Question about 1996 Toyota Tacoma

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Emission problem o2 sensor/egr valve?

My engine light is on and the codes are telling me its the O2 sensor and/or the egr valve....
how do i determine WHICH one it is and how do i fix it?

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  • valleyofthes Dec 04, 2008

    the code is p0401 egr has insufficient flow.... can you clean the egr valve?

  • valleyofthes Dec 04, 2008

    hello ASEtech,

    do i have to replace the egr valve or can it be cleaned?

  • valleyofthes Dec 04, 2008

    thank you toyota ed....

    4 cyl !!

  • Toyota Ed May 11, 2010

    Please provide a valid e-mail address, I will send it out ASAP.

  • Toyota Ed May 11, 2010

    Note to "ASEtech": Right, and WRONG, Sir.

    Valley: If this gentleman had the extensive background that I have, he would have mentioned that there are actually 5-6 things that cause the condition. EGR vacuum switching valve, EGR modulator valve, exhaust temeperature sensor, etc etc etc.

    If you EGR valve was stuck open, the vehicle would not idle.

    If you would like, I can send you the entire diagnostic tree to determine the exact cause of your issue. 4 or 6 cylinder?

  • Toyota Ed May 11, 2010

    Please report the exact codes that were given to you. Thanks.



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Codes do not tell you what is wrong. They only tell you if there is a problem with a specific system/circuit.
From the information you have given it sounds like you might have a problem with the EGR valve which is causing the O2 sensor codes. There is no way to tell for sure but this is probably the most likely cause of your problem.

Here is a website that has a lot more information along with videos about how different sensors work:

Posted on Dec 04, 2008

  • Steve
    Steve Dec 04, 2008

    If Toyota Ed had the extensive knowledge that I do he would know that there are more than 5-6 things that can cause this code. He would also know that with this particular code the most likely cause of the problem is that either the EGR passageways are blocked or the EGR valve is bad. This does not mean that there aren't a lot of other things that can cause this code. It means that it is the MOST LIKELY cause of the problem.



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To BIGHWEELS197, take your car to AutoZone and have them scan the computer - they'll do it for free, whereas the dealer will charge an hour's labor. Post the codes here and we can determine the problem.

To wjcomet, here are your code definitions:

P0133 O2 Sensor Circuit Slow Response (Bank 1 Sensor 1) - this means that the primary O2 sensor on the bank of cylinders with cylinder number 1 in it is not heating up quickly enough. The heating element is eventually getting it to temperature (it has to be heated up to work) but it's getting to be too long to heat up, which can fail you for cold-start emissions. You'll have to replace this sensor eventually.

P0341 Camshaft Position Sensor “A” Circuit Range/Performance (Bank 1 or Single Sensor)

This indicates a problem with your cam angle sensor. It could be that the sensor's pickup is not working right anymore (this does happen) but it could also be because your O2 sensor isn't getting to temperature soon enough and excess emissions are being detected, the car's computer may think that the cam position is off. If the cam isn't timed right, excess emissions can happen, so the computer may believe that's what is happening. I wouldn't be surprised however if the O2 sensor that's going bad is causing this code as well.

P0404 Exhaust Gas Recirculation Control Circuit Range/Performance

Indicates a failure of the EGR valve. Again, there's a chance that the failing O2 sensor can trigger this.

P1404 is a manufacturer-specific auxiliary emissions control failure code. I don't have access to that code's definition for your car, but again it's likely to be a result of the O2 sensor fault that you're having, since it's emissions-related and the O2 sensors are the main controllers of emissions on a car.

My advice would be to change that O2 sensor, have the codes reset, and see which ones, if any, return. If none come back, you likely had only the O2 problem and that fault caused the other codes as well. If one or more of the codes returns, we'll have to troubleshoot those individually.

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