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Mercedes Benz





   Diagnostic Systems

    OBDI - On-Board Diagnostics I; a 1988 regulation requiring a MIL, engine diagnostics,
                  non-standard diagnostic codes, non-standard diagnostic connector & electrical interface,
                  and volatile fault memory

    OBDII - On-Board Diagnostics II; a 1996 regulation requiring standardized diagnostic codes and
                  a uniform connector per SAE J2012, with emphasis on emissions system failures and
                  complying with J1850 or ISO 9141-2 protocol, a MIL, & a non-volatile fault memory

   Common Generic OBDII Fault Codes (DTC)

    X1XX, X2XX - Fuel & Air Systems
    X3XX - Ignition System
    X4XX - Emission System
    X5XX - Auxilary Functions
    X6XX - Engine Control Module Functions
    X7XX - Transmission Interface Functions
    1XXX - OEM Proprietary
    XXXZ - Same type of fault, Z - specific fault location/value

    0100 - Mass Air Flow Sensor (MAFS)
    0105 - Manifold Abosolute Pressure (MAP)
    0110 - Intake Air Temperature (IAT)
    0115 - Engine Coolant Temperature (ECT)
    0120 - Throttle Position Sensor (TPS)
    0130 - O2 Sensor, Bank 1 - Front Sensor
    0140 - O2 Sensor, Bank 1 - Rear Sensor
    0150 - O2 Sensor, Bank 2 - Front Sensor
    0160 - O2 Sensor, Bank 2 - Rear Sensor
    0200 - Injector Circuit
    0230 - Fuel Pump Circuit
    0300 - Random Cylinder Misfire
    0330 - Knock Sensor (KS)
    0335 - Crankshaft Position Sensor (CKP)
    0340 - Camshaft Position Sensor (CMP)
    0400 - Exhaust Gas Recirculation (EGR)
    0410 - Secondary Air Injection (SAI)
    0420 - Catalytic Converter Efficiency, Bank 1 (TWC)
    0430 - Catalytic Converter Efficiency, Bank 2 (TWC)
    0440 - Evaporative Emission Control System (EVAP)
    0500 - Vehicle Speed Sensor (VSS)
    0560 - System Battery Voltage
    0605 - General Control Circuit (ECM)
    0650 - Malfunction Indicator Lamp (MIL)

    1. OBDII DTCs are accessed via the diagnostic link connector (DLC),
        located in the passenger compartment near the steering column.
    2. OBDII DTCs are not cleared by ECM/battery removal.
    3. An OBDII MIL is reset by ECM/battery removal.
    4. Most OBDII scanners provide a description of the generic DTCs,
        in addition to the numeric code, but not for the proprietary DTCs.
    5. Some OBDII DTCs do not set the MIL but are stored as pending.
    6. Some OBDI/OBDII DTCs may accessed via special sequences and viewed by a flashing MIL.

   OBDII Modes

    Mode 1 - Output of input/output signals, status & calculated values
    Mode 2 - Output of Freeze Frame data
    Mode 3 - Output of stored faults
    Mode 4 - Erasure of fault memory
    Mode 5 - Output of O2 data
    Mode 6 - Output of non-continuous readiness tests
    Mode 7 - Output of continuous readiness tests
    Mode 8 - Requests control of manufacturer specific ECM systems
    Mode 9 - Reports VIN and ECM calibration info
    Mode 10 - Output of permanent emission faults not having been ECM verified as corrected

   Basic OBDII Readiness Codes

    Non-Continuous Tests

     - Three Way Catalytic Converter (TWC) Effeciency
     - Fuel Tank Ventilation (EVAP)
     - Secondary Air Injection (SAI)
     - Oxygen Sensors
     - Oxygen Sensor Heating
    Continuous Tests
     - Fuel System (TRIM)
     - ECM Faults (DTC)
     - Cylinder Misfire

    1. Completed after two trips; Trip - consists of 3 main cycles (Warm-up, Driving, & Evaluation)
           Warm-up Cycle - SAI, EVAP, (from cold start to operating temperature, 2 min. minimum)
           Driving Cycle - O2 Sensors/Heating, TWC, TRIM, (2 min. idle, 5 min. drive, 2 min. idle)
           Evaluation Cycle - Diagnosis of All ECM Systems
    2. Completed (Set) Prior to an Emissions Test.
    3. Accessed via the OBDII Connector (DLC).
    4. Reset by a DTC clear, a battery disconnection, or an ECM removal.
    5. Some non-continuous tests, e.g. SAI & EVAP, can be run ("Short Test") via special scanners.
    6. Some early OBDII vehicles, e.g. Porsche 993 ('96), may require three trips as in #1 above
        versus two trips for later vehicles ('97), e.g. updated firmware, and/or may also require a waiver
        from the emissions regulatory agency. Also, some of these early vehicles may reset the readiness
        codes at engine shut-down before completion of a trip requiring the starting of another new trip.
        If a cycle fails, e.g. EVAP or SAI, during a subsequent trip but before completion of all necessary
        trips, the required number of trips must be restarted.
    7. During a trip, code 026 (Oxygen Sensing, Area 2 cylinders 1-3) and/or 034 (Oxygen Sensing,
        Area 2 cylinders 4-6) may occur which indicates the FRA long term trim has exceeded its limit,
        indicating an overall lean condition.
    8. The Secondary Air Injection test on the Porsche 996/997 with the front wide band O2 sensors
        must achieve a voltage level above 1.00 volt and typically more than 1.5 volts to pass within
        the required time limit. Typically the front wide band O2 sensors will indicate about 2.0 volts
        to 2.4 volts lean condition under a no-load deceleration from 3K RPMs to idle. Under normal
        closed-loop operation the O2 sensors will typically vary +/-.30 volts.

   Porsche 993 Cycle Flag Basics

    1. CAT Efficiency - using rear O2 sensors, must drive @ medium load & RPMs < 2500
    2. O2 Sensor Aging - monitors O2 sensors' waveform period, must drive @ 2 load ranges,
        i.e. light/medium loads
    3. SAI - monitors front O2 sensors' minimum voltage, done @ idle or via Short Test
    4. Tank Venting - monitors tank vacuum, done @ idle or via Short Test
    5. Adaptation - monitors TRAs & FRAs, done @ idle RPM & @ 1500 < RPM < 3000
        for 15 seconds @ each RPM (driving not required)

     Notes: The above cycle flags when completed (set) comprise one trip. After completion of the
     1st trip, the engine is stopped (cycle flags reset) & restarted to begin the 2nd trip, followed by
     a 3rd trip if necessary. A cold engine is required between trips for the SAI test if not using the
     Short Test (Porsche diagnostic tool). If the engine is stopped, e.g. stalled, before completion
     of the trip, the trip must be restarted from the beginning & all completed cycle flags are reset
     for that trip. Once all the necessary trips have been completed, the readiness codes will be
     indicated by an OBDII scanner. The exception to this is the '98 993, where only one trip is
     required over numerous days, and the readiness codes appear as they complete using a generic
     OBDII scanner. For the pre-'98 993s setting of the readiness codes is extremely difficult without
     the use of a Porsche diagnostic tool, e.g. Hammer, PST2, or PIWIS.


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