The Comprehensive Component Monitor (CCM) monitors for malfunctions in any powertrain electronic component or circuit that provides input or output signals to the Powertrain Control Module (PCM) that can affect emissions and is not monitored by another OBD II monitor. Inputs and outputs are, at a minimum, monitored for circuit continuity or proper range of values. Where feasible, inputs are also checked for rationality, outputs are also checked for proper functionality.
CCM covers many components and circuits and tests them in various ways depending on the hardware, function, and type of signal. For example, analog inputs such as Throttle Position or Engine Coolant Temperature are typically checked for opens, shorts and out-of-range values. This type of monitoring is performed continuously. Some digital inputs like Vehicle Speed or Crankshaft Position rely on rationality checks - checking to see if the input value makes sense at the current engine operating conditions. These types of tests may require monitoring several components and can only be performed under appropriate test conditions.
Outputs such as the Idle Air Control solenoid are checked for opens and shorts by monitoring a feedback circuit or "smart driver" associated with the output. Other outputs, such as relays, require additional feedback circuits to monitor the secondary side of the relay. Some outputs are also monitored for proper function by observing the reaction of the control system to a given change in the output command. An Idle Air Control solenoid can be functionally tested by monitoring idle rpm relative to the target idle rpm. Some tests can only be performed under appropriate test conditions; for example, transmission shift solenoids can only be tested when the PCM commands a shift.
The following is an example of some of the input and output components monitored by the CCM. The components monitor may belong to the engine, ignition, transmissions, air conditioning, or any other PCM supported subsystem.
Inputs: Mass Air Flow (MAF) sensor, Intake Air Temperature (IAT) sensor, Engine Coolant Temperature (ECT) sensor, Throttle Position (TP) sensor, Camshaft Position (CMP) sensor, Air Conditioning Pressure Sensor (ACPS) , Fuel Tank Pressure (FTP) sensor.
Outputs: Fuel Pump(FP) , Wide Open Throttle A/C Cutout (WAC) , Idle Air Control (IAC) , Shift Solenoid(SS) , Torque Converter Clutch (TCC) solenoid, Intake Manifold Runner Control (IMRC) , Evaporative Emission (EVAP) canister purge valve, Canister Vent (CV) solenoid.
CCM is enabled after the engine starts and is running. A Diagnostic Trouble Code (DTC) is stored in Keep Alive Memory and the Malfunction Indicator Lamp(MIL) is illuminated after two driving cycles when a malfunction is detected. Many of the CCM tests are also performed during on demand self-test.