Within the past couple of months, I have been receiving "check Engine" light. A code scan showed me P0401, EGR, problem with the car. I took off the EGR Volve and Module, not at the same time, and did a thorough cleaning. I also clear the code from the system. The warning light came back after about a week. I replaced both part, not at the same time, the light came back again in a week, but went away in a few days after that. Since then, it has been going on and off. each time it will be for days before it switches to the other way. The car drives fine. I don't sense any performance problem. Today I went to a local STS. They told me to check for computer reflash. I am not sure if that is a best way to go at this point. I was also told about a thermo switch/sensor to check on. Can anyway tell me where I can find the sensor? or at all, any other approach I can take on finding the problem.

 

What is "STS?"

What engine V6 or 4 cylinder?

 

Sorry, STS is http://www.ststire.com/

it is V-4.

 

Computer reflash?

You might check with a Toyota dealer and find out if there are any applicable technical service bulletins for this year/engine type car about this trouble code.

If the EGR system has a gas temp sensor it would be mounted on the EGR valve. The sensor would be connected to the cars computer via wiring.

The temp sensor seldom fails.

More common is the electric valve (VSV) that controls vacuum (turns on or off) to the EGR valve. The valve responds to changes in vacuum (opens/closes) on the diaphragm on top of the valve.

The VSV valve can fail resulting in the EGR system being off all the time.

Another common issue is the EGR valve or exhaust gas tubing becomes clogged with carbon. Was the exhaust tube connected to the EGR valve clear along with the port on the cylinder head where the valve bolts to?

One test is with engine at idle, apply vacuum to the small hose going to the EGR valve. This will open the valve and allow exhaust gas into the head. If gas is flowing the engine will die or have a rough idle.

 

Well i would suggest you to get your car checked by a good mechanic.he'll be able to guide you what's wrong.

 

So I went at it again today. I removed the EGR valve, EGR modulator and three hoses and cleaned them all. the only thing I noticed was the filter inside the modulator was thick and dirty. I will have to search for a replacement. I refered to the Haynes book for more information. It mentioned about VSV for my EGR. could that be my step?

 

The VSV can go bad.

See Private Message.

 

The fact that the warning light goes in and out, makes me think that some sensor is broken. needs to perform more testings.

 

The computer measures absolute manifold pressure via the MAP sensor and compares this with what it calculates it should be with EGR valve on. If not the same, a code is tripped.

The computer needs to run the same test twice with 2 failures. The test requires that certain driving conditions be met , such as MPH when engine warm. Thus if there was a problem, it could take some time before the computer sets the light.

 

so ... after last weekend cleaning, the light has not returned. the only effective thing I did was to rotate the filter in the modulator. maybe that open up the airflow a little bit. will keep monitoring it for awhile.