Edmunds Answers



  • 0patience 09/19/10 3:30 pm PST

    "code shows excessive back pressure"

    The code saying excessive back pressure means nothing without proper diagnosis.
    Did they actually check the back pressure??
    The computer uses the value difference between the front and rear O2 sensors to determine back pressure, so if the cat is plugged, you have another problem somewhere else, causing the problem.

    We need to know what the EXACT fault code is, to be able to be of any help.
    What year, make, model and engine???

  • uontsom 09/19/10 11:14 pm PST

    I drive a 2002 pontiac grand prix GTP. 6 cylinder 3.8L. not sure if the mechanic said anything about a "code number" like when my 02 sensor went out. he just said when he ran a scan it showed excessive back pressure and that it was my cat converter....

  • 0patience 09/20/10 12:01 am PST

    As I said, the back pressure would have to be checked.
    It involves taking a measurement of the exhaust flow before the cat and after the cat.

    Without the fault code, we can't be much help on what to do.
    There are several fault codes that can direct a person to a cat efficiency failure and each one could lead a person in a different direction.
    Add to the fact that some cat efficiency codes may be a sensor or circuit and could direct a person to an O2 sensor circuit, exhaust leak or vacuum leak and not the actual cat.

    So, as you can see, we need the actual fault code number.


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