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 for rationality and that outputs to powertrain components from the PCM be tested for functionality . Methods for monitoring the various Comprehensive Component monitoring include:

Circuit Continuity
Open
Shorted to Voltage
Shorted to Ground
Rationality and Functionality
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:

Manifold Absolute Pressure (MAP) Sensor
Oxygen Sensor (O2S) (slow response)
Engine Coolant Temperature (ECT) Sensor
Camshaft Position (CMP) Sensor
Vehicle Speed
Crankshaft Position (CKP) Sensor
Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor
Accelerator Pedal Position Sensor (APPS)
Electronic Throttle Control/Throttle Position Sensor (TPS)
Knock Sensors
Oxygen Sensor Heater
PCM
P/N Switch
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:

Fuel Injectors
Air Pump Switchover Solenoid
Manifold Flow Valve Solenoid
Manifold Swirl Valve Solenoid
Ignition Coils
Throttle Body (Electronic Throttle Control/Throttle Position Sensor)
Purge Solenoid
Transmission Controls