Vehicles that are parked in enclosed premises until such time as they are required for use are often connected to exhaust extraction systems throughout their immobilization period. These exhaust extraction systems are then activated immediately before an engine start. An example worthy of mentioning here is that of fire department emergency vehicles. By doing so one ensures that the emissions frequently generated during a starting procedure do not escape into the surrounding area - in this case the fire department's engine house.
Permanently connected exhaust extraction systems however, can lead to errors occurring in the exhaust gas aftertreatment (ACM) control unit. To avoid this, the system-related vacuum generated in the exhaust extraction system must never be more than 2 mbar.
Basically, these faults are always ones that occur in relation to the values determined by the two pressure sensors connected to the exhaust gas aftertreatment unit. Such as the following, e.g.:
Too high, too low or implausible exhaust gas back pressures
Too high, too low or implausible pressure differentials
Leaks can occur on the exhaust system
Clogged, broken or missing diesel particulate filter
Or faults in which one of the two pressure sensors appears to be the cause itself, such as, e.g. :
The signal of component 'B37 (exhaust pressure sensor upstream of diesel oxidation catalytic converter)' is implausible.
The signal of component 'B38 (exhaust pressure sensor downstream of diesel particulate filter)' is implausible.