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Comprehensive Components

Along with the major monitors, OBD II requires that the vehicle's on-board diagnostic system monitor any component that could affect emissions levels.

OBD II also requires that inputs from powertrain components to the PCM be tested forrationality  and that outputs to powertrain components from the PCM be tested for functionality  . Methods for monitoring the various Comprehensive Component monitoring include:

  1. Circuit Continuity
  2. Open
  3. Shorted to Voltage
  4. Shorted to Ground
  5. Rationality and Functionality
  6. Outputs Tested for functionality
NOTE: Comprehensive component monitors are continuous. Therefore, enabling conditions do not apply. All will set a DTC and illuminate the MIL in 1 trip.

Input Rationality -  While input signals to the PCM are constantly being monitored for electrical opens and shorts, they are also tested for rationality. This means that the input signal is compared against other inputs and information to see if it makes sense under the current conditions.

PCM sensor and CAN Bus inputs that are checked for rationality include:

  1. Manifold Absolute Pressure (MAP) Sensor
  2. Oxygen Sensor (O2S) (slow response)
  3. Engine Coolant Temperature (ECT) Sensor
  4. Camshaft Position (CMP) Sensor
  5. Vehicle Speed
  6. Crankshaft Position (CKP) Sensor
  7. Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor
  8. Accelerator Pedal Position Sensor (APPS)
  9. Electronic Throttle Control/Throttle Position Sensor (TPS)
  10. Knock Sensors
  11. Oxygen Sensor Heater
  12. PCM
  13. P/N Switch
  14. Transmission Control Module

Output Functionality -  PCM outputs are tested for functionality in addition to testing for opens and shorts. When the PCM provides a voltage to an output component, it can verify that the command was carried out by monitoring specific input signals for expected changes. For example, when the PCM commands the Electronic Throttle Control (ETC) Motor to a specific position under certain operating conditions, it expects to see a specific (target) idle speed (RPM). If it does not, it stores a DTC.

PCM outputs monitored for functionality include:

  1. Fuel Injectors
  2. Air Pump Switchover Solenoid
  3. Manifold Flow Valve Solenoid
  4. Manifold Swirl Valve Solenoid
  5. Ignition Coils
  6. Throttle Body (Electronic Throttle Control/Throttle Position Sensor)
  7. Purge Solenoid
  8. Transmission Controls
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