How to diagnose and replace a failed EGR vacuum modulator.
Looks like P0401 is a common problem on ’92-’96 ES300.
I just fixed mine after doing some research on the forum.

All the information is out there but it’s all scattered and unclear.
I decided to put it all together in one place and throw in some pictures for DIY.

So you have P0401, which states for EGR insufficient flow.
Most likely you will find the problem by checking:
1. EGR Valve
2. EGR Vacuum Modulator
3. Vacuum hoses
It’s easy and I am going to explain how to do it. Read on below.
But if by checking things outlined above you could not find the problem,
then there aren’t many thing left to check: EGR gas temperature sensor and VSV.
But I didn’t have to do it and most likely neither will you.

So, here is what we’re looking for under the hood:

 

Checking if the EGR Valve itself is working OK.
With engine running disconnect the EGR valve hose and apply
vacuum to the port that the hose was connected to (I just leaned over
the engine and sucked on it If engine stumbles it means that the
valve is working fine.
Shut off the engine. Now we are going to check the EGR modulator.
We need to take it out first. Disconnect the vacuum hoses from it (all three).
Unscrew the bolt holding it in place. Pull it up until it comes off.

 

Now you can take the modulator out of the springs that are holding it.
Apply vacuum to the bottom port. Again, you can just use your mouth.
If it doesn’t hold vacuum – the membrane is broken and you need to
replace the unit.
As of today I paid $78 at AutoZone (special order, takes
them a couple of days to get it in store). Or you can get one from Lexus dealer
for $91 or from Toyota dealer for $92 (tell them you have the same year Camry SE V6).
If the test shows that the unit is fine, check all the vacuum hoses, make sure they aren’t clogged. Good luck with your P0401.

 

This is what my old modulator looked like inside.

 

BTW you can reset check engine light by pulling
out the EFI fuse for 10 sec (engine off, key out for more then 90 sec). The fuse is in the main fuse box under the hood.

 

are these the same for a 98 ES?

 

Good job pon-alex!

 

Nice write up. I'm sure this will definitely help a lot of people.

 

Thank you sir

 

thanks for the writeup, alex. I just got the p0401 code a few days ago myself (along with the bank1 O2 code)

 

oh just to add, when i pulled the EGR off of my old engine, it was completely stopped up. The old engine had 200k+, so that's another thing worth checking if everything else is fine.

 

What will the car do (performance wise), if there is problem with the EGR?? Also, has anyone had one go bad without the CEL coming on?

 

Nice write up. A big for taking the time to do this.

 

Awesome write-up.
I move/request that this be added to our DIY sticky thread.

 

Thanks again pon-alex, I just replaced the vacuum modulator after testing it and the CEL seems to be gone for good.

Just for reference:
Auto Zone had it for ~$78 but they had to look it up for a Camry V6, it wouldn't show up under an ES300 at all.