Fuel System & Fault Isolation - 1.8L: Overview Kia Spectra II

Scheme 2

Scheme 3

Scheme 4

OBD-II OVERVIEW

The goal of the On Board Diagnostics-II (OBD-II) regulation, which was mandated by the Environmental Protection Agency (EPA), is to ensure proper emission system operation for the life of the vehicle by providing the vehicle with an "on-board" diagnostic system which is capable of continuously monitoring the efficiency of the emission control system.

To achieve this goal, OBD-II diagnostics monitors emissions-related components and systems for deterioration and identifies an emissions-related malfunction before the driver notices a problem with the vehicle.

The ECM illuminates the Malfunction Indicator Light (MIL) and stores a Diagnostic Trouble Code (DTC) for some failures in the Emissions System. The DTCs are retrieved using SST connected to the standardized OBD-II Data Link Connector (DLC) located below the left side of the instrument panel.

OBD-II diagnostics supports not only the standard test mode of OBD-II (Mode 01 -Mode 07) but also an advanced test Mode (Mode 22: Supported PID - analog inputs and outputs, digital inputs and outputs). All of these diagnostic test modes are supported using SST through the DLC.

The ECM executes the following key monitoring for OBD-II

1. Primary emission control system/components
2. Heated oxygen sensors (includes heater)
3. Catalyst
4. Fuel system
5. Evaporative emission system
6. Misfire
7. Comprehensive components (input and output)

SYSTEM DESCRIPTION

The front Oxygen Sensor is mounted in the exhaust system in front of the warm-up Catalytic Converter so it can monitor the oxygen content of the exhaust gases leaving the Engine. By constantly monitoring the voltage output of the Heated Oxygen Sensor, the ECM calculates the fuel mixture correction to the injector pulse width. To activate the sensor faster and lower emissions, a heated Oxygen Sensor is incorporated.

Additionally, the rear heated Oxygen Sensor is installed downstream of the warm-up catalytic converter for catalyst monitoring.

THREE WAY CATALYTIC CONVERTER (TWC) MONITORING SYSTEM DESCRIPTION

The ECM has the capability of monitoring three way catalytic converter efficiently by using a second Heated Oxygen Sensor (Rear HO2S) located in the exhaust, downstream of the TWC converter. This sensor will also produce an output signal indicating the oxygen storage capacity of the TWC converter which will indicate how effectively the TWC can convert exhaust emissions into harmless gases.

TWC monitoring is based on monitoring the oxygen storage capability. The correction between conversion efficiency and storage capability has been shown in various investigations. The engine control results in regular lambda oscillations of the exhaust gas (lambda = normalized air fuel ratio). These oscillations are dampened by the storage activity of the three way catalytic converter.

The amplitude of the remaining lambda oscillations downstream of the TWC converter indicates its storage capability. The method uses the amplitude ratio of the signal oscillations of upstream and downstream lambda sensors as raw information. This information is evaluated separately in different engine load and speed ranges. If there is an indication of low storage capability in a certain number of operating ranges, a defective TWC converter is recognized. According to the described operating principle, the following main parts can be distinguished

Scheme 5

1. Computation of the amplitude ratio as raw information
2. Post-processing in different engine load and speed rages
3. Fault evaluation
4. Check of monitoring conditions

The determination of how much fuel to deliver to the engine is the calculation of injector pulse width. Basic injection duration (injector pulse width) is determined by

1. Engine load (MAF sensor)
2. Engine Speed (SGT)
3. Short fuel trim correction factor
4. Long fuel trim correction factor
5. Fuel trim is monitored to meet the OBD-II requirements

1. Short fuel trim (FT) Short FT is a temporary correction to fuel delivery which changes with every cycle of the front Heated Oxygen Sensor. Under normal conditions, it fluctuates rapidly around its ideal value of 0% correction and is set to 0% during open loop operation. Short FT is a parameter of the OBD-II serial data stream and can be displayed by a scan tool. The normal range of short FT is +/-25%, but under normal operating conditions it rarely goes beyond +/-10%. Short FT responds to changes in front HO2S output. If basic injection duration results in a lean air/fuel ratio, Short FT responds with positive corrections (+1% to +25%) to add fuel and enrich the mixture. If basic injection is too rich, Short FT responds with negative corrections (-1% to -25%) to subtract fuel and lean the mixture.
2. Long fuel trim Long FT is a data parameter on the OBD-II data streams. It is a more permanent correction to fuel delivery because it is part of the basic injection duration calculation. Long FT changes slowly, in response to Short FT. It's normal range is +/-25%, positive values indicating rich correction and negative values indicating lean correction. Unlike Short FT which affects injection duration calculation in closed loop only, the Long FT correction factor affects the basic injection duration calculation in open and closed loop. Because Long FT is stored in a non-volatile RAM and is not erased when the ignition is switched OFF, the fuel system is able to correct for variances in engine and fuel conditions even during warm-up and wide open throttle conditions. MONITORING PROCESS The ECM monitors the averages of long term and short term fuel trim. If these fuel trim values reach and stay at their maximum limits (+/-25%) for a defined period of time, a diagnostic trouble code is set.