On Board Diagnostics II

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On Board Diagnostics II

• What is OBD II?
• What is its purpose?
• Active and passive tests
• Monitors
• DTCs
• Generic OBD II data

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OBD II

• On board diagnostics originated in 1980s
• OBD I mandated for vehicles sold in Calif. in
  1988
• MIL to alert driver of malfunction
• Ability to record and transmit DTCs
• Monitored sensors for opens and shorts
• OBD I did not monitor
• Catalyst efficiency
• EVAP system leaks
• Catalyst damaging events such as misfires
• OBD I did not protect catalyst from damage by
  incorrect fueling or misfire

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What is OBD II

• Federal regulations for automobiles produced for
  sale in 1996
• Some manufacturers began to phase in OBD II as
  early as 1994
• Established federal test procedure for exhaust
  emissions and required on-board monitoring of
  emission control systems for correct operation
  and efficiency

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Purpose

• Designed to detect vehicle problems that can
  cause increased emissions
• Alerts driver of emission related problems
• Standardization
• DTCs
• Scan tool interface
• MIL operation
• DLC shape and location
• DLC now provides power and ground for scan tool
• Performs active and passive tests on emission
  systems

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Tests

• Active tests
• PCM changes something and measures response
• Passive tests
• Watches components during normal operation, but
  does not take active role in test process

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Monitors

• Tests performed by diagnostic system to check
  performance of various components and subsystems
• If a component or system failure is detected that
  can increase emissions, MIL is illuminated and
  DTC will set
• Continuous any component or subsystem that has
  catalyst damaging potential
• Non-continuous performs once per trip once
  monitor runs to completion it does not run again
  until next drive cycle
• Trip a key cycle (Key-On, start-to-run, Key-Off)
  where driving conditions enable a monitor to run

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Continuous Monitors

• Comprehensive Component Monitor (CCM) tests
  inputs and outputs
• Functionality tests for opens, shorts and
  grounds
• Rationality tests for inaccurate signals
• Some components are tested when key is turned on
• Some components are tested when engine meets
  necessary operating conditions

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Throttle Position Sensor
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Continuous Monitors

• Misfire Monitor
• Constantly monitors engine for misfire
• Determines classification of misfire
• Misfire type A within 200 rpms
• Catalyst damaging
• Logs DTC and flashes MIL
• Misfire type B within 1000 rpms
• Increases emissions
• Logs DTC and illuminates MIL

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Continuous Monitors

• Fuel Monitor
• Monitors long and short term fuel correction
• LTFT
• STFT
• Illuminates MIL and stores DTC when corrections
  exceed preprogrammed limits for extended periods

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Noncontinuous Monitors

• Oxygen Sensor Monitor checks O2S voltage ranges
  and response times
• Catalyst Monitor usually uses downstream O2S to
  check catalyst efficiency
• Looks for low activity on downstream O2S compared
  to upstream O2Ss
• EGR Monitor checks for EGR flow

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Noncontinuous Monitors

• EVAP Monitor
• Non-enhanced monitors effects of purge vapor on
  engine fuel control
• Enhanced monitors effects of purge also checks
  system for leaks
• AIR Monitor checks components and operation of
  secondary air injection system
• Thermostat Monitor (2000) monitors time to
  warm-up
• PCV Monitor (2002) monitors integrity of closed
  crankcase ventilation system

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DTCs

• OBD I codes
• Lack of information vague definitions
• Code retrieval process varied by manufacturer
• Code identification set by manufacturer
• No consistency- too many variables
• Made vehicles difficult to diagnose and repair

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DTCs

• OBD II codes
• A codes sets DTC and illuminates MIL on first
  trip failure (misfire)
• B codes sets DTC and illuminates MIL on second
  consecutive trip failure
• C and D codes non-emission related normally
  will not illuminate MIL, but may illuminate a
  warning lamp

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DTCs

• OBD II codes
• Codes are retrieved and erased with scan tool
  only
• Code set parameters are clearly defined
• Standardized alphanumeric DTC identification
• Freeze frame data
• Data stored with DTC about operating conditions
  when DTC is set
• RPM VSS CTS Engine Load MAP or MAF Fuel
  Status LTFT/STFT

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DTCs

• Pending codes
• One-trip failure for a two-trip DTC
• Sets in memory and stores freeze frame data but
  will not illuminate MIL
• Second consecutive failure- matures into DTC and
  illuminates MIL
• DTC and MIL erasure
• Requires 3 consecutive good trips to turn off MIL
• Requires 40 warm-up cycles to erase DTC

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DTCs

• The OBD-II System DTC Priority is listed below.
• Priority 0Non-emission-related codes
• Priority 1One-trip failure of two-trip fault for
  non-fuel, non-misfire codes
• Priority 2One-trip failure of two-trip fault for
  fuel or misfire codes
• Priority 3Two-trip failure or matured fault of
  non-fuel, non-misfire codes
• Priority 4Two-trip failure or matured fault for
  fuel or misfire codes

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DTC Numbering

• First digit
• P powertrain
• B body system
• C chassis system
• U network communication
• Second digit
• 0 SAE defined (standardized list that applies to
  every vehicle regardless of manufacturer)
• 1 manufacturer specific
• 2 to be used once manufacturer has filled all
  1 code designations

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DTC Numbering

• Third digit
• Assigned to subsystem affected
• 1 air/fuel control
• 2 fuel system (injectors)
• 3 ignition system/ misfire
• 4 auxiliary emission controls (EGR/EVAP/AIR/Cat)
• 5 auxiliary inputs vehicle speed/ idle speed
  control
• 6 computer system (PCM or communications)
• 7 transaxle/transmission
• 8 transaxle/transmission

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DTC Numbering

• Fourth and fifth digits
• Paired numbers
• Indicate exact nature of fault that stored DTC
• Correspond to old OBD I codes
• Example P0300
• Example P0304
• Example P0440

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Generic OBD II

• Displayed data available on all OBD II vehicles
  using a generic scan tool
• Mode 1 powertrain data (PID)
• Mode 2 freeze frame data
• Mode 3 DTCs
• Mode 4 clear DTCs readiness status for
  noncontinuous monitors
• Mode 5 O2S test results
• Mode 6 test results for noncontinuous monitors
• Mode 7 test results for continuous monitors
• Mode 8 bidirectional control of onboard systems
• Mode 9 module identification

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Freeze-frame items include

• Calculated load value
• Engine speed (RPM)
• Short-term and long-term fuel trim percent
• Fuel system pressure (on some vehicles)
• Vehicle speed (MPH)
• Engine coolant temperature
• Intake manifold pressure
• Closed/open-loop status
• Fault code that triggered the freeze-frame
• If a misfire code is set, identify which cylinder
  is misfiring

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Terms to know

• Monitors test performed by diagnostic system
• Enabling criteria exact conditions needed before
  a test can run (provided by a trip)
• Active test test strategy used by PCM that
  changes some aspect of system operation and
  monitors effects of that change
• Passive test test that watches components during
  normal operation but does not take any role in
  testing process
• KOEO Key-On-Engine-Off
• KOER Key-On-Engine-Running
• PID parameter identification- individual items
  in scan tool data display
• Rationality compares sensor inputs to see if
  they make sense
• Readiness Status list of monitors displayed on
  scan tool telling whether various monitors have
  run to completion- does not tell of pass or
  failure only completion
• Warm-up cycle start-to-run where coolant temp
  starts below and rises above 160 degrees F, and
  increases by at least 40 degrees F