EGR Vacuum Modulator Valve on Gen. 3 Camry

[timothyl2184]

Hello,

I have a Gen. 3 Camry with 215,XXX on the clock and I'm throwing the PO401 "EGR Flow Insufficient" code. Had the EGR valve worked on but the code still comes back. I have read online that the EGR Vacuum Modulator Valve is usually the culprit, but I don't know where it is or how to remove it. Any ideas? I have a basic knowledge of cars but I just don't know where it is on the 5S-FE....thanks for any help.

[csaxon]

[csaxon]

[93celicaconv]

This might help:



You can also test this modulator to see if it funtions:

Engine Stopped:
(a) Disconnect vacuum hoses from ports P, Q, and R of the EGR vacuum modulator
(b) Block ports P and R with your finger
(c) Blow air into port Q, and check that the air passes through to the air filter side freely

Engine at 2,500 RPM:
(d) Start engine, maintain speed at 2,500 rpm
(e) Repeat the above test. Check that there is a strong resistance to air flow
(f) Reconnect the vacuum hoses to the proper locations

If operation is not as specified, replace the vacuum modulator.

[timothyl2184]

Thank you, I found the modulator easily with these pics/diagrams. I never noticed it before, partly because it's covered in a thick layer of primordial sludge and partly because I didn't know exactly what I was looking for . Now for the fix...

[msenousy]

Hello timothyl2184,
did the vacuum modulator resolve the problem? I have the same code401.
Thanks

[JohnGD]

Stick a MityVac to the hose going to the EGR valve. With a warm engine check the vacuum reading at idle and 2500 rpms.

[msenousy]

Thanks JohnGD,
and how much should it read?

[JohnGD]

At idle it should be 0 or close to it. At goes up to 2500 rpms expect increase to about 12 in/Hg with Port R teed to full engine vacuum. Otherwise expect 3 in/Hg and at about 3000 rpms it should increase to 5-6 in/Hg.

If you see only 0 at the EGR valve, then plug the hose back. Do the same check at Port Q of the modulator. (to see if the problem is with the EGR VSV). If the signal is there at the Port Q of the modulator but not there at the EGR valve then it's the VSV's problem.

Also, air blown into the hoses from the modulator's Ports P and R into the throttle body should flow freely into the throttle body. If these vacuum signal ports in the throttle body are blocked then the EGR valve won't work.

These are some quick checks. See how they work out. Otherwise we can go through some step-by-step checks later.

Originally Posted by msenousy

Thanks JohnGD,
and how much should it read?

[msenousy]

Originally Posted by JohnGD

At idle it should be 0 or close to it. At goes up to 2500 rpms expect increase to about 12 in/Hg.

If you see only 0 at the EGR valve, then plug the hose back. Do the same check at Port Q of the modulator. (to see if the problem is with the EGR VSV). If the signal is there at the Port Q of the modulator but not there at the EGR valve then it's the VSV's problem.

Also, air blown into the hoses from the modulator's Ports P and R into the throttle body should flow freely into the throttle body. If these vacuum signal ports in the throttle body are blocked then the EGR valve won't work.

These are some quick checks. See how they work out. Otherwise we can go through some step-by-step checks later.

I am not sure whether I have fully understood what you said. Here is what I did:
1. I attached the Mityvac, using a 3-way connector, to the hose on top of the EGR valve (i guess this hose goes to the vsv, I am not sure though).
2. When the engine was cold at idling, the vacuum read zero.
3. When the engine was cold at 2500rpm, the gauge read zero as well.
4. When the engine was warm an d at 2500 rom, the gauge read very low vacuum (around 3").

Now, i am not sure whether the above is correct and whether I am receiving the healthy readings. Also, when you mentioned connecting the Mityvac to port Q, was this also using 3-way connector and performing the above steps?

In the repair manual, it also says to disconnect port R and connect it directly to the intake manifold. I have no idea whatsoever where this intake manifold is?

thanks

[JohnGD]

That looks about right. Looks like your EGR control circuit and VSV are working. You can try the modulator test mentioned. However let's take some additional steps:

1. Try pulling 5-6 in/Hg on the EGR valve at idle. Does the engine run rough?

My prior mistake about 12 in/Hg, that's with teeing Port R to full engine vacuum so I'll update it. At 2500 it should be about 3" and at about 3000 it should be closer to 5-6 in/Hg which fully opens the EGR valve.

2. Tee the vacuum hose that goes to the modulator's Port R to the MAP hose (The MAP sensor is mounted on the firewall. You will need an extra vacuum hose or two). Now Port R gets full engine vacuum from the "intake manifold". With WARM engine at 2500 rpms now,

- a) do you see 12 in/Hg at the EGR valve?
- b) do you see the same reading at Port Q of the modulator? (connecting MityVac directly to Port Q)

If you don't see 12" at Port Q then look into the modulator some more. If the readings at Port Q and the EGR valve are different, then there is a vacuum leak between the modulator and EGR valve.

3. Remove the two modulator hoses that go to the throttle body in turn. Measure the vacuum at the two ports on the throttle body at idle and 2500.

What readings do you see at idle and 2500? Port P should see vacuum earlier than Port R. Right?

Originally Posted by msenousy

I am not sure whether I have fully understood what you said. Here is what I did:
1. I attached the Mityvac, using a 3-way connector, to the hose on top of the EGR valve (i guess this hose goes to the vsv, I am not sure though).
2. When the engine was cold at idling, the vacuum read zero.
3. When the engine was cold at 2500rpm, the gauge read zero as well.
4. When the engine was warm an d at 2500 rom, the gauge read very low vacuum (around 3").

Now, i am not sure whether the above is correct and whether I am receiving the healthy readings. Also, when you mentioned connecting the Mityvac to port Q, was this also using 3-way connector and performing the above steps?

In the repair manual, it also says to disconnect port R and connect it directly to the intake manifold. I have no idea whatsoever where this intake manifold is?

thanks

[msenousy]

Thanks a million for this detailed procedure. I will try it tomorrow and keep you posted.

Originally Posted by JohnGD

That looks about right. Looks like your EGR control circuit and VSV are working. You can try the modulator test mentioned. However let's take some additional steps:

1. Try pulling 5-6 in/Hg on the EGR valve at idle. Does the engine run rough?

My prior mistake about 12 in/Hg, that's with teeing Port R to full engine vacuum so I'll update it. At 2500 it should be about 3" and at about 3000 it should be closer to 5-6 in/Hg which fully opens the EGR valve.

2. Tee the vacuum hose that goes to the modulator's Port R to the MAP hose (The MAP sensor is mounted on the firewall. You will need an extra vacuum hose or two). Now Port R gets full engine vacuum from the "intake manifold". With WARM engine at 2500 rpms now,

- a) do you see 12 in/Hg at the EGR valve?
- b) do you see the same reading at Port Q of the modulator? (connecting MityVac directly to Port Q)

If you don't see 12" at Port Q then look into the modulator some more. If the readings at Port Q and the EGR valve are different, then there is a vacuum leak between the modulator and EGR valve.

3. Remove the two modulator hoses that go to the throttle body in turn. Measure the vacuum at the two ports on the throttle body at idle and 2500.

What readings do you see at idle and 2500? Port P should see vacuum earlier than Port R. Right?

[93celicaconv]

[msenousy]

My car model is Camry 1998.

[msenousy]

Here is what I got:

1. Try pulling 5-6 in/Hg on the EGR valve at idle. Does the engine run rough?

My prior mistake about 12 in/Hg, that's with teeing Port R to full engine vacuum so I'll update it. At 2500 it should be about 3" and at about 3000 it should be closer to 5-6 in/Hg which fully opens the EGR valve.

1. The engine died at around 2-3" of vacuum.
2. At both 2500 rpm and 3000 rpm around 2-3" at the EGR valve


2. Tee the vacuum hose that goes to the modulator's Port R to the MAP hose (The MAP sensor is mounted on the firewall. You will need an extra vacuum hose or two). Now Port R gets full engine vacuum from the "intake manifold". With WARM engine at 2500 rpms now,

- a) do you see 12 in/Hg at the EGR valve?
It gave around 16 in/Hg
- b) do you see the same reading at Port Q of the modulator? (connecting MityVac directly to Port Q)
No, abit higher (20 in/Hg)


If you don't see 12" at Port Q then look into the modulator some more. If the readings at Port Q and the EGR valve are different, then there is a vacuum leak between the modulator and EGR valve.

3. Remove the two modulator hoses that go to the throttle body in turn. Measure the vacuum at the two ports on the throttle body at idle and 2500.

What readings do you see at idle and 2500? Port P should see vacuum earlier than Port R. Right?[/QUOTE]

Port R: ZERO vacuum at BOTH idle and 2500 rpm!!!!!!
Port P: at idle = zero, at 2500rpm = 21 in/Hg.

for port R, I also measured directlty at the brass throttle to make sure that it is not the hose itself.

If the problem is at this throttle, how do I clean it? Can I just inject carb-cleaner into this opening or do I need to remove the duct connected to the throttle body and clean it.

Thanks a million and your help is highly appreciated.

Originally Posted by JohnGD

That looks about right. Looks like your EGR control circuit and VSV are working. You can try the modulator test mentioned. However let's take some additional steps:

1. Try pulling 5-6 in/Hg on the EGR valve at idle. Does the engine run rough?

My prior mistake about 12 in/Hg, that's with teeing Port R to full engine vacuum so I'll update it. At 2500 it should be about 3" and at about 3000 it should be closer to 5-6 in/Hg which fully opens the EGR valve.

2. Tee the vacuum hose that goes to the modulator's Port R to the MAP hose (The MAP sensor is mounted on the firewall. You will need an extra vacuum hose or two). Now Port R gets full engine vacuum from the "intake manifold". With WARM engine at 2500 rpms now,

- a) do you see 12 in/Hg at the EGR valve?
- b) do you see the same reading at Port Q of the modulator? (connecting MityVac directly to Port Q)

If you don't see 12" at Port Q then look into the modulator some more. If the readings at Port Q and the EGR valve are different, then there is a vacuum leak between the modulator and EGR valve.

3. Remove the two modulator hoses that go to the throttle body in turn. Measure the vacuum at the two ports on the throttle body at idle and 2500.

What readings do you see at idle and 2500? Port P should see vacuum earlier than Port R. Right?