Inspection and Maintenance - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 190

Table 13.3 Main functions of OBD in self ignition engines
Combustion system Exhaust gas after treatment

Irregular operation of engine (misfire)
Fuel amount
Charge pressure
CAN bus communication

Exhaust Gas Recirculation (EGR)
Particle filter
Control devices
k sensor

Misfires causing an engine to run roughly are the most serious indication of
ignition problems. There are two different classes of misfires

• Irregular operations that endanger the engine; and
• Exhaust gas misfires that endanger the catalyst.

OBD technology permanently records the rough running of the engine from the
angle speed of the crankshaft. If the rough running exceeds the limit, the number
of misfires is counted [ 9 ].
The monitored systems are checked at specified intervals once per driving
cycle, if the main operating conditions are within the defined range. The conditions
are the operation temperature of the catalyst, the temperature of the coolant, the
number of revolutions, the engine load and the status of the secondary air system.
If the conditions are not in the defined range, the diagnostic function is not
processed [ 10 ].
Besides thermal or mechanical deterioration of the catalyst, the normal aging
process lowers its normal conversion rate. The exhaust gas after treatment system
contains the mixture controlling and monitoring k sensors. The catalyst's oxygen
storage capability is measured to determine its operability. The storage capacity is
represented by the comparison of the mixture controlling k signal (upstream of the
catalyst) with the monitoring k signal (downstream of the catalyst) [ 11 ].
The tank ventilation system is controlled by the electric function of the tank
ventilation valve. In Europe, tank leak diagnosis is not required in contrast to the
OBD II in the USA. The manufacturer must merely ensure the tightness of the
filler cap. This can be done with the help of an electronic control system or a
security tape [ 12 ].

13.1.2 OBD in Vehicles with Self Ignition Engine

The monitoring of self ignition engines originates from the technology in spark
ignition engines. In Europe, the legal system of rules (98/69/EC) comprehensively
prescribes the requirements of the OBD technology in vehicles with a self ignition
engine (see Table 13.3 )[ 13 ].
The OBD in a self ignition engine with Common Rail technology is shown in
the Fig. 13.4 [ 14 ].