Diagnostic Trouble Code Retrieval

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Diagnostic Trouble Code Retrieval
Advanced Engine Performance Diagnosis 3rd Edition
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Diagnostic Trouble Code Retrieval

• Methods For Clearing Diagnostic Trouble Codes
• Clearing Codes Method 1
• The preferred method to clear codes is by using a
  scan tool.
• Clearing Codes Method 2
• If a scan tool is not available or a scan tool
  cannot be used on the vehicle being serviced, the
  power to the computer can be disconnected.
• Disconnect a fusible link, if so equipped, which
  feeds the computer.
• Disconnect the fuse or fuses that feed the
  computer.

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• Methods For Clearing Diagnostic Trouble Codes
  (continued)
• Clearing Codes Method 3
• If the other two methods cannot be performed, the
  negative (-) battery cable can be disconnected to
  clear stored DTCs.

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• Flash Code Retrieval On OBD General Motors
  Vehicles
• Turn the ignition switch on (engine off). The
  check engine light or service engine soon
  light should be on. If the amber malfunction
  indicator light (MIL) is not on, the problem
  exists within the light circuit.
• Connect terminals A and B at the DLC.

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• Flash Code Retrieval On OBD General Motors
  Vehicles (contd)
• Observe the MIL. A code 12 (one flash, then a
  pause, then two flashes) reveals that there is no
  engine speed indication to the computer and
  because the engine is not running, this simply
  indicates that the computer diagnostic system is
  working correctly.
• After code 12 is displayed three times, the MIL
  will flash any other stored DTCs in numeric order
  starting with the lowest-number code. If only
  code 12 is displayed another three times, the
  computer has not detected any other faults.

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• Retrieving Ford Diagnostic Codes (continued)
• Continuous memory codes
• Continuous memory codes are set based on
  information stored while the vehicle was in
  normal operation.
• These codes represent an intermittent problem and
  should only be used for diagnosis if the KOEO
  test results in code 11 (no faults detected).
• Therefore, any codes displayed after the
  separation pulse represent failures that have
  been detected but may no longer be present.

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• Retrieving Ford Diagnostic Codes (continued)
• Steering, brake and overdrive switch test
• To test the power steering pressure switch, the
  technician must turn the steering wheel one-half
  turn after the ID code has been displayed.
• The brake pedal and the overdrive cancel switch
  must also be cycled after the ID code to allow
  the system to detect a change of state of these
  switches.

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• Retrieving Ford Diagnostic Codes (continued)
• Dynamic response check
• The dynamic response test checks the throttle
  position (TP) mass airflow (MAF) and manifold
  absolute pressure (MAP) sensors during a brief
  wide-open throttle (WOT) test performed by the
  technician.
• The signal for the technician to depress the
  throttle briefly to wide open is a single pulse
  or a code 10 on a STAR tester.

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• Retrieving OBD II Codes 16 Pin
• A scan tool is required to retrieve DTCs from an
  OBD II vehicle.
• Every OBD II scan tool will be able to read all
  generic Society of Automotive Engineers (SAE)
  DTCs from any vehicle.

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• DTC Numbering Explanation
• The number in the hundredth position indicates
  the specific vehicle system or subgroup that
  failed.
• This position should be consistent for P0xxx and
  P1xxx type codes.

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• DTC Numbering Explanation (continued)
• The following numbers and systems were
  established by SAE
• P0100 Air metering and fuel system fault
• P0200 Fuel system (fuel injector only) fault
• P0300 Ignition system or misfire fault
• P0400 Emission control system fault
• P0500 Idle speed control, vehicle speed sensor
  fault
• P0600 Computer output circuit (relay, solenoid,
  etc.) fault
• P0700 Transaxle, transmission faults

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• OBD II Active Tests
• OBD II is an active computer analysis system
  because it actually tests the operation of the
  oxygen sensor, exhaust gas recirculation system,
  and other systems whenever conditions permit.

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• Types of DTCs
• Type A codes
• A type A DTC is emission-related and will cause
  the MIL to be turned on on the first trip if the
  computer has detected a problem.
• Engine misfire or a very rich or lean air-fuel
  ratio, for example, would cause a type A DTC.
• These codes alert the driver to an emission
  problem that may cause damage to the catalytic
  converter.

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• Types of DTCs (continued)
• Type B codes
• A type B code will be stored and the MIL will be
  turned on during the second consecutive trip,
  alerting the driver to the fact that a diagnostic
  test was performed and failed.
• Type C and D codes
• Type C and D codes are for use with
  non-emission-related diagnostic tests they will
  cause the lighting of a service lamp (if the
  vehicle is so equipped).
• Type C does are also called type C1 codes and D
  codes are also called type C0 codes.

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• Clearing OBD II DTCs
• A DTC should not be cleared from the vehicle
  computer memory unless the fault has been
  corrected and the technician is so directed by
  the diagnostic procedure.
• If the problem that caused the DTC to be set has
  been corrected, the computer will automatically
  clear the DTC after 40 consecutive warm-up cycles
  with no further faults detected (misfire and
  excessively rich or lean condition codes required
  80 warm-up cycles).

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• Clearing OBD II DTCs (continued)
• The codes can also be erased by using a scan
  tool.
• NOTE Disconnecting the battery may not erase
  OBD II DTCs or freeze-frame data. Most vehicle
  manufacturers recommend using a scan tool to
  erase DTCs rather than disconnecting the battery
  because the memory for the radio, seats, and
  learned engine operating parameters are lost if
  the battery is disconnected.

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• CHAPTER SUMMARY
• Care should be taken to not induce high voltage
  or current around any computer or
  computer-controlled circuit or sensor.
• A thorough visual inspection is the first step in
  the diagnosis and troubleshooting of any engine
  performance problem or electrical malfunction.
• If the MIL is on, retrieve the DTC and follow the
  manufacturers recommended procedure to find the
  root cause of the problem.
• All DTCs should be cleared after the repair.
• OBD II vehicles use a 16-pin DLC and common DTCs.

Advanced Engine Performance Diagnosis