General System Description

ON BOARD DIAGNOSTICS II

The On Board Diagnostic II (OBD II) system meets government regulations by monitoring the emission control system. When a component or system operates outside of allowable standards, a Diagnostic Trouble Code (DTC) is stored and the Malfunction Indicator Lamp (MIL) will be illuminated.

Two additional Heated Oxygen Sensors (HO2S) are added to determine the efficiency of the catalytic converters. The sensors are the same type used for fuel control, but have different functions.

OBD II will require vehicles to be equipped with the following common features:

- Diagnostic connector

- Diagnostic input/output data

- Diagnostic procedures

- Terminology

- New emission related sensors

Fault detection strategy and MIL operation are associated with Trips (specific instructions for vehicle operation within a period of time) and Drive cycles.

DIAGNOSTIC EXECUTIVE

The Diagnostic Executive is the computer program in the Electronic Engine Control-V (EEC-V) Powertrain Control Module (PCM) coordinating the OBD II self monitoring system. This program controls all the monitors, interactions, Diagnostic Trouble Code (DTC) and Malfunction Indicator Lamp (MIL) operation, Freeze Frame Data and scan tool interface. Each monitor has requirements for setting and clearing DTC's and for controlling the MIL.

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

FREEZE FRAME DATA

Freeze Frame Data describes stored engine conditions such as, state of the engine, fuel control, spark, rpm, load and warm-up status when 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 a scan tool.

INSPECTION MAINTENANCE (IM) READINESS CODE

OBD II IM Readiness Code P1000 is the DTC that identifies the monitors that have not completed since the computer memory was last cleared.