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Q: Code P0400; EGR System

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The code on my Nissan Altima is only the P0400 code. However, I have cleaned out the valve and when I suck on the vacuum tube, the piston moves up and down inside the valve. None of the hoses are damaged. I had all my hoses and pipes replaces after an oil leakage to ensure none of them would be disintegrated by the residue. I am trying to narrow down what I need fixed, hopefully without needing to pay a diagnostics fee. From the research I have done if the EGRC Solenoid Valve was needing to be replaced I would have a P1400 code, however, I only have the P0400 code. The other possible part that would need to be repaired would be the temperature sensor. Yet, this seems to be infrequent for this issue.What part do I need to replace? Is my EGR valve working properly if the piston inside still moves up and down when I suck on it?

My car has 266500 miles.
My car has an automatic transmission.

A: If you checked the EGR valve and cleaned it...

If you checked the EGR valve and cleaned it, the first thing to do is to start and idle the engine and use a vacuum pump or source to pull open the EGR valve to see if it makes the engine run rough.

It should cause the engine to run rough if the passages are clear. In the EGR tube there is a temperature sensor that can be removed and cleaned of carbon. If it has carbon build up, it can cause inaccurate EGR readings and code P0400. Run engine warm and at around 2000 RPM's and see if EGR is being opened by the EGRC or there is vacuum on the hose to the EGR valve. Check the purge valve to see if it's leaking vapor all of the time.

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