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.
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
- Three Way Catalytic Converter (TWC) Effeciency
- Fuel Tank Ventilation (EVAP)
- Secondary Air Injection (SAI)
- Oxygen Sensors
- Oxygen Sensor Heating
- 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. 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.
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