellow hose then goes from the EGR solenoid back the the throttle body.

Under normal conditions, the EGR solenoid is open, allowing the vacuum to vent back to the throttle body.  When EGR operation is desired, the ECM actuates the EGR solenoid, closing it, causing vacuum to be applied to the EGR valve.  If working properly, the EGR valve should then open and allow exhaust gases to recirculate.

Here's how I typically test the system.  With the engine running, I first pinch the yellow-striped hose shut at the throttle body.  This mimics the ECM commanding the EGR solenoid closed.  If the engine begins to stumble and run poorly, you've just verified that all the hoses are connected, the EGR valve opens properly, and that the passages are clear.  In this case, you're left with only two components that could be the issue-- the EGR solenoid and the vacuum bleed off valve (called a vacuum switch by Hyundai).

If you arrive at this point, I typically recommend replacing both components.  The solenoid has a habit of failing intermittently, making a good diagnostic test result questionable, and the vacuum bleed-off valve is difficult to test-- in fact, I've never seen anywhere a test procedure for the valve.

I'd left the vacuum bleed-off valve out of the description of operation above because it would most likely make things unnecessarily complicated.  It's purpose is to prevent EGR vacuum from becoming excessive, while still allowing an appropriate amount to reach the EGR valve.  If my memory is correct, it's in-line in the green striped hose between the throttle body and the tee.