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P0401 won't go away

  #1  
Old 11-25-2017, 03:44 PM
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Default P0401 won't go away

I had this Camry for a couple years before my first check engine light came on. It's P0401, for "EGR "A" Flow Insufficient". I had replaced the EGR valve since it was bad, cleared the computer, and it still comes back. Even after a reset (battery had died after sitting for a week, bad battery anyway).

What else should I check?
 
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  #2  
Old 11-25-2017, 08:19 PM
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What type of engine, 4 cylinder or V-6?

The code is stating not enough exhaust gas is being recirculated into the intake of the head.

Are you doing the repairs yourself?

A few things to check:

Were the gas intake and exhaust ports to the valve cleaned of carbon?

Vacuum hoses used in the system for leaks.

If the EGR valve has a temperature sensor check this.

Wiring to VSV and temp sensor (if used).

The EGR system is turned on/off by an electric vacuum valve (VSV). Is this valve working OK? EGR OFF when unpowered. ON when powered(12v) to let engine intake vacuum go to EGR modulator.

The EGR valve movement is controlled by a vacuum controlled modulator valve. Check the valve for proper operation.

There are a few threads below in Related Topics on this code.
 
  #3  
Old 11-25-2017, 09:10 PM
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I saw the related topics after I posted. I did a search, but I searched for EGR rather than the error code. I felt a little dumb after that.

However, it's a 2000 Camry, 4 cylinder. I'm doing the repair myself. It's been a while since I had it off and I don't think I did clean it of any carbon. There were no wires to the EGR, just a vacuum hose and mounting directly to the intake, I remember that well because it was a royal PIA..
 
  #4  
Old 11-25-2017, 10:06 PM
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The replaced EGR valve varies the amount of exhaust gas that is routed between the exhaust system and engine intake. Under certain conditions such as idle the valve is closed.

Carbon can build up in the exhaust intake, exhaust ports to the valve or on the EGR valve. The carbon can limit the flow of exhaust.

The EGR valve is moved by a vacuum powered built-in diaphragm connected to the valve. Vacuum to the EGR valve is modulated by the EGR modulator valve which also has a diaphragm. This modulation controls the EGR valves position.

The modulator has two vacuum connections and compares them to move the modulator valves position and with this amount of vacuum to the EGR valve.

The EGR system is turned on/off by a VSV valve the turns the vacuum to either the modulator or EGR valve off (depending on car).

A test of the EGR valve is to bypass the modulator and connect the EGR valve vacuum hose directly to full vacuum. This will open the valve. If the valve is working OK, opening the EGR valve at engine idle should stall the engine or at least cause it to run very poorly.
 
  #5  
Old 12-27-2017, 02:44 AM
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I got the same code and it turned out that the EGR modulator valve was clogged and causing the problem.
 
  #6  
Old 07-11-2018, 06:35 PM
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Sorry for the extremely late reply on the topic.

I replaced the EGR modulator valve, and the check engine light went away and stayed off for about 2 weeks. Then it came back for the same code. I went back to ignoring it for the next 2 months, and it magically went away on its own again about a month ago, and hasn't came back on.
 
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