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Thread: Verifying what data OBDII Mode 01, PID 01 returns

  1. #1
    Newbie preet's Avatar
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    Verifying what data OBDII Mode 01, PID 01 returns

    Hiya,

    I have a quick question regarding exactly what OBD Mode 01, PID 01 returns. It should be returning the status of certain monitors for various things in the car. There's a small (but important) disrepency between two descriptions of the data returned that I found online, and was hoping someone here could clarify.

    Source 1 (http://obddiagnostics.com/obdinfo/pids1-2.html) says that four bytes are returned, (A,B,C,D), with bits B0-B6 (excluding B3 and B7) used to indicate the status of monitoring tests. Further, each of the bits in bytes C and D are separate flags for the following monitoring tests (from bit0-bit7):
    Catalyst
    Heated Catalyst
    Evaporative System
    Secondary Air System
    A/C Refrigerant
    Oxygen Sensor
    Oxygen Sensor Heater
    EGR System

    Source 2 (http://en.wikipedia.org/wiki/OBD-II_PIDs) also says that four bytes are returned (A,B,C,D) with bits B0-B6 used to indicate the status of certain monitoring tests. B7 is excluded, but here B3 is used to indicate whether the vehicle is spark ignition (gasoline) or compression ignition (diesel). Based on this, the monitoring tests assigned to bytes C and D change:
    (c0-c7 tests [for spark ignition])
    Catalyst
    Heated Catalyst
    Evaporative System
    Secondary Air System
    A/C Refrigerant
    Oxygen Sensor
    Oxygen Sensor Heater
    EGR System

    (d0-d7 [for compression ignition])
    NMHC Cat Test
    NOx/SCR
    Boost Pressure
    Exhaust Gas Sensor
    PM Filter
    EGR / VVT System

    What's more, Mode $01, PID $0x41 (described in Wiki) is very similar to PID 0x01. You'd think, based on the description, that the data sent by both pids 0x01 and 0x41 would be the same.... but this isn't the case. The info in Wiki for PID 0x41 matches the data described by the other Source (obddiagnostics.com). Could someone clear up this difference?


    Regards

    Preet
    Check out my Frontend project!
    http://prismaticproject.weebly.com/blog.html

  2. #2
    Variable Bitrate
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    Bit B3 has been assigned to indicate Petrol or Diesel in the 2007 version of the spec.
    Wikipedia here has the latest/newest/correct information.
    Get a copy of Sae J1979 and all your questions will be answered.

    The information from obddiagnostics is out of date by something like 15 years or more.
    Pid 1F and following have been around for a long time now.
    Last edited by p2psmurf; 01-15-2012 at 06:13 AM.

  3. #3
    Newbie preet's Avatar
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    Sweet!

    Thanks a ton p2psmurf.
    Check out my Frontend project!
    http://prismaticproject.weebly.com/blog.html

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