Main faults of the engine management system (VW Passat B5)

Before troubleshooting, make sure that there is sufficient fuel in the fuel tank, the engine has no mechanical defects, the battery is charged and the starter turns the engine crankshaft at a sufficient speed, the engine preheating system is in good condition, the fuel system is sealed and free of contamination, the crankcase ventilation hose is clean and the powertrain ground bus is securely connected.

Pre-check the faults recorded in the engine management system memory.

Cause	Method of elimination
Difficulty starting the engine or the engine does not start at all
The diesel engine preheating system does not work	Check and, if necessary, restore the functionality of the diesel engine preheating system.
The fuel shut-off valve does not open	Check the fuel shut-off valve of the engine control unit and the anti-theft system.
Defect in the fuel supply system	Check the fuel supply system to the engine.
Fuel supply lines are leaky, blocked internally or deformed	Clean and, if necessary, replace the fuel supply lines.
The fuel filter is dirty	Replace the fuel filter.
In winter, there is water or ice in the fuel filter	Warm up the car in a heated garage.
The fuel tank ventilation is clogged or the fuel filter located in the fuel tank is dirty	Clean the fuel tank ventilation system or fuel filter.
Fuel injection timing is incorrectly adjusted	Check and adjust fuel injection timing if necessary.
The fuel injectors are faulty	Check the functionality of the fuel injectors.
The high pressure fuel pump is faulty	Replace the high pressure fuel pump.
The engine only runs at idle speed
The fuel hoses on the high pressure fuel pump or on the fuel filter are loose	Secure the fuel hoses properly.
The fuel supply and return hoses on the high pressure fuel pump are not connected correctly	Check that the fuel hoses are connected correctly.
Increased fuel consumption
The fuel filter is dirty	Replace the fuel filter.
The fuel system is leaking	Check the fuel system for leaks.
The fuel return line is dirty	Clean the fuel return line.