I get an intermittant engine code (about once a week but sometimes more often) that is P0401 - EGR Low Flow. The first think I did was to warm up the engine, then with a finger touching the EGR diaphram, I would increase RPMs to about 2000 rpms. I'd notice the valve would open but within a few seconds it would shut and stay shut until I let off the throttle. This was repeatable every time I tried it with the EGR valve opening each time for a few seconds then closing while I was still holding the throttle at high rpms (about 2000 rpms). I figured I'd just replace the EGR valve and gaskets, the vacuum hoses, the modulator thing next to the EGR valve and the VSV valve and I cleaned out the vacuum fittings into the manifold using pipe cleaners going pretty far in. That should do it right? Wrong - I still have the same problem. I've checked the following - If I manually open the EGR valve with a vacuum pump, the engine stalls immediately. If I put my finger over the EGR vacuum hose and increase rpms, I can feel the suction then it cuts off after that few seconds and stays off until I cycle the RPM's again. I have also tested for exhaust blockage by watching the vacuum to see if it drops at high rpms - it stays high. Also, there is no vacuum to the EGR at all when the engine is cold. I also bypassed the VSV valve and when I do that, the EGR system works and keeps working. Something is shutting off the vacuum supply by applying power to the VSV valve (incorrectly). I've read that the MAP sensor can fool the system and trigger this error but I am tiring of just replacing parts. Has anyone experienced this and solved it - or does anyone have some suggestions? If someone helps me solve this, I will pay for the help. I am good with meters and electronics. This problem started suddenly about a month after replacing the front O2 sensor. At that time, I was getting an O2 heater failure and that went away when the 02 sensor was changed. The parts used have been all geniune Toyota parts brand new. I am not getting any other MIL codes. My scanner can't do live monitoring that I know of but I do know how to use an ohm meter. Any help is appreciated. This is a Japan made 4 cylinder version with 70k original miles on it. It runs great except for this problem. Please help if you can - I'm out of ideas. Respectfully, Dennis
P0401 after new EGR valve, modulator and VSV valve - what else? on 1999 Toyota Camry
by 1californiadreamer in National City, CA on May 30, 2010
3 answers 1 comment
ANSWER by Bret Bodas , May 31, 2010
Dennis, We have some really good info about the P0401 code for your Toyota written by a technician who deals with these problems everyday for the state of California, see it here: http://repairpal.com/OBD-II-Code-P0401-Toyota
ANSWER by brent85224 , March 06, 2013
Check your thermostat. If your engine is running cool (thermostat stuck open) your egr will not kick in. So your egr is not running as much as its supposed to and you get inefficient egr flow. Check thermostat get on highway go 70 for a decent length it's your temp gauge showing below what it should be at?
ANSWER by Visitor , June 29, 2010
On air filter case near the mass airflow sensor you will find a small ( 1/2" ) hose running down to a couple of evap system components. Make sure this is connected. Mine was off and I had the same P0401 code with all my EGR components checking good. My guess is that when this hose is off it throws off the MAP sensor readings.
COMMENT by 1californiadreamer , June 29, 2010
My car doesn't have a Mass Air Flow Sensor - instead it measures the intake manifold pressure directly using something called a MAP sensor that is mounted to the firewall. Thanks for trying. For those interested - I think I solved this problem. If you've ever changed a VSV valve, you khow how hard it is to get to it. Because of that, I moved mine and when I did that, I never got the error again (and this was a new VSV valve I had been still getting the error with. Don't know if I loosened something in one of the vacuum hoses or if it just likes the new position better - but so far it's been 3 weeks and no engine light. I didn't cut or replace anything - just moved it to place where I could reach it easier if I needed to work on it again. (moved the the left directly under where the hoses come down from the top to it.