OBD II Readiness Monitors

Continuous Monitors

Comprehensive Component Monitor

The PCM executes the comprehensive component monitor whenever the engine is in operation. The monitor tests for concerns in any powertrain electronic component or circuit that provides input or output signals to the PCM that can affect emissions and is not monitored by another on board diagnostics (OBD) monitor. Inputs and outputs are, at a minimum, monitored for circuit continuity or correct range of values. Where feasible, inputs are also checked for rationality, and outputs are also checked for correct functionality.

Comprehensive component monitoring covers many components and circuits and tests them in various ways depending on 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. Some digital inputs like brake switch or crankshaft position rely on rationality checks - checking to see if the input value makes sense at the current engine operating conditions.

Outputs such as coil drivers are checked for opens and shorts by monitoring a feedback circuit or smart driver associated with the output. Some outputs are also monitored for correct 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 the idle RPM relative to the target idle RPM. Some tests can only be carried out under the appropriate test conditions. For example, the transmission shift solenoids can only be tested when the PCM commands a shift.