CEL on!

[astroboy224]

i went to my local auto zone, and i had them read the codes because the engine light was on. they told me there was something wrong with the EGR system. the guy just told me to clean it out, and i never did. so i recently checked the exhaust vacuum madulator and it was really dirty, and then i checked the EGR valve and it was also clogged. so i cleaned it and reset the ECU and about 30 mins later, the light cmae back on! any help? thanks!

[kickfli12]

cant give much help if we dont have the code(s). have the codes read again and write them down, then post the codes and we can go from there

[astroboy224]

Dang...i don't remember what the code was. If i remember right...it was P0401. But tomorrow morning i will go get the codes checked again.

[kickfli12]

if that is the code thats the EGR low flow code. do a thorough cleaning of the EGR system and go from there. i mean take the intake manifold apart and everything.

[astroboy224]

sweeet. i will go get the codes again in the morning to double check before i mess with the intake manifold! ill keep you updated!
thanks!

[astroboy224]

Alright well i went this morning to get the codes read. The code indeed was 'P0401: exhaust gas recirculation low flow detected'
So I'm going to attempt to clean the intake manifold like you said.

[astroboy224]

freakin A. i give up for now...i started taking apart the intake manifold...i took off the TB and then i was gonna start to loosen the bolts that hold the two halves of the Intake manifold together, when i pulled the longer hose of the 2 hoses that go from the intake manifold to the engine heaad..it snapped. im guessing it was really old and rotten and when i flexed it..it snapped? now what?! i ghetto rigged it and wrapped it with duct tape til i go back to get some tubing...ugh fml..

[astroboy224]

my ghettto rig worked and got mee to autozone. so i got the new hose. put it on and cleaned the intake manifold as best i could. i pulled the EFI fuse to reset the ECU...but about 3o mins later...the engine light came back on...so now what?!

[kickfli12]

Have you verified that all your components are working correctly?

[speedy25]

you will NOT get it cleaned without removing all the EGR piping and cleaning it all out.

-SP

[astroboy224]

What components are you referring to? I have checked the exhaust vacuum modulator and its fine. The egr valve has been replaced and i cleaned it recently. What else is there?

[Rich L]

I had the same CEL a year or two ago. In summary, here is what I learned.

The VSV valve (vacuum switching valve) is notorious for intermittently failing. It switches open (air flows from one vacuum valve to the next) when 12VDC is applied to the terminals. Seems like air vents to the bottom when de-energized.
Looks kindof like this.

The EGR modulator includes an internal plastic diaphragm that can get a pin hole. The unit must be replaced if this happens. Apply a small vacuum or blow/suck on the bottom valve and see if it holds pressure.
Looks similar to this

You may also have a vacuum leak. The 7th gen uses a MAP sensor to monitor the EGR system (when equipped with an EGR). The MAP sensor is not very sensitive. I was told by my mechanic that a CEL for low EGR flow on the 7th gen Corollas means close "no" EGR flow.

EGR valve can fail, but it is rare. Unfortunately, this is the first thing most people replace. Most of the time the CEL comes back. Put a vacuum on the hose going to the EGR modulator and see if the motor stumbles on idle.

In my case, it was a lot of carbon between the EGR and the intake manifold. Take the manifold off and clean out all the pockets. Good place to start is here.

[astroboy224]

Originally Posted by Rich L

I had the same CEL a year or two ago. In summary, here is what I learned.

The VSV valve (vacuum switching valve) is notorious for intermittently failing. It switches open (air flows from one vacuum valve to the next) when 12VDC is applied to the terminals. Seems like air vents to the bottom when de-energized.
Looks kindof like this.

The EGR modulator includes an internal plastic diaphragm that can get a pin hole. The unit must be replaced if this happens. Apply a small vacuum or blow/suck on the bottom valve and see if it holds pressure.
Looks similar to this

You may also have a vacuum leak. The 7th gen uses a MAP sensor to monitor the EGR system (when equipped with an EGR). The MAP sensor is not very sensitive. I was told by my mechanic that a CEL for low EGR flow on the 7th gen Corollas means close "no" EGR flow.

EGR valve can fail, but it is rare. Unfortunately, this is the first thing most people replace. Most of the time the CEL comes back. Put a vacuum on the hose going to the EGR modulator and see if the motor stumbles on idle.

In my case, it was a lot of carbon between the EGR and the intake manifold. Take the manifold off and clean out all the pockets. Good place to start is here.

I did check the EGR modulator and the air flow is fine. i cleaned the EGR valve cause it was really clogged. and then i did that Intake manifold cleaning using that same DIY you had a link too. and there was a lot of carbon blocking the hole to the EGR valve. so i got that out as best i could. and idk about the MAP sensor and the VPV...but if you said they dont go bad that easy...then im not too worried its that. but why would the CEL come on...?

[Rich L]

I did check the EGR modulator and the air flow is fine. i cleaned the EGR valve cause it was really clogged. and then i did that Intake manifold cleaning using that same DIY you had a link too. and there was a lot of carbon blocking the hole to the EGR valve. so i got that out as best i could. and idk about the MAP sensor and the VPV...but if you said they dont go bad that easy...then im not too worried its that. but why would the CEL come on...?

The VSV do go bad. Actually, I would guess they are the most likely part to fail of the three (EGR, modulator, VSV). The problem is they fail intermittently. Will fail to open a few times triggering a CEL, but will work most of the time (and ALWAYS when tested .

The MAP sensor should not go bad. The vacuum hose is a larger diameter hose connected to the bottom of the throttle body. If the hose is attached, you are probably OK.

If you cleaned the intake and plumbing to the EGR really well, I would check for vacuum leaks in the EGR system. Replace EGR vacuum hoses with the proper sized vacuum lines. Sometimes the aftermarket suppliers do not provide the correct size. They won't hold fit as well as the Toyota stuff. Just make sure you get some that fit well. Shouldn't cost much more then a few bucks.

If that fails, the next place I would go is the VSV valve. Would suggest a junkyard first then try a new unit if that fails. While you are at the junkyard, pull the modulator along with the VSV. Check it first to ensure if the plastic diagram is good. Buy it and replace it while you are in there. Total should be probably $10-20.

Last step would be replacing the EGR. Again, this can be easily tested by putting a vacuum on the hose that goes between it and the modulator (simply sucking on that hose if you don't have a vacuum pump). The car should stumble and/or die. If it does, IMHO don't waste your money on a new EGR.

[astroboy224]

Originally Posted by Rich L

The VSV do go bad. Actually, I would guess they are the most likely part to fail of the three (EGR, modulator, VSV). The problem is they fail intermittently. Will fail to open a few times triggering a CEL, but will work most of the time (and ALWAYS when tested .

The MAP sensor should not go bad. The vacuum hose is a larger diameter hose connected to the bottom of the throttle body. If the hose is attached, you are probably OK.

If you cleaned the intake and plumbing to the EGR really well, I would check for vacuum leaks in the EGR system. Replace EGR vacuum hoses with the proper sized vacuum lines. Sometimes the aftermarket suppliers do not provide the correct size. They won't hold fit as well as the Toyota stuff. Just make sure you get some that fit well. Shouldn't cost much more then a few bucks.

If that fails, the next place I would go is the VSV valve. Would suggest a junkyard first then try a new unit if that fails. While you are at the junkyard, pull the modulator along with the VSV. Check it first to ensure if the plastic diagram is good. Buy it and replace it while you are in there. Total should be probably $10-20.

Last step would be replacing the EGR. Again, this can be easily tested by putting a vacuum on the hose that goes between it and the modulator (simply sucking on that hose if you don't have a vacuum pump). The car should stumble and/or die. If it does, IMHO don't waste your money on a new EGR.

Alright well i will take a look at the vacuum hose to see if its attached, and if thats an ok..then i will check if there are any leaks. but this is getting frustrating.