I have a 99 Honda Odyssey with a code P1491 and a code P1491 Pd. They are the same code but one says Pd after and I don't know what that means. The code means EGR Valve insufficent. I'm guessing that the EGR valve needs replaced. If it is something else please let me know. The car seems to have to no mechanical problems beside the transmission shifting a little rough at times. Also where is the EGR valve located on this vehicle? The other problem I'm having with the van is that the traction control light comes on periocically and stays on until the car is turned off. When the light is on the transmission sometimes shifts rough. The RPMs go up to around 4000 RPMs and then it shifts roughly into the next gear. If anyone can help me out with these problems that would be great. If you need any more details just ask.

 

Sounds like you need to perform the EGR Technical Service Bulletin. Replace the EGR valve, ream the port of carbon, insert teflon sleeve and clean intake.