Cartridge Solenoid Valve Status
Check which APS2 variant is installed on the truck. If it is a 'high capacity' variant correct parametrization, otherwise replace ECU due to erroneous detection of external load.
What you'll see
No driver-visible symptom recorded.
System reaction
The behavior of the APS2 is as expected from an 'advanced' variant, i.e. the cartridges are not switched. Compressed air is delivered into the system only through the first cartridge, while dried air for regeneration purposes is released only through the second cartridge. As a consequence of this the entire system gets wet.
Diagnostic depth
A special open load check is executed after startup if the device is configured as an 'advanced' variant to detect whether a solenoid valve is connected to the cartridge valve output stage.
A load, probably a solenoid valve, has been detected at the output stage of the cartridge solenoid valve although the device is configured as an 'advanced' variant.