Some of the component monitors are checking for proper operation of the part. Electrically operated components
now have input (rationality) and output (functionality) checks as well as continuity tests (opens/shorts). Previously, a
component like the Throttle Position Sensor (TPS) was checked by the Powertrain Control Module (PCM) for an
open or shorted circuit. If one of these conditions occurred, a Diagnostic Trouble Code (DTC) was set. Now there
is a check to ensure that the component is working. This is done by watching for a TPS indication of a greater or
lesser throttle opening than Manifold Absolute Pressure (MAP) and engine rpm indicate. In the case of the TPS, if
engine vacuum is high and engine rpm is 1600 or greater and the TPS indicates a large throttle opening, a DTC will
be set. The same applies to low vacuum and 1600 rpm.

Any component that has an associated limp-in will set a fault after 1 trip with the malfunction present.

Refer to the appropriate Powertrain Diagnostic Procedure Manual for diagnostic procedures.

The following is a list of the monitored components:

•

Catalyst Monitor

•

Comprehensive Components

•

Exhaust Gas Recirculation (EGR)

•

Fuel Control (rich/lean)

•

Oxygen Sensor Monitor

•

Oxygen Sensor Heater Monitor

•

Purge

•

Misfire

•

Evaporative Vacuum Leak Detection (EVLD)

COMPREHENSIVE COMPONENTS

Along with the major monitors, OBD II requires that the diagnostic system monitor any component that could affect
emissions levels. In many cases, these components were being tested under OBD I. The OBD I requirements
focused mainly on testing emissions-related components for electrical opens and shorts.

However, 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 vari-
ous 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 from the Controller Antilock Brake (CAB)

•

Crankshaft Position (CKP) Sensor

•

Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor

•

Accelerator Pedal Position Sensor (APPS)

•

Throttle Position Sensor (TPS)

•

Knock Sensors

•

Oxygen Sensor Heater

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EMISSIONS CONTROL

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