One of the most common codes I typically see on a 1997-2001 Toyota 2.2L Camry 4Cyl is a P0401. It is a code that indicates there is a problem with the EGR system, not necessarily a problem with the EGR valve itself. I hear stories of people getting this code and replacing the EGR valve without doing any testing because they don’t know what to test. They spend unnecessary money and still haven’t fixed the problem.
There are three parts that will generally cause this code to appear on your car. Yes, the EGR valve is one of them, but you also have the EGR VSV and the EGR modulator. The first parts of the inspection will be to check the operation of the EGR valve by applying vacuum with a vacuum pump. You can get a vacuum pump at an auto parts store for around $20, and even rent one from some stores.
Connect the pump to the only vacuum port on your EGR valve. There will be a small hose attached, which you will need to disconnect and install your pump into the same port. With the engine idling, you should be able to pump the vacuum pump to create a vacuum at the EGR valve. The diaphragm inside the EGR valve should rise and cause the car to die. If your car dies, then your EGR valve and ports are fine. If your car stumbles or doesn’t have any change in the way it runs when you’re vacuuming, you probably have a bad EGR valve or a clogged port on your intake.
If you think you have a bad valve, you should remove it from the engine and test it with the same vacuum pump. You should be able to see the diaphragm move inside the valve as you apply vacuum. If the diaphragm moves, you may have clogged ports in the intake and the intake may need to be cleaned. If it doesn’t move, you need to replace the EGR valve.
However, if your Camry stopped working when you applied that first vacuum, then you need to start looking for the EGR VSV. I know VS what? It’s a small blue solenoid located on the back of the engine block. It will have a couple of vacuum hoses and a small plug attached, all held in there with a 10mm bolt. Remove the VSV and test it by applying power and ground from your car battery (VSV should not be connected to the harness during testing). If you hear a click in the VSV when you apply power, then the EGR Modulator needs to be replaced.
The EGR modulator is located to the right of the EGR valve above the intake. It will have several vacuum hoses coming out and it slides into a bracket. The EGR modulator can be purchased relatively cheaply from your dealer. There are no easy tests for the modulator. If you replace the modulator and still have a problem and the light comes back on, you need to replace the EGR VSV, also known as a vacuum switching valve. Sometimes the VSV can have an internal break and still click when you power up and ground the terminals, but it can still be damaged.
So you could be wasting your money just throwing a valve. Remember that the only way to fix something right is to know the proper testing procedure so that you can arrive at a correct solution.