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I’ve had this P0401 EGR Insufficient Flow on my 96 Corolla for over 4 years now. Over the years I’ve replaced the vacuum modulator, recently replaced the VSV with a used VSV from eBay (I can return it if needed), and cleaned the EGR valve itself. Just yesterday I opened up the intake manifold and it was NASTY!! It looked pretty much exactly like in the pic in this thread: http://www.ericthecarguy.com/kunena/8-Service-and-Repair-Questions-Answered-Here/51172-p0401-96-toyota-corolla
I thought I had it fixed up, but the Check Engine light came on again today, same code once again. I guess I will check that tube on the EGR valve itself, like in that other thread. But man I REALLY hope I don’t have to drop $100+ on a new EGR valve. I did apply vacuum directly to the EGR valve with a vac pump and the engine started running rough as it should have. So the EGR valve itself is still able to operate. I just need to check that pipe which runs from the EGR valve up to the vacuum modulator.
I’ve been reading this series of articles on EGR systems and the P0401 code here:
Vacuum modulator EGR system description: http://www.motor.com/magazine/pdfs/082009_04.pdf
EGR system diagnostics: http://www.motor.com/magazine/pdfs/092009_04.pdfI actually need to pick up a vacuum gauge to properly test that VSV. But it also seems like that vacuum modulator a replaced a couple of years ago isn’t working properly. With vacuum applied to the bottom port, it should allow air to flow through from port Q, but mine does not.
Any other suggestions?
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So I acquired a vacuum test gauge and tried the VSV test procedures described in the Motor.com PDF articles and also in the Just Answer link above. Both VSV’s (original and the one I just got off eBay) both failed both tests. I suppose that’s the culprit.
When I apply vacuum to the inlet port of the VSV, no vacuum registers on the outlet port (on either one). When I blow air through the outlet port, air comes out the filter normally. But when the VSV is energized, no air comes out of the inlet port (on either one).
[quote=”PatrickGSR94″ post=122706]So I acquired a vacuum test gauge and tried the VSV test procedures described in the Motor.com PDF articles and also in the Just Answer link above. Both VSV’s (original and the one I just got off eBay) both failed both tests. I suppose that’s the culprit.
When I apply vacuum to the inlet port of the VSV, no vacuum registers on the outlet port (on either one). When I blow air through the outlet port, air comes out the filter normally. But when the VSV is energized, no air comes out of the inlet port (on either one).[/quote]
Keep us posted on your progress. 🙂
This doesn’t help the OP but it is something I’ve been thinking about – vehicles need more than one CEL. Lets say the CEL comes on, you know why, the engine still runs great and it is not worth fixing. Even if you live where no smog test the light is on and if another code gets set, something important, you never know it because you are ignoring the light. The vehicle needs a method of signaling the owner that additional codes have been set.
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