OBD II System Monitors: Overview

The OBD II system meets government regulations by monitoring the emission control system. When a system or component exceeds emission thresholds or a component operates outside of tolerance, a DTC will be stored and the MIL will be illuminated.

Fault detection strategy and MIL operation are associated with trips and drive cycles. Each monitor has requirements for setting and clearing DTCs and for controlling the MIL. These processes, DTC and MIL operation, descriptions of the monitors and the definition of Trip and drive cycles are discussed in detail within this section.

The "Diagnostic Executive" is the computer program in the Electronic Engine Control-V (EEC-V) Powertrain Control Module (PCM) that coordinates the OBD II self-monitoring system. This program controls all the monitors and interactions, DTC and MIL operation, freeze frame data and scan tool interface.

"Freeze Frame Data" describes stored engine conditions such as state of the engine, state of fuel control, spark, RPM, load, and warm-up status at the point the first malfunction is detected. Previously stored conditions will be replaced only if a fuel or misfire malfunction is detected. This data is accessible by the scan tool to assist in repairing the vehicle.

OBD II Inspection Maintenance (IM) Readiness Code P1000 is the DTC that identifies the monitors that have not completed since the computer memory was last cleared. In certain states, it may be necessary to operate the vehicle until this code is erased from the PCM in order to purchase a vehicle license.

The OBD II Monitors are:

- Catalyst Efficiency Monitor Catalyst Efficiency Monitor

- Comprehensive Component Monitor Comprehensive Component Monitor

- Exhaust Gas Recirculation (EGR) Monitor Exhaust Gas Recirculation System Monitor

- Fuel System Monitor Fuel System Monitor

- HO2S Monitor Heated Oxygen Sensor Monitor

- Misfire Detection Monitor Misfire Detection Monitor