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Hello, I have a 2000 Camry, 4 cyl 2.2l, 5S-FE, auto trans, 235K miles with a P0401 code. It is driving me nuts.

I read all the info I could find on the forum. The EGR modulator was filthy and the filter clogged. I replaced it. Reset ECU. The P0401 returned. Did all the tests in the factory manual. Everything OK. Replace the EGR valve, thought it might be sticking. The old valve was clean but you never know. Reset ECU. The P0401 returned. Read about the VSV failing in the heat of actual operations. Changed the VSV. Also got a low coolant pending code (I will discuss later). The P0401 returned.

The coolant temp was somewhat of a mystery. I live in central Florida so it is hot. I have a Bluetooth OBDII with Torque app. The coolant temp was in the 160's most of the time. 180's sometimes. Replaced the thermostat and it reads 190 fairly solid. Funny thing the gauge in the car looks about the same. Maybe they read from different sensors.

Other things: When doing the factory tests with the TE1 and E1 terminals connected, I can feel the EGR valve open(diaphragm lift). With the car idling, I manually open the EGR valve and the car dies. This leads me to believe that exhaust gas is flowing.

I teed a vacuum gauge into the EGR valve and went driving. The vacuum looked appropriate for when the EGR should be open. Idle - closed. Slow acceleration - open, press harder it closes. Driving along with it on, let off gas and it closes. I was using a combination vacuum and fuel pressure gauges. It read about 2.8 inches. The gauge may not be too accurate in the lower scales. The VSV reacted quickly to all the changes. To me, this means that the vacuum line are OK and the mechanics of the system are OK.

Other background. I got the car two years ago from my father. He did very little maintenance on it. It may have sat in Miami for a few months before I got it. The CEL came on during the two hour highway drive home. I drove it for two years with the CEL on. Fixed many other things and now trying this.

So now I am thinking the EGR pipe may need to be cleaned. Could it be partially obstructed and not give enough gas flow? Enough to satisfy tests but not enough in actual operations?Is it necessary to remove the pipe? I have read about a shop vac and SeaFoam.Any ideas, Could it be a MAP sensor?

Thanks!
 

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96 Camry 5-spd
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I think P0401 code is strictly related to the EGR system only.

Some members here with P0401 had tested their VSV good, but they replaced it anyway with a new one and the problem got fixed.
 

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Two of the most common failure points in the egs systems on that engine are carbon buildup between the EGR valve and intake passage, and VSV failure. Given that you have replaced the valve and it kills the engine when you apply vacuum I would say you dont have a restriction problem. The 2.8 inches of vacuum sounds way to low. MAybe the VSV is not opening fully.
 

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Discussion Starter #5
No vacumm in port R

Dear ShawnM,
I think you are correct. The 2.8 inches may be too low.

Dear Nark,
Thanks for the link. It has a diagram that explains the EGR modulator.

I hooked up a vacuum gauge to the R port of the throttle body. It is supposed to supply vacuum to the EGR modulator above a certain throttle position. The P port supplies vacuum at any position above idle. The P port is OK. The R port never supplied any vacuum. I got up to 70mph and had a steady vacuum reading in the intake manifold(with my Torque app) but no vacuum in the R port.

Here is a link:



http://personal.utulsa.edu/~nathan-buchanan/93fsm/engine/77exhaustg.pdf


From what I have learned? The P port opens the EGR to a "low" position because of the EGR modulator. Here the EGR valve cycles open and closed. Above a certain throttle position, the R port becomes active supplying vacuum to the EGR modulator. This closes something that causes full (high) vacuum to the EGR valve. It open all the way and stays open.


So now I need to diagnose how to get the R port working on the throttle body.

Any ideas?

Thanks, I think I am getting close!
 
 

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I’m just a tad late to the party. I found the the vacuum R port clogged with carbon in the throttle body. I wasn’t getting the 5 hg needed to supply vacuum to the modulator. Cleaned the TB and my P0401 never came back. Hope you got your P0401 figured out or another subscriber can use this for their troubleshooting.
 

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Sometimes the vacuum hoses have gone bad and are leaking. THat's another potential cause.

I've had the EGR error since day one of my 2000 Camry. I drove it just fine for years before I decided to do an engine swap lol.

Then again, I live in a province that doens't have emissions regulation :)
 
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