After replacing one of my front O2 sensors (next to the firewall) a week ago, I had my computer reset. Not long afterwards the "Check Engine" light came back on. I just had Auto Zone check the computer and it came up with the P0401 code, which they say is an EGR flow problem.

Anyone have suggestions on where I go from here?

 

Obviously you should take the EGR valve off & clean it.
Inspect the vacuum hoses.
Inspect the electrical connectors.

 

what he said

especially the first 1.

and may i ask y did u replace the 02 when its a 401

 

I had the EGR off before and it was free of obstructions and the valve motion was unhindered.

Yes, the P0401 code was listed also, but since I replaced the "O2", my milage has taken an 8-10 MPG jump and the exhaust no longer has the bad odor it had.

 

Well, I just got finished breaking down the EGR assembly.

I checked the valve motion - Worked
I sprayed the EGR body, valve, and sensor pickup with carb cleaner and it would flow through the valve when I applied vacuum to the valve (since I don't have a vise, I couldn't remove the sensor.)

When I re-assembled the unit and re-installed it on the car, I checked the vacuum:

EGR Valve - No Vacuum @ 4500 rpm
EGR - Vacuum Modulator (P) - 500mm Hg (20 inch Hg) @ 3500 rpm
(Q) - No needle movement @ 4500 rpm
(R) - 500mm Hg (20 inch HG) @ 4500 rpm
(Q - feeds Vacuum Switching Valve (which feeds EGR), P - fed by "E" on throttle body, R- fed by "R" on throttle body)

Anyone know about the port on the base of the Vacuum Modulator (connects to the main EGR flow path)?

 

After thinking about it, I think the port on the bottom of the EGR - Vacuum Modulator must be some sort of temperature control to keep the EGR - Vacuum Modulator from opening the EGR valve before the engine reaches operation temperature. I'm planning on checking this theory the first chance I get (could be why I'm not getting any vacuum at the "Q" port when I reach 4500 rpm's.)

 

grr at emision codes. im not very knoledge yet on them. good luck to ya. except 446.

 

Well, that didn't make any difference (bringing the engine to operation temperatures.)

I have also realized that 4500 rpm's is almost never realized during normal operations. While driving around over the weekend, I noticed that I run between 2500 & 2750 rpm's.

Does anyone know how the vacumm system works inside the throttlebody?

 

The ports are nothing more than holes located a little bit behind each other.

The throttle plate passes them as it opens, when one is uncovered it get's subjected to lots of vacuum, or little vacuum for some of the RPM range.

 

Maybe it's time to remove the rubber hose and check the unit for cleanliness.

 

see you should read your bible more

"cleanliness is next to holiness"

lol sorry i couldnt resist. since i strayed from my religious background i still get the urge to quote sometimes.



btw would a 150k mile vehicle benefit from changing the EGR? and does anyone have an image of where it is located?

 

Assuming yours is the same place as mine, it should be the device that is bolted onto the intake manifold just after the throttlebody. It will have a single vacumm line going to it from the vacumm switch. The EGR - Vacuum Modulator is also bolted to the assembly. The EGR is round (mine's marked 25620-2001) and the assembly is attached with three 10mm nuts along with two 10mm nuts attaching the exhaust feed tube.

 

Well, I didn't know about http://us.lexusownersclub.com/ and after discovering it today, I found this information:

P0401 "egr insufficient flow" can indicate many things, including:

1-vacuum line plugged or leaking
2-pipe from exhaust to egr valve plugged
3-pipe to vacuum modulator valve from egr valve plugged
4-passages at egr are plugged
5-bad egr valve
6-bad EGR VACUUM MODULATOR VALVE

So, off to check the items on the list I haven't looked at yet.

 

I ran across an interesting bit of information/knowledge this afternoon!

After I had replaced the front pipe of the exhaust system on the '87 Celica GT convertable, I decided to do a thorough check under the hood for broken or damaged parts for replacement. While I was standing there looking at the engine compartment, I browsed across the top of the engine and jerked back when I realized that the EGR - Vacumm Modulator was an exact replica of the one on the '95 Lexus ES300. I have swapped the units and reset the computer to see if the code P0401 completely goes away.

If the "Check Engine" light stays out, I'm planning on seeing what price Toyota wants for the Celica version. The part for the Lexus from the Toyota dealer was being listed around $65.

I'd check the Lexus unit in the Celica, but I've got a dead battery and a short which keeps blowing the 15 amp EFI fuse when the starter gets turned over. If I can get the problem resolved (which I'm sure I will) I'll see if the Celica develops a code.

If the light comes back, then it's on to another area to solve the problem.

 

That didn't work. I'll try to test the Vacuum modulator on the Celica the first chance I get.

Looks like the next step will to check the exhaust feed tube for blockage. Anyone know the best way to go about this?