I have a 98 Camry LE with the 2.2 liter automatic that I am having a terrible time solving the problems associated with a CEL (check engine light). It is caused by a P0401 diagnostics code which has been to two different independent garages to troubleshoot and fix. Now the light and code first surfaced a year ago and I took it to Autozone and they put the computer to it and gave me the code (P0401 - exhaust gas recirculation failure?) and told me to replace the EGR which I did. This solved the problem long enough to get it passed through the emissions testing station but shortly thereafter, the CEL came back on. Because the car ran fine and with the advise of a mechanic, I choose to live with the CEL for the next year but now the time has come to sell the car and I can't seem to get anyone who knows what to do or try next. I don't want to sell it as is unless I have to. In addition to changing the EGR a year ago, I have also had the cannister purge solenoid, and EGR modulator replaced as well as had the throttle body thoroughly roded out and cleaned twice. All vacuum hoses have been checked and as far as I know, all diagnostics possible on the system have been checked and are working fine. And as I said before, the car runs perfectly and only has 143,000 miles on it. I haven't replaced the PVC valve but surely one of these genious mechanics I've had working on it would have checked that would they not? I mean what are they, 5 dollars?

Every time I have had it worked on and had the code mechanically cleared, it comes back on after about a 20 mile driving cycle. Any help or suggestions would be greatly appreciated. Thanks so much.

 

"A code P0401 most likely means one or more of the following has happened:

The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
There is a blockage in the EGR (tube), most likely carbon buildup
The EGR valve is faulty
The EGR valve may not be opening due to a lack of vaccuum"

First I'd do since you replaced the EGR is check and clean the EGR tube. If you have been burning oil then the EGR may be blocked again and can be cleaned.

 

Thanks Pedro but all of that has been done and checked and it is not burning oil at all. All tubes and lines are clear of carbon.

 

Even the DPFE sensor?

 

As far as I can tell and based on my research and what I've been told from these two mechanics who have worked on it, there are no other components to the system. In other words, it doesn't have a DPFE. I just searched for that part on auto part sites online for a 2.2 liter 98 camry and can't find it anywhere. Is it known by any other name. I have replaced VSV, EGR, and EGR modulator. Perhaps the modulator is what you are referring to? It has one vacuum tube on the bottom and then 3 more on the top. It is shaped like a disk.

 

There has to be a sensor somewhere telling the ECM of low EGR flow, unless it's a position sensor for the opening of the EGR.

 

Yeah Pedro gotcha, it is called the vsv (vacuum switching valve) and it did test faulty and was replaced with a brand new one. Surprisingly, this didn't do the trick. No one has mentioned it to me but could faulty plug wires or fowled plugs cause the P0401 code? 144,000 miles and it is the original wires.

 

My understanding is the VSV controls the opening/closing of the EGR. It is electrically operated by the ECM to open/close the EGR at the correct times and duration. It is NOT a feedback sensor that tells the ECM when there is too little EGR flow. My manual only goes to 1996 and talks about an EGR gas temperature sensor - it appears to be the feedback to the ECM that may trigger the code. I don't think you've found the sensor yet that the ECM uses to establish the code. Search the manuals for your year. Certainly any bad connection can trigger a code.

 

The problem lies in the EGR VSV. It is mounted in a difficult to reach location above the passenger side CV axle on the block. EGR flow is verified by using the map sensor to detect a drop in manifold vacuum when EGR is activated.

JJ