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egr problem code p0401

Discussion in '1st Gen. Tacomas (1995-2004)' started by allen1992, Mar 14, 2013.

  1. Mar 14, 2013 at 2:43 PM
    #1
    allen1992

    allen1992 [OP] Active Member

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    allen
    Zephyrhills, Florida
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    I have a 99 tacoma and i have a engine code p0401 which is insufficient EGR (exhaust gas recirculation) flow. i tested mt egr today at work and it works perfect i checked all the passages and they are all clean. What else can i check to get rid of this engine light because i will clear the code and it comes back 2 days later and i cant stand check engine lights! please help!
     
  2. Jun 5, 2013 at 5:18 AM
    #2
    zacharypaul89

    zacharypaul89 Eat right, be fit, die anyway

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    Zach
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    So many people, including myself, have had this problem. Ive taken my EGR off twice and cleaned it out, I've tested it with a vacuum and it worked perfectly, I've cleaned out all the hoses going into it, the metal hose behind it, and the f***ing light still comes on. I still get about 22 mpg, so I said screw it. The light will randomly turn off for a while, but it ALWAYS comes back on. If you find a permanent solution, let me know!
     
    Colchicine likes this.
  3. Jun 5, 2013 at 6:11 AM
    #3
    BamaToy1997

    BamaToy1997 Wheel Bearing Master

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    Understanding how the system checks EGR operation is a big part of diagnosing that code. Typical EGR flow codes (Especially the P0401) are not PHYSICALLY measured with a sensor. A electrical problem, whether due to sticking or shorted EGR will usually set a P0406 code (but not always)

    To test for a P0401 the computer will monitor your Pre-cat O2 sensor. (Also called your A/F sensor) and when the computer activates the EGR valve it expects to see a specific difference in the signal from the A/F sensor. If it does not see what it expects to see for 2 drive cycles, it will turn on the CEL and you will find the P0401 code. Even if the passages are perfectly clean, you can still get a P0401 code from:

    Bad EGR valve (sticking, electronic failure)
    Bad A/F sensor (failed sensor, dirty sensor, bad connection)
    Internal failure of ECU
    Wiring problems (Bad connection, shorted wire, etc)

    In the case of a mechanical EGR, vacuum problems can also be a factor (poor quality vacuum, vacuum control, etc)
     
  4. Jun 5, 2013 at 7:17 AM
    #4
    wolfgang123

    wolfgang123 Well-Known Member

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    maybe a sensor since its intermittent like that
     
  5. Jun 5, 2013 at 11:06 AM
    #5
    tan4x4

    tan4x4 Well-Known Member

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    I have the exact same problem with my 2.7, just after I bought it. I removed and cleaned the valve, replaced the modulator (with used) but did not clear the P0401. Finally, I removed the EGR temp sensor (on the intake manifold near the EGR valve), cleaned the tip really good, and re-installed it. This cleared the P0401. Seven months later, the code returned, and I cleaned it again. I can live with this, rather than spend $$$ on a new sensor.
     
    Colchicine likes this.

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