On–board Diagnosis (OBD)
The main reason for introducing the OBD is the "Guideline 98/69/EU on reducing vehicle emissions" dated 28/12/1998.
A further reason for the introduction of OBD is that malfunctions may occur that sometimes may not be determined in time due to the ever increasing maintenance intervals and the periods between exhaust gas tests.
To fulfil the future legal requirements with reference to environmental protection, increased requirements are made of individual components.
With the introduction of control units that are capable of making diagnoses, the step towards OBD was completed.
The OBD regulations govern the manner of electronic functions for monitoring the exhaust gas characteristics of modern vehicle engines. The aim of this electronic monitoring is the permanent guarantee of a minimised exhaust gas characteristic for vehicles in operation.
The principle of OBD is to detect errors relating to the exhaust gas, to save them and to display them via a telltale MIL (Malfunction Indicator Light or also exhaust gas telltale) in the instrument panel. These faults relating to the exhaust gas are read out via a diagnostics device. This enables the components in the vehicle relating to the exhaust gas to be monitored continuously.
The following exhaust gas–relevant components are monitored:
- Catalytic converter (or catalytic converters)
- Crankshaft sensor
- Camshaft sensor
- Throttle valve module
- Ignition module
- Mass air flow meter
- Intake air temperature sensor
- Coolant temperature sensor.
- Permanent memory
- Injectors
4.80 On–board Diagnosis (OBD)
If error functions occur in the engine management, these may negatively affect emissions, without the driver noticing this malfunction. Misfires could be a cause of this kind which may lead to the destruction of the catalytic converter (catalytic converters).
Far more information can be read out from the error memory than with the previously used methods due to these additional monitoring functions and the additional information of the OBD.
In the OBD, not only the purely electrical components are monitored, but also all exhaust–gas relevant systems and processes.
The following systems, components and processes are monitored:
- Oxygen sensors
- Misfires
- Exhaust gas recirculation system
- Tank vent system
- Fuel system
- Emission–relevant components and assemblies
- Control units
If deviations from the specified tolerances are determined, a corresponding error code is stored in the permanent memory. If an exhaust gas–relevant error repeats, the exhaust gas telltale is illuminated.