I am getting a P0402 EGR "A" Flow Excessive How to find exact cause

Tiny
PCMENTOR29
  • 1996 TOYOTA AVALON
  • 160,000 MILES

If flow is excessive I tried fixing for a sticking egr valve. I vacuum it up and tap the valve a little with a screwdriver handle. I also think it may be the Thermo sensor(see in pics). I have another thermo sensor from junkyard. What are the values I test for on the thermo sensor? What other causes of this problem can you think of? There is no valve position sensor as you can see. I believe the thermo sensor is the only trigger for the ECM to say the flow is too cold or excessive? I am not sure on the function read by ECM can you clarify please? Thanks

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Monday, October 15th, 2012 AT 3:07 AM

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Tiny
PCMENTOR29
  • MEMBER

ALso I did a road test with vac gauge attached. At acceleration it would read between 5 -9 inHg vacuum. At WOT no vac and at no throttle no vac. This seem correct unless the value should be 5 inHg and any higher the modulator is at fault. Please let me know the correct vac reading. Thanks

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Monday, October 15th, 2012 AT 3:26 AM
Tiny
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If you pull a vacuum on the valve with a hand vacuum pump and then release the vacuum does the egr valve stick open?I also posted the trouble tree for that code. Let me know what you find.

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Monday, October 15th, 2012 AT 3:40 AM
Tiny
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Thanks I will try.

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Monday, October 15th, 2012 AT 11:50 AM
Tiny
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Your welcome keep me posted.

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Monday, October 15th, 2012 AT 5:13 PM
Tiny
PCMENTOR29
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If you pull a vacuum on the valve with a hand vacuum pump and then release the vacuum does the egr valve stick open? No I did it 5 times(to 20 psi) and it snapped closed each time.

Also on the EGR Modulator, the filter on top was hard side down. I heard the hard/rough side goes up and the soft side down. There was a carbon deposit on the filter that may have plugged the vent hole under the filter. I will try driving for a while and see if the soft side down clears the high flow problem.

Also I tested the EGR temp sensor and got 150KOhms at 89.8 degF measured on the part. This seems ok as it's more than 2500 ohms. I also tested a spare sensor and got 273kOhms at 69.8degF. Which seemed ok.

Also I am confused as to how to carry out the following test procedure. How can I tell if theres restricted flow with the noise of the engine reving to 3500rpm? Is there a trick to it? Thanks

EGR VACUUM MODULATOR
1. Mark vacuum hose locations and disconnect vacuum hoses from EGR vacuum modulator.
See Fig. 26. Block ports "P" and "R" on EGR vacuum modulator. See Fig. 25.
2. Apply air pressure to port "Q". See Fig. 25. Air should flow freely through air filter side
of EGR vacuum modulator.
3. Start and operate engine at 3500 RPM. Repeat test procedures in steps 1) and 2). Strong
resistance of airflow should be felt. Replace EGR vacuum modulator if strong resistance is
not felt. Reconnect vacuum hoses to proper locations.
NOTE: When testing EGR vacuum modulator, it may be necessary to
monitor engine RPM by using scan tester. For scan tester
connections, see IDLE SPEED & MIXTURE in ADJUSTMENTS article.
NOTE: Ports "P" and "R" are the double ports on side of EGR vacuum
modulator. Port "Q" is single port on side of EGR vacuum
modulator

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Wednesday, October 17th, 2012 AT 9:35 AM
Tiny
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Should I used 30psi air from a compressor and also remove the cap and filter to do the EGR Modulator Test? Is it even worthwhile to do this test? Maybe better to check if filter/port is blocked like I found. I am hoping it was the solution. Thanks.

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Wednesday, October 17th, 2012 AT 9:48 AM
Tiny
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I would continue on the path your going and see how it turns out looks like you most likely found the problem. Keep me posted.

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Thursday, October 18th, 2012 AT 3:30 AM
Tiny
PCMENTOR29
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I drove it 200 miles today and no code. I parked it for 2.5 hours it cooled down and then drove 7 miles no code. That's great it may be solved. Thanks for your help.

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Friday, October 19th, 2012 AT 4:27 AM
Tiny
PCMENTOR29
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I donated $2, I hope you can buy a Mountain Dew with it. Thanks

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Friday, October 19th, 2012 AT 4:32 AM
Tiny
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Thanks for the donation did you donate it to this question?Also how did you know I liked mountain dew?

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Friday, October 19th, 2012 AT 5:25 AM
Tiny
PCMENTOR29
  • MEMBER

I don't know if I donated to the question or not. I don't think I saw how to donate directly to the question. How can you?

Problem still exists as of 1:30 PM Friday Oct 19 2012. P0402
After sitting overnight I started it and check lite came on before I was warmed up. I read about this issue, how it throws code before it warms up but I will have to find where. I have the old EGR Modulator, it's ugly but I will switch it tonite and see tomorrow if the code reappears. I replaced the old Modulator with a junk yard pull back in June. I think it may not be the problem since I just started having this code a week ago, but I will switch it back to see. Thanks

Hey Mountain Dew has the most caffiene and I like it too.

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Saturday, October 20th, 2012 AT 2:19 AM
Tiny
PCMENTOR29
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I still need help with the EGR Modulator 3500 RPM test, ie how to apply air and to be able to tell it the flow's restricted. Also I will check the hose at the bottom of the Modulator to see if cracked. How does the bottom hose supposed to work? Does it have pressure or vacuum? How much? Thanks

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Saturday, October 20th, 2012 AT 2:27 AM
Tiny
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Let me know what happens with the swap.I not sure how to donate on the question we just did a major site grade and relaunch still learning how to make my way around. Also mountain dew is the best I have been drinking it for a long time.I also have a cool light up mountain dew clock from the early 70's.

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Saturday, October 20th, 2012 AT 2:33 AM
Tiny
PCMENTOR29
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That clock is cool. Probably worth something to a collector.

I have switched the modulators. The round filter element on top I studied for a while and I think it does go hard side down. There are two little slits at the top of the modulator that would plug up if the hard side was up.
I am going to see if there is vacuum at the EGR valve when the engine is cold also tomorrow. I think it's supposed to be off below 122deg F. That would kind of make sense since the code throws when the engine is warming up.
Thanks

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Saturday, October 20th, 2012 AT 3:33 AM
Tiny
PCMENTOR29
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Can you tell me why they say to connect a jumper (in the attached pages)? What does it accomplish? Thanks

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Saturday, October 20th, 2012 AT 4:29 AM
Tiny
PCMENTOR29
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Can you please delete the two pages in my previous reply. They may be copyrighted.

OK I let the engine cool down to room temp. Then with vac gauge attached to egr valve vac port, It didn't move at first driving then after temp gauge rose the movement was 3 " Hg vacuum and after it warmed up the same. Last road test I was getting 5-9 "hg on the gauge. Maybe the original(non-junkyard part) modulator works right. I will have to drive it a little bit to see. Also I read that with the P0402 the ECM doesn't turn the light on when it occurs. It waits till the next drive and if conditions are still bad then it throws the code.I think that's why the light came on just as it warmed up previously. My only holdup now is verifying which way the filter goes in the EGR Modulator. It probably doesn't matter though. If the code persists tomorrow, I will check drive test with vac gauge to see if the Hg went up. Thanks.

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Saturday, October 20th, 2012 AT 10:29 AM
Tiny
PCMENTOR29
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The original Modulator won't hold pressure on the diaphragm so I switched back with the junkyard modulator and fresh hoses on the EGR system, I could not find a good size hose for the bottom hose but the existing hose is tight and no cracks. Now on road test while looking at Vac gauge the vacuum goes up really hi17"Hg, Then while parked rev to 2500 gives 17"Hg and 3700 RPM gives max of 20"Hg which must be manifold vacuum. Double checked each hose to diagram.

How can I further bench test the EGR Vac. Modulator? Should I ask this in a new question? The new EGR Vac. Modulator is $80 at Autozone and Toyota. Can you guys save me from buying a part when I don't need to? I will donate more if you can. I was thinking of cutting open the orig modulator to see if I can figure out how it works. There's a detailed 4 picture description of it in my Haynes manual. I will study it somemore while waiting for your reply. Thanks

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Sunday, October 21st, 2012 AT 2:09 AM
Tiny
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Here is what I have on testing the egr modulator let me know what you find.

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Sunday, October 21st, 2012 AT 2:19 AM
Tiny
PCMENTOR29
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Thanks for your reply, I am going to get a new modulator Sunday afternoon. I was worried about how to test the backpressure pipe which connects to the bottom of the modulator. First of all it's really clean, no carbon visible from the top. Then I hooked my vac tester which has a psi scale also. I disabled the EGR valve and ran the engine at 2500 and 3500 rpm, the most backpressure I got was 1.5 psi which I found to equal about 3 inHg in vacuum levels which seems ok. Also I blew about 40 psi compressed air into the small pipe and it did not sound clogged or partially clogged it flowed well. So at this point the junkyard modulator somehow is passing almost manifold pressures to the EGR valve. And my original modulator is cut open to look at, it has a hole in the diaphragm, maybe caused by someone poking a pin into the filter port at some point. Thanks for your help again.

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Sunday, October 21st, 2012 AT 5:09 AM
Tiny
PCMENTOR29
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I forgot to add: The only thing I can think of is wrong with the modulator is the spring went bad. Or if somehow it was worked on wrong by cleaning and reaming the pipes or a stiff diaphragm. Thanks

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Sunday, October 21st, 2012 AT 5:12 AM

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